diff --git a/samples/ControlCatalog/App.xaml b/samples/ControlCatalog/App.xaml
index 227b31bf20..d0e1bd885e 100644
--- a/samples/ControlCatalog/App.xaml
+++ b/samples/ControlCatalog/App.xaml
@@ -3,6 +3,7 @@
              xmlns:vm="using:ControlCatalog.ViewModels"
              x:DataType="vm:ApplicationViewModel"
              x:CompileBindings="True"
+             Name="Avalonia ControlCatalog"
              x:Class="ControlCatalog.App">
   <Application.Styles>
     <Style Selector="TextBlock.h1, TextBlock.h2, TextBlock.h3">
diff --git a/samples/ControlCatalog/Models/Person.cs b/samples/ControlCatalog/Models/Person.cs
index 47f41bc584..cd70fa3959 100644
--- a/samples/ControlCatalog/Models/Person.cs
+++ b/samples/ControlCatalog/Models/Person.cs
@@ -16,6 +16,7 @@ namespace ControlCatalog.Models
         string _firstName;
         string _lastName;
         bool _isBanned;
+        private int _age;
 
         public string FirstName
         {
@@ -59,6 +60,20 @@ namespace ControlCatalog.Models
             }
         }
 
+        
+        /// <summary>
+        ///    Gets or sets the age of the person
+        /// </summary>
+        public int Age
+        {
+            get => _age;
+            set
+            {
+                _age = value;
+                OnPropertyChanged(nameof(Age));
+            }
+        }
+
         Dictionary<string, List<string>> _errorLookup = new Dictionary<string, List<string>>();
 
         void SetError(string propertyName, string error)
diff --git a/samples/ControlCatalog/Pages/CalendarDatePickerPage.xaml b/samples/ControlCatalog/Pages/CalendarDatePickerPage.xaml
index 3e50bf8a08..2fe16ba8e3 100644
--- a/samples/ControlCatalog/Pages/CalendarDatePickerPage.xaml
+++ b/samples/ControlCatalog/Pages/CalendarDatePickerPage.xaml
@@ -1,5 +1,7 @@
 <UserControl xmlns="https://github.com/avaloniaui"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:vm="clr-namespace:ControlCatalog.ViewModels"
+             x:DataType="vm:MainWindowViewModel"
              x:Class="ControlCatalog.Pages.CalendarDatePickerPage">
   <StackPanel Orientation="Vertical" Spacing="4">
     <TextBlock Classes="h2">A control for selecting dates with a calendar drop-down</TextBlock>
@@ -39,6 +41,9 @@
                 
         <TextBlock Text="Disabled"/>
         <CalendarDatePicker IsEnabled="False"/>
+        
+        <TextBlock Text="Validation Example"/>
+        <CalendarDatePicker SelectedDate="{CompiledBinding ValidatedDateExample, Mode=TwoWay}"/>
       </StackPanel>
 
     </StackPanel> 
diff --git a/samples/ControlCatalog/Pages/DataGridPage.xaml b/samples/ControlCatalog/Pages/DataGridPage.xaml
index 63e873d9b5..f7e3cf2441 100644
--- a/samples/ControlCatalog/Pages/DataGridPage.xaml
+++ b/samples/ControlCatalog/Pages/DataGridPage.xaml
@@ -64,6 +64,18 @@
               <DataGridTextColumn Header="First Name" Binding="{Binding FirstName}" Width="2*" FontSize="{Binding #FontSizeSlider.Value, Mode=OneWay}" />
               <DataGridTextColumn Header="Last" Binding="{Binding LastName}" Width="2*" FontSize="{Binding #FontSizeSlider.Value, Mode=OneWay}" />
               <DataGridCheckBoxColumn Header="Is Banned" Binding="{Binding IsBanned}" Width="*" IsThreeState="{Binding #IsThreeStateCheckBox.IsChecked, Mode=OneWay}" />
+              <DataGridTemplateColumn Header="Age" >
+                <DataGridTemplateColumn.CellTemplate>
+                  <DataTemplate DataType="local:Person">
+                    <TextBlock Text="{Binding Age, StringFormat='{}{0} years'}" VerticalAlignment="Center" HorizontalAlignment="Center" />
+                  </DataTemplate>
+                </DataGridTemplateColumn.CellTemplate>
+                <DataGridTemplateColumn.CellEditingTemplate>
+                  <DataTemplate DataType="local:Person">
+                    <NumericUpDown Value="{Binding Age}" FormatString="N0" HorizontalAlignment="Stretch" Minimum="0" Maximum="120" TemplateApplied="NumericUpDown_OnTemplateApplied" />
+                  </DataTemplate>
+                </DataGridTemplateColumn.CellEditingTemplate>
+              </DataGridTemplateColumn>
             </DataGrid.Columns>
           </DataGrid>
           <Button Grid.Row="1" Name="btnAdd" Margin="12,0,12,12" Content="Add" HorizontalAlignment="Right" />
diff --git a/samples/ControlCatalog/Pages/DataGridPage.xaml.cs b/samples/ControlCatalog/Pages/DataGridPage.xaml.cs
index dc5cc49a90..c010d38eac 100644
--- a/samples/ControlCatalog/Pages/DataGridPage.xaml.cs
+++ b/samples/ControlCatalog/Pages/DataGridPage.xaml.cs
@@ -6,7 +6,9 @@ using Avalonia.Controls;
 using Avalonia.Markup.Xaml;
 using ControlCatalog.Models;
 using Avalonia.Collections;
+using Avalonia.Controls.Primitives;
 using Avalonia.Data;
+using Avalonia.Threading;
 
 namespace ControlCatalog.Pages
 {
@@ -48,9 +50,9 @@ namespace ControlCatalog.Pages
 
             var items = new List<Person>
             {
-                new Person { FirstName = "John", LastName = "Doe" },
-                new Person { FirstName = "Elizabeth", LastName = "Thomas", IsBanned = true },
-                new Person { FirstName = "Zack", LastName = "Ward" }
+                new Person { FirstName = "John", LastName = "Doe" , Age = 30},
+                new Person { FirstName = "Elizabeth", LastName = "Thomas", IsBanned = true , Age = 40 },
+                new Person { FirstName = "Zack", LastName = "Ward" , Age = 50 }
             };
             var collectionView3 = new DataGridCollectionView(items);
 
@@ -84,5 +86,19 @@ namespace ControlCatalog.Pages
                 return Comparer.Default.Compare(x, y);
             }
         }
+
+        private void NumericUpDown_OnTemplateApplied(object sender, TemplateAppliedEventArgs e)
+        {
+            // We want to focus the TextBox of the NumericUpDown. To do so we search for this control when the template
+            // is applied, but we postpone the action until the control is actually loaded. 
+            if (e.NameScope.Find<TextBox>("PART_TextBox") is {} textBox)
+            {
+                Dispatcher.UIThread.InvokeAsync(() =>
+                {
+                    textBox.Focus();
+                    textBox.SelectAll();
+                }, DispatcherPriority.Loaded);
+            }
+        }
     }
 }
diff --git a/samples/ControlCatalog/ViewModels/MainWindowViewModel.cs b/samples/ControlCatalog/ViewModels/MainWindowViewModel.cs
index 4b3cfa9c9d..2b0c30f311 100644
--- a/samples/ControlCatalog/ViewModels/MainWindowViewModel.cs
+++ b/samples/ControlCatalog/ViewModels/MainWindowViewModel.cs
@@ -5,6 +5,7 @@ using Avalonia.Controls.Notifications;
 using Avalonia.Dialogs;
 using Avalonia.Platform;
 using System;
+using System.ComponentModel.DataAnnotations;
 using MiniMvvm;
 
 namespace ControlCatalog.ViewModels
@@ -164,5 +165,17 @@ namespace ControlCatalog.ViewModels
         public MiniCommand ExitCommand { get; }
 
         public MiniCommand ToggleMenuItemCheckedCommand { get; }
+
+        private DateTime? _validatedDateExample;
+
+        /// <summary>
+        ///    A required DateTime which should demonstrate validation for the DateTimePicker
+        /// </summary>
+        [Required]
+        public DateTime? ValidatedDateExample
+        {
+            get => _validatedDateExample;
+            set => this.RaiseAndSetIfChanged(ref _validatedDateExample, value);
+        }
     }
 }
diff --git a/src/Avalonia.Animation/Animatable.cs b/src/Avalonia.Animation/Animatable.cs
index 4811028f85..50fc5ac73b 100644
--- a/src/Avalonia.Animation/Animatable.cs
+++ b/src/Avalonia.Animation/Animatable.cs
@@ -157,7 +157,7 @@ namespace Avalonia.Animation
                             state.Instance?.Dispose();
                             state.Instance = transition.Apply(
                                 this,
-                                Clock ?? AvaloniaLocator.Current.GetService<IGlobalClock>(),
+                                Clock ?? AvaloniaLocator.Current.GetRequiredService<IGlobalClock>(),
                                 oldValue,
                                 newValue);
                             return;
@@ -169,7 +169,7 @@ namespace Avalonia.Animation
             base.OnPropertyChangedCore(change);
         }
 
-        private void TransitionsCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
+        private void TransitionsCollectionChanged(object? sender, NotifyCollectionChangedEventArgs e)
         {
             if (!_transitionsEnabled)
             {
@@ -179,14 +179,14 @@ namespace Avalonia.Animation
             switch (e.Action)
             {
                 case NotifyCollectionChangedAction.Add:
-                    AddTransitions(e.NewItems);
+                    AddTransitions(e.NewItems!);
                     break;
                 case NotifyCollectionChangedAction.Remove:
-                    RemoveTransitions(e.OldItems);
+                    RemoveTransitions(e.OldItems!);
                     break;
                 case NotifyCollectionChangedAction.Replace:
-                    RemoveTransitions(e.OldItems);
-                    AddTransitions(e.NewItems);
+                    RemoveTransitions(e.OldItems!);
+                    AddTransitions(e.NewItems!);
                     break;
                 case NotifyCollectionChangedAction.Reset:
                     throw new NotSupportedException("Transitions collection cannot be reset.");
@@ -204,7 +204,7 @@ namespace Avalonia.Animation
 
             for (var i = 0; i < items.Count; ++i)
             {
-                var t = (ITransition)items[i];
+                var t = (ITransition)items[i]!;
 
                 _transitionState.Add(t, new TransitionState
                 {
@@ -222,7 +222,7 @@ namespace Avalonia.Animation
 
             for (var i = 0; i < items.Count; ++i)
             {
-                var t = (ITransition)items[i];
+                var t = (ITransition)items[i]!;
 
                 if (_transitionState.TryGetValue(t, out var state))
                 {
diff --git a/src/Avalonia.Animation/Animation.cs b/src/Avalonia.Animation/Animation.cs
index a4515db514..03b2d17e44 100644
--- a/src/Avalonia.Animation/Animation.cs
+++ b/src/Avalonia.Animation/Animation.cs
@@ -203,7 +203,7 @@ namespace Avalonia.Animation
         /// </summary>
         /// <param name="setter">The animation setter.</param>
         /// <returns>The property animator type.</returns>
-        public static Type GetAnimator(IAnimationSetter setter)
+        public static Type? GetAnimator(IAnimationSetter setter)
         {
             if (s_animators.TryGetValue(setter, out var type))
             {
@@ -254,7 +254,7 @@ namespace Avalonia.Animation
             Animators.Insert(0, (condition, typeof(TAnimator)));
         }
 
-        private static Type GetAnimatorType(AvaloniaProperty property)
+        private static Type? GetAnimatorType(AvaloniaProperty property)
         {
             foreach (var (condition, type) in Animators)
             {
@@ -276,6 +276,11 @@ namespace Avalonia.Animation
             {
                 foreach (var setter in keyframe.Setters)
                 {
+                    if (setter.Property is null)
+                    {
+                        throw new InvalidOperationException("No Setter property assigned.");
+                    }
+
                     var handler = Animation.GetAnimator(setter) ?? GetAnimatorType(setter.Property);
 
                     if (handler == null)
@@ -305,7 +310,7 @@ namespace Avalonia.Animation
 
             foreach (var (handlerType, property) in handlerList)
             {
-                var newInstance = (IAnimator)Activator.CreateInstance(handlerType);
+                var newInstance = (IAnimator)Activator.CreateInstance(handlerType)!;
                 newInstance.Property = property;
                 newAnimatorInstances.Add(newInstance);
             }
@@ -321,32 +326,43 @@ namespace Avalonia.Animation
         }
 
         /// <inheritdoc/>
-        public IDisposable Apply(Animatable control, IClock clock, IObservable<bool> match, Action onComplete)
+        public IDisposable Apply(Animatable control, IClock? clock, IObservable<bool> match, Action? onComplete)
         {
             var (animators, subscriptions) = InterpretKeyframes(control);
             if (animators.Count == 1)
             {
-                subscriptions.Add(animators[0].Apply(this, control, clock, match, onComplete));
+                var subscription = animators[0].Apply(this, control, clock, match, onComplete);
+                
+                if (subscription is not null)
+                {
+                    subscriptions.Add(subscription);
+                }
             }
             else
             {
                 var completionTasks = onComplete != null ? new List<Task>() : null;
                 foreach (IAnimator animator in animators)
                 {
-                    Action animatorOnComplete = null;
+                    Action? animatorOnComplete = null;
                     if (onComplete != null)
                     {
-                        var tcs = new TaskCompletionSource<object>();
+                        var tcs = new TaskCompletionSource<object?>();
                         animatorOnComplete = () => tcs.SetResult(null);
-                        completionTasks.Add(tcs.Task);
+                        completionTasks!.Add(tcs.Task);
+                    }
+
+                    var subscription = animator.Apply(this, control, clock, match, animatorOnComplete);
+
+                    if (subscription is not null)
+                    {
+                        subscriptions.Add(subscription);
                     }
-                    subscriptions.Add(animator.Apply(this, control, clock, match, animatorOnComplete));
                 }
 
                 if (onComplete != null)
                 {
-                    Task.WhenAll(completionTasks).ContinueWith(
-                        (_, state) => ((Action)state).Invoke(),
+                    Task.WhenAll(completionTasks!).ContinueWith(
+                        (_, state) => ((Action)state!).Invoke(),
                         onComplete);
                 }
             }
@@ -354,25 +370,25 @@ namespace Avalonia.Animation
         }
 
         /// <inheritdoc/>
-        public Task RunAsync(Animatable control, IClock clock = null)
+        public Task RunAsync(Animatable control, IClock? clock = null)
         {
             return RunAsync(control, clock, default);
         }
 
         /// <inheritdoc/>
-        public Task RunAsync(Animatable control, IClock clock = null, CancellationToken cancellationToken = default)
+        public Task RunAsync(Animatable control, IClock? clock = null, CancellationToken cancellationToken = default)
         {
             if (cancellationToken.IsCancellationRequested)
             {
                 return Task.CompletedTask;
             }
 
-            var run = new TaskCompletionSource<object>();
+            var run = new TaskCompletionSource<object?>();
 
             if (this.IterationCount == IterationCount.Infinite)
                 run.SetException(new InvalidOperationException("Looping animations must not use the Run method."));
 
-            IDisposable subscriptions = null, cancellation = null;
+            IDisposable? subscriptions = null, cancellation = null;
             subscriptions = this.Apply(control, clock, Observable.Return(true), () =>
             {
                 run.TrySetResult(null);
diff --git a/src/Avalonia.Animation/AnimationInstance`1.cs b/src/Avalonia.Animation/AnimationInstance`1.cs
index cf79640150..52cd4b324f 100644
--- a/src/Avalonia.Animation/AnimationInstance`1.cs
+++ b/src/Avalonia.Animation/AnimationInstance`1.cs
@@ -31,15 +31,15 @@ namespace Avalonia.Animation
         private TimeSpan _initialDelay;
         private TimeSpan _iterationDelay;
         private TimeSpan _duration;
-        private Easings.Easing _easeFunc;
-        private Action _onCompleteAction;
+        private Easings.Easing? _easeFunc;
+        private Action? _onCompleteAction;
         private Func<double, T, T> _interpolator;
-        private IDisposable _timerSub;
+        private IDisposable? _timerSub;
         private readonly IClock _baseClock;
-        private IClock _clock;
-        private EventHandler<AvaloniaPropertyChangedEventArgs> _propertyChangedDelegate;
+        private IClock? _clock;
+        private EventHandler<AvaloniaPropertyChangedEventArgs>? _propertyChangedDelegate;
 
-        public AnimationInstance(Animation animation, Animatable control, Animator<T> animator, IClock baseClock, Action OnComplete, Func<double, T, T> Interpolator)
+        public AnimationInstance(Animation animation, Animatable control, Animator<T> animator, IClock baseClock, Action? OnComplete, Func<double, T, T> Interpolator)
         {
             _animator = animator;
             _animation = animation;
@@ -47,6 +47,9 @@ namespace Avalonia.Animation
             _onCompleteAction = OnComplete;
             _interpolator = Interpolator;
             _baseClock = baseClock;
+            _lastInterpValue = default!;
+            _firstKFValue = default!;
+            _neutralValue = default!;
             FetchProperties();
         }
 
@@ -82,7 +85,7 @@ namespace Avalonia.Animation
 
             _targetControl.PropertyChanged -= _propertyChangedDelegate;
             _timerSub?.Dispose();
-            _clock.PlayState = PlayState.Stop;
+            _clock!.PlayState = PlayState.Stop;
         }
 
         protected override void Subscribed()
@@ -108,6 +111,8 @@ namespace Avalonia.Animation
 
         private void ApplyFinalFill()
         {
+            if (_animator.Property is null)
+                throw new InvalidOperationException("Animator has no property specified.");
             if (_fillMode == FillMode.Forward || _fillMode == FillMode.Both)
                 _targetControl.SetValue(_animator.Property, _lastInterpValue, BindingPriority.LocalValue);
         }
@@ -130,12 +135,12 @@ namespace Avalonia.Animation
 
         private void DoPlayStates()
         {
-            if (_clock.PlayState == PlayState.Stop || _baseClock.PlayState == PlayState.Stop)
+            if (_clock!.PlayState == PlayState.Stop || _baseClock.PlayState == PlayState.Stop)
                 DoComplete();
 
             if (!_gotFirstKFValue)
             {
-                _firstKFValue = (T)_animator.First().Value;
+                _firstKFValue = (T)_animator.First().Value!;
                 _gotFirstKFValue = true;
             }
         }
@@ -169,7 +174,7 @@ namespace Avalonia.Animation
                 // and snap the last iteration value to exact values.
                 if ((_currentIteration + 1) > _iterationCount)
                 {
-                    var easedTime = _easeFunc.Ease(_playbackReversed ? 0.0 : 1.0);
+                    var easedTime = _easeFunc!.Ease(_playbackReversed ? 0.0 : 1.0);
                     _lastInterpValue = _interpolator(easedTime, _neutralValue);
                     DoComplete();
                 }
@@ -203,7 +208,7 @@ namespace Avalonia.Animation
                         normalizedTime = 1 - normalizedTime;
 
                     // Ease and interpolate
-                    var easedTime = _easeFunc.Ease(normalizedTime);
+                    var easedTime = _easeFunc!.Ease(normalizedTime);
                     _lastInterpValue = _interpolator(easedTime, _neutralValue);
 
                     PublishNext(_lastInterpValue);
@@ -223,14 +228,14 @@ namespace Avalonia.Animation
 
         private void UpdateNeutralValue()
         {
-            var property = _animator.Property;
+            var property = _animator.Property ?? throw new InvalidOperationException("Animator has no property specified.");
             var baseValue = _targetControl.GetBaseValue(property, BindingPriority.LocalValue);
 
             _neutralValue = baseValue != AvaloniaProperty.UnsetValue ?
-                (T)baseValue : (T)_targetControl.GetValue(property);
+                (T)baseValue! : (T)_targetControl.GetValue(property)!;
         }
 
-        private void ControlPropertyChanged(object sender, AvaloniaPropertyChangedEventArgs e)
+        private void ControlPropertyChanged(object? sender, AvaloniaPropertyChangedEventArgs e)
         {
             if (e.Property == _animator.Property && e.Priority > BindingPriority.Animation)
             {
diff --git a/src/Avalonia.Animation/AnimatorKeyFrame.cs b/src/Avalonia.Animation/AnimatorKeyFrame.cs
index f6a0c12be4..8af31f2948 100644
--- a/src/Avalonia.Animation/AnimatorKeyFrame.cs
+++ b/src/Avalonia.Animation/AnimatorKeyFrame.cs
@@ -12,22 +12,22 @@ namespace Avalonia.Animation
     /// </summary>
     public class AnimatorKeyFrame : AvaloniaObject
     {
-        public static readonly DirectProperty<AnimatorKeyFrame, object> ValueProperty =
-            AvaloniaProperty.RegisterDirect<AnimatorKeyFrame, object>(nameof(Value), k => k.Value, (k, v) => k.Value = v);
+        public static readonly DirectProperty<AnimatorKeyFrame, object?> ValueProperty =
+            AvaloniaProperty.RegisterDirect<AnimatorKeyFrame, object?>(nameof(Value), k => k.Value, (k, v) => k.Value = v);
 
         public AnimatorKeyFrame()
         {
 
         }
 
-        public AnimatorKeyFrame(Type animatorType, Cue cue)
+        public AnimatorKeyFrame(Type? animatorType, Cue cue)
         {
             AnimatorType = animatorType;
             Cue = cue;
             KeySpline = null;
         }
 
-        public AnimatorKeyFrame(Type animatorType, Cue cue, KeySpline keySpline)
+        public AnimatorKeyFrame(Type? animatorType, Cue cue, KeySpline? keySpline)
         {
             AnimatorType = animatorType;
             Cue = cue;
@@ -35,14 +35,14 @@ namespace Avalonia.Animation
         }
 
         internal bool isNeutral;
-        public Type AnimatorType { get; }
+        public Type? AnimatorType { get; }
         public Cue Cue { get; }
-        public KeySpline KeySpline { get; }
-        public AvaloniaProperty Property { get; private set; }
+        public KeySpline? KeySpline { get; }
+        public AvaloniaProperty? Property { get; private set; }
 
-        private object _value;
+        private object? _value;
 
-        public object Value
+        public object? Value
         {
             get => _value;
             set => SetAndRaise(ValueProperty, ref _value, value);
@@ -80,7 +80,7 @@ namespace Avalonia.Animation
                 throw new InvalidCastException($"KeyFrame value doesnt match property type.");
             }
 
-            return (T)typeConv.ConvertTo(Value, typeof(T));
+            return (T)typeConv.ConvertTo(Value, typeof(T))!;
         }
     }
 }
diff --git a/src/Avalonia.Animation/Animators/Animator`1.cs b/src/Avalonia.Animation/Animators/Animator`1.cs
index 23afa76bf6..248ca61c1d 100644
--- a/src/Avalonia.Animation/Animators/Animator`1.cs
+++ b/src/Avalonia.Animation/Animators/Animator`1.cs
@@ -24,7 +24,7 @@ namespace Avalonia.Animation.Animators
         /// <summary>
         /// Gets or sets the target property for the keyframe.
         /// </summary>
-        public AvaloniaProperty Property { get; set; }
+        public AvaloniaProperty? Property { get; set; }
 
         public Animator()
         {
@@ -33,7 +33,7 @@ namespace Avalonia.Animation.Animators
         }
 
         /// <inheritdoc/>
-        public virtual IDisposable Apply(Animation animation, Animatable control, IClock clock, IObservable<bool> match, Action onComplete)
+        public virtual IDisposable? Apply(Animation animation, Animatable control, IClock? clock, IObservable<bool> match, Action? onComplete)
         {
             if (!_isVerifiedAndConverted)
                 VerifyConvertKeyFrames();
@@ -106,13 +106,16 @@ namespace Avalonia.Animation.Animators
 
         public virtual IDisposable BindAnimation(Animatable control, IObservable<T> instance)
         {
+            if (Property is null)
+                throw new InvalidOperationException("Animator has no property specified.");
+
             return control.Bind((AvaloniaProperty<T>)Property, instance, BindingPriority.Animation);
         }
 
         /// <summary>
         /// Runs the KeyFrames Animation.
         /// </summary>
-        internal IDisposable Run(Animation animation, Animatable control, IClock clock, Action onComplete)
+        internal IDisposable Run(Animation animation, Animatable control, IClock? clock, Action? onComplete)
         {
             var instance = new AnimationInstance<T>(
                 animation,
diff --git a/src/Avalonia.Animation/Avalonia.Animation.csproj b/src/Avalonia.Animation/Avalonia.Animation.csproj
index 465b922b72..d81d14bbff 100644
--- a/src/Avalonia.Animation/Avalonia.Animation.csproj
+++ b/src/Avalonia.Animation/Avalonia.Animation.csproj
@@ -2,9 +2,13 @@
   <PropertyGroup>
     <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
   </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="..\Avalonia.Base\Metadata\NullableAttributes.cs" Link="NullableAttributes.cs" />
+  </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\Avalonia.Base\Avalonia.Base.csproj" />
   </ItemGroup>
   <Import Project="..\..\build\Rx.props" />
   <Import Project="..\..\build\ApiDiff.props" />
+  <Import Project="..\..\build\NullableEnable.props" />
 </Project>
diff --git a/src/Avalonia.Animation/Clock.cs b/src/Avalonia.Animation/Clock.cs
index 5c2b7ce0dd..5afd2ae705 100644
--- a/src/Avalonia.Animation/Clock.cs
+++ b/src/Avalonia.Animation/Clock.cs
@@ -4,7 +4,7 @@ namespace Avalonia.Animation
 {
     public class Clock : ClockBase
     {
-        public static IClock GlobalClock => AvaloniaLocator.Current.GetService<IGlobalClock>();
+        public static IClock GlobalClock => AvaloniaLocator.Current.GetRequiredService<IGlobalClock>();
 
         private readonly IDisposable _parentSubscription;
 
diff --git a/src/Avalonia.Animation/Cue.cs b/src/Avalonia.Animation/Cue.cs
index 7da7a9382b..6578148b07 100644
--- a/src/Avalonia.Animation/Cue.cs
+++ b/src/Avalonia.Animation/Cue.cs
@@ -30,7 +30,7 @@ namespace Avalonia.Animation
         /// <summary>
         /// Parses a string to a <see cref="Cue"/> object.
         /// </summary>
-        public static Cue Parse(string value, CultureInfo culture)
+        public static Cue Parse(string value, CultureInfo? culture)
         {
             string v = value;
 
@@ -72,14 +72,14 @@ namespace Avalonia.Animation
 
     public class CueTypeConverter : TypeConverter
     {
-        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
+        public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
         {
             return sourceType == typeof(string);
         }
 
-        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+        public override object ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             return Cue.Parse((string)value, culture);
         }
     }
-}
\ No newline at end of file
+}
diff --git a/src/Avalonia.Animation/DisposeAnimationInstanceSubject.cs b/src/Avalonia.Animation/DisposeAnimationInstanceSubject.cs
index 696f43d006..7283eaeedf 100644
--- a/src/Avalonia.Animation/DisposeAnimationInstanceSubject.cs
+++ b/src/Avalonia.Animation/DisposeAnimationInstanceSubject.cs
@@ -8,15 +8,15 @@ namespace Avalonia.Animation
     /// </summary>
     internal class DisposeAnimationInstanceSubject<T> : IObserver<bool>, IDisposable
     {
-        private IDisposable _lastInstance;
+        private IDisposable? _lastInstance;
         private bool _lastMatch;
         private Animator<T> _animator;
         private Animation _animation;
         private Animatable _control;
-        private Action _onComplete;
-        private IClock _clock;
+        private Action? _onComplete;
+        private IClock? _clock;
 
-        public DisposeAnimationInstanceSubject(Animator<T> animator, Animation animation, Animatable control, IClock clock, Action onComplete)
+        public DisposeAnimationInstanceSubject(Animator<T> animator, Animation animation, Animatable control, IClock? clock, Action? onComplete)
         {
             this._animator = animator;
             this._animation = animation;
diff --git a/src/Avalonia.Animation/Easing/Easing.cs b/src/Avalonia.Animation/Easing/Easing.cs
index e006459652..2f4b93dab1 100644
--- a/src/Avalonia.Animation/Easing/Easing.cs
+++ b/src/Avalonia.Animation/Easing/Easing.cs
@@ -15,7 +15,7 @@ namespace Avalonia.Animation.Easings
         /// <inheritdoc/>
         public abstract double Ease(double progress);
 
-        static Dictionary<string, Type> _easingTypes;
+        static Dictionary<string, Type>? _easingTypes;
 
         static readonly Type s_thisType = typeof(Easing);
 
@@ -48,7 +48,7 @@ namespace Avalonia.Animation.Easings
             if (_easingTypes.ContainsKey(e))
             {
                 var type = _easingTypes[e];
-                return (Easing)Activator.CreateInstance(type);
+                return (Easing)Activator.CreateInstance(type)!;
             }
             else
             {
diff --git a/src/Avalonia.Animation/Easing/EasingTypeConverter.cs b/src/Avalonia.Animation/Easing/EasingTypeConverter.cs
index 6613f6d393..3d67d54a6f 100644
--- a/src/Avalonia.Animation/Easing/EasingTypeConverter.cs
+++ b/src/Avalonia.Animation/Easing/EasingTypeConverter.cs
@@ -6,12 +6,12 @@ namespace Avalonia.Animation.Easings
 {
     public class EasingTypeConverter : TypeConverter
     {
-        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
+        public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
         {
             return sourceType == typeof(string);
         }
 
-        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+        public override object ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             return Easing.Parse((string)value);
         }
diff --git a/src/Avalonia.Animation/IAnimation.cs b/src/Avalonia.Animation/IAnimation.cs
index d037834630..436a765d27 100644
--- a/src/Avalonia.Animation/IAnimation.cs
+++ b/src/Avalonia.Animation/IAnimation.cs
@@ -12,7 +12,7 @@ namespace Avalonia.Animation
         /// <summary>
         /// Apply the animation to the specified control and run it when <paramref name="match" /> produces <c>true</c>.
         /// </summary>
-        IDisposable Apply(Animatable control, IClock clock, IObservable<bool> match, Action onComplete = null);
+        IDisposable Apply(Animatable control, IClock? clock, IObservable<bool> match, Action? onComplete = null);
 
         /// <summary>
         /// Run the animation on the specified control.
diff --git a/src/Avalonia.Animation/IAnimationSetter.cs b/src/Avalonia.Animation/IAnimationSetter.cs
index 2d22377286..6a1d3539e2 100644
--- a/src/Avalonia.Animation/IAnimationSetter.cs
+++ b/src/Avalonia.Animation/IAnimationSetter.cs
@@ -2,7 +2,7 @@ namespace Avalonia.Animation
 {
     public interface IAnimationSetter
     {
-        AvaloniaProperty Property { get; set; }
-        object Value { get; set; }
+        AvaloniaProperty? Property { get; set; }
+        object? Value { get; set; }
     }
 }
diff --git a/src/Avalonia.Animation/IAnimator.cs b/src/Avalonia.Animation/IAnimator.cs
index d0fb173c54..f64ac9f913 100644
--- a/src/Avalonia.Animation/IAnimator.cs
+++ b/src/Avalonia.Animation/IAnimator.cs
@@ -11,11 +11,11 @@ namespace Avalonia.Animation
         /// <summary>
         /// The target property.
         /// </summary>
-        AvaloniaProperty Property {get; set;}
+        AvaloniaProperty? Property {get; set;}
 
         /// <summary>
         /// Applies the current KeyFrame group to the specified control.
         /// </summary>
-        IDisposable Apply(Animation animation, Animatable control, IClock clock, IObservable<bool> match, Action onComplete);
+        IDisposable? Apply(Animation animation, Animatable control, IClock? clock, IObservable<bool> match, Action? onComplete);
     }
 }
diff --git a/src/Avalonia.Animation/ITransition.cs b/src/Avalonia.Animation/ITransition.cs
index ade2ec8b9e..241ca208d1 100644
--- a/src/Avalonia.Animation/ITransition.cs
+++ b/src/Avalonia.Animation/ITransition.cs
@@ -10,7 +10,7 @@ namespace Avalonia.Animation
         /// <summary>
         /// Applies the transition to the specified <see cref="Animatable"/>.
         /// </summary>
-        IDisposable Apply(Animatable control, IClock clock, object oldValue, object newValue);
+        IDisposable Apply(Animatable control, IClock clock, object? oldValue, object? newValue);
 
         /// <summary>
         /// Gets the property to be animated.
diff --git a/src/Avalonia.Animation/IterationCount.cs b/src/Avalonia.Animation/IterationCount.cs
index 9463718608..3b52cdab49 100644
--- a/src/Avalonia.Animation/IterationCount.cs
+++ b/src/Avalonia.Animation/IterationCount.cs
@@ -97,7 +97,7 @@ namespace Avalonia.Animation
         /// </summary>
         /// <param name="o">The object with which to test equality.</param>
         /// <returns>True if the objects are equal, otherwise false.</returns>
-        public override bool Equals(object o)
+        public override bool Equals(object? o)
         {
             if (o == null)
             {
diff --git a/src/Avalonia.Animation/IterationCountTypeConverter.cs b/src/Avalonia.Animation/IterationCountTypeConverter.cs
index 1c63f8cdf1..f64972ff5c 100644
--- a/src/Avalonia.Animation/IterationCountTypeConverter.cs
+++ b/src/Avalonia.Animation/IterationCountTypeConverter.cs
@@ -6,12 +6,12 @@ namespace Avalonia.Animation
 {
     public class IterationCountTypeConverter : TypeConverter
     {
-        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
+        public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
         {
             return sourceType == typeof(string);
         }
 
-        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+        public override object ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             return IterationCount.Parse((string)value);
         }
diff --git a/src/Avalonia.Animation/KeyFrame.cs b/src/Avalonia.Animation/KeyFrame.cs
index c2cc1aa051..3ab7a70d90 100644
--- a/src/Avalonia.Animation/KeyFrame.cs
+++ b/src/Avalonia.Animation/KeyFrame.cs
@@ -19,7 +19,7 @@ namespace Avalonia.Animation
     {
         private TimeSpan _ktimeSpan;
         private Cue _kCue;
-        private KeySpline _kKeySpline;
+        private KeySpline? _kKeySpline;
 
         public KeyFrame()
         {
@@ -79,7 +79,7 @@ namespace Avalonia.Animation
         /// Gets or sets the KeySpline of this <see cref="KeyFrame"/>.
         /// </summary>
         /// <value>The key spline.</value>
-        public KeySpline KeySpline
+        public KeySpline? KeySpline
         {
             get
             {
diff --git a/src/Avalonia.Animation/KeySplineTypeConverter.cs b/src/Avalonia.Animation/KeySplineTypeConverter.cs
index b026206e5f..eecad3c3ac 100644
--- a/src/Avalonia.Animation/KeySplineTypeConverter.cs
+++ b/src/Avalonia.Animation/KeySplineTypeConverter.cs
@@ -12,12 +12,12 @@ namespace Avalonia.Animation
     /// </summary>
     public class KeySplineTypeConverter : TypeConverter
     {
-        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
+        public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
         {
             return sourceType == typeof(string);
         }
 
-        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+        public override object ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             return KeySpline.Parse((string)value, CultureInfo.InvariantCulture);
         }
diff --git a/src/Avalonia.Animation/Transition.cs b/src/Avalonia.Animation/Transition.cs
index 4115c95c0f..d307f348c4 100644
--- a/src/Avalonia.Animation/Transition.cs
+++ b/src/Avalonia.Animation/Transition.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Diagnostics.CodeAnalysis;
 using Avalonia.Animation.Easings;
 
 namespace Avalonia.Animation
@@ -8,7 +9,7 @@ namespace Avalonia.Animation
     /// </summary>
     public abstract class Transition<T> : AvaloniaObject, ITransition
     {
-        private AvaloniaProperty _prop;
+        private AvaloniaProperty? _prop;
 
         /// <summary>
         /// Gets or sets the duration of the transition.
@@ -26,7 +27,8 @@ namespace Avalonia.Animation
         public Easing Easing { get; set; } = new LinearEasing();
 
         /// <inheritdocs/>
-        public AvaloniaProperty Property
+        [DisallowNull]
+        public AvaloniaProperty? Property
         {
             get
             {
@@ -42,16 +44,25 @@ namespace Avalonia.Animation
             }
         }
 
+        AvaloniaProperty ITransition.Property
+        {
+            get => Property ?? throw new InvalidOperationException("Transition has no property specified.");
+            set => Property = value;
+        }
+
         /// <summary>
         /// Apply interpolation to the property.
         /// </summary>
         public abstract IObservable<T> DoTransition(IObservable<double> progress, T oldValue, T newValue);
 
         /// <inheritdocs/>
-        public virtual IDisposable Apply(Animatable control, IClock clock, object oldValue, object newValue)
+        public virtual IDisposable Apply(Animatable control, IClock clock, object? oldValue, object? newValue)
         {
-            var transition = DoTransition(new TransitionInstance(clock, Delay, Duration), (T)oldValue, (T)newValue);
+            if (Property is null)
+                throw new InvalidOperationException("Transition has no property specified.");
+
+            var transition = DoTransition(new TransitionInstance(clock, Delay, Duration), (T)oldValue!, (T)newValue!);
             return control.Bind<T>((AvaloniaProperty<T>)Property, transition, Data.BindingPriority.Animation);
         }
     }
-}
\ No newline at end of file
+}
diff --git a/src/Avalonia.Animation/TransitionInstance.cs b/src/Avalonia.Animation/TransitionInstance.cs
index b522d1961e..9c9494ff87 100644
--- a/src/Avalonia.Animation/TransitionInstance.cs
+++ b/src/Avalonia.Animation/TransitionInstance.cs
@@ -10,11 +10,11 @@ namespace Avalonia.Animation
     /// </summary>
     internal class TransitionInstance : SingleSubscriberObservableBase<double>, IObserver<TimeSpan>
     {
-        private IDisposable _timerSubscription;
+        private IDisposable? _timerSubscription;
         private TimeSpan _delay;
         private TimeSpan _duration;
         private readonly IClock _baseClock;
-        private TransitionClock _clock;
+        private TransitionClock? _clock;
 
         public TransitionInstance(IClock clock, TimeSpan delay, TimeSpan duration)
         {
@@ -67,7 +67,7 @@ namespace Avalonia.Animation
         protected override void Unsubscribed()
         {
             _timerSubscription?.Dispose();
-            _clock.PlayState = PlayState.Stop;
+            _clock!.PlayState = PlayState.Stop;
         }
 
         protected override void Subscribed()
diff --git a/src/Avalonia.Base/Collections/NotifyCollectionChangedExtensions.cs b/src/Avalonia.Base/Collections/NotifyCollectionChangedExtensions.cs
index dcd32ddd76..689fcc89a4 100644
--- a/src/Avalonia.Base/Collections/NotifyCollectionChangedExtensions.cs
+++ b/src/Avalonia.Base/Collections/NotifyCollectionChangedExtensions.cs
@@ -59,7 +59,7 @@ namespace Avalonia.Collections
         }
 
         private class WeakCollectionChangedObservable : LightweightObservableBase<NotifyCollectionChangedEventArgs>,
-            IWeakSubscriber<NotifyCollectionChangedEventArgs>
+            IWeakEventSubscriber<NotifyCollectionChangedEventArgs>
         {
             private WeakReference<INotifyCollectionChanged> _sourceReference;
 
@@ -68,31 +68,22 @@ namespace Avalonia.Collections
                 _sourceReference = source;
             }
 
-            public void OnEvent(object? sender, NotifyCollectionChangedEventArgs e)
+            public void OnEvent(object? sender,
+                WeakEvent ev,
+                NotifyCollectionChangedEventArgs e)
             {
                 PublishNext(e);
             }
-
             protected override void Initialize()
             {
                 if (_sourceReference.TryGetTarget(out var instance))
-                {
-                    WeakSubscriptionManager.Subscribe(
-                    instance,
-                    nameof(instance.CollectionChanged),
-                    this);
-                }
+                    WeakEvents.CollectionChanged.Subscribe(instance, this);
             }
 
             protected override void Deinitialize()
             {
                 if (_sourceReference.TryGetTarget(out var instance))
-                {
-                    WeakSubscriptionManager.Unsubscribe(
-                        instance,
-                        nameof(instance.CollectionChanged),
-                        this);
-                }
+                    WeakEvents.CollectionChanged.Unsubscribe(instance, this);
             }
         }
     }
diff --git a/src/Avalonia.Base/Data/Core/IndexerNodeBase.cs b/src/Avalonia.Base/Data/Core/IndexerNodeBase.cs
index e197e29103..a808827896 100644
--- a/src/Avalonia.Base/Data/Core/IndexerNodeBase.cs
+++ b/src/Avalonia.Base/Data/Core/IndexerNodeBase.cs
@@ -23,18 +23,16 @@ namespace Avalonia.Data.Core
 
             if (incc != null)
             {
-                inputs.Add(WeakObservable.FromEventPattern<INotifyCollectionChanged, NotifyCollectionChangedEventArgs>(
-                    incc,
-                    nameof(incc.CollectionChanged))
+                inputs.Add(WeakObservable.FromEventPattern(
+                    incc, WeakEvents.CollectionChanged)
                     .Where(x => ShouldUpdate(x.Sender, x.EventArgs))
                     .Select(_ => GetValue(target)));
             }
 
             if (inpc != null)
             {
-                inputs.Add(WeakObservable.FromEventPattern<INotifyPropertyChanged, PropertyChangedEventArgs>(
-                    inpc,
-                    nameof(inpc.PropertyChanged))
+                inputs.Add(WeakObservable.FromEventPattern(
+                    inpc, WeakEvents.PropertyChanged)
                     .Where(x => ShouldUpdate(x.Sender, x.EventArgs))
                     .Select(_ => GetValue(target)));
             }
diff --git a/src/Avalonia.Base/Data/Core/Plugins/IndeiValidationPlugin.cs b/src/Avalonia.Base/Data/Core/Plugins/IndeiValidationPlugin.cs
index 9f827daf94..1e7a0d5c8f 100644
--- a/src/Avalonia.Base/Data/Core/Plugins/IndeiValidationPlugin.cs
+++ b/src/Avalonia.Base/Data/Core/Plugins/IndeiValidationPlugin.cs
@@ -11,6 +11,12 @@ namespace Avalonia.Data.Core.Plugins
     /// </summary>
     public class IndeiValidationPlugin : IDataValidationPlugin
     {
+        private static readonly WeakEvent<INotifyDataErrorInfo, DataErrorsChangedEventArgs>
+            ErrorsChangedWeakEvent = WeakEvent.Register<INotifyDataErrorInfo, DataErrorsChangedEventArgs>(
+                (s, h) => s.ErrorsChanged += h,
+                (s, h) => s.ErrorsChanged -= h
+            );
+
         /// <inheritdoc/>
         public bool Match(WeakReference<object?> reference, string memberName)
         {
@@ -25,7 +31,7 @@ namespace Avalonia.Data.Core.Plugins
             return new Validator(reference, name, accessor);
         }
 
-        private class Validator : DataValidationBase, IWeakSubscriber<DataErrorsChangedEventArgs>
+        private class Validator : DataValidationBase, IWeakEventSubscriber<DataErrorsChangedEventArgs>
         {
             private readonly WeakReference<object?> _reference;
             private readonly string _name;
@@ -37,7 +43,7 @@ namespace Avalonia.Data.Core.Plugins
                 _name = name;
             }
 
-            void IWeakSubscriber<DataErrorsChangedEventArgs>.OnEvent(object? sender, DataErrorsChangedEventArgs e)
+            void IWeakEventSubscriber<DataErrorsChangedEventArgs>.OnEvent(object? notifyDataErrorInfo, WeakEvent ev, DataErrorsChangedEventArgs e)
             {
                 if (e.PropertyName == _name || string.IsNullOrEmpty(e.PropertyName))
                 {
@@ -51,10 +57,7 @@ namespace Avalonia.Data.Core.Plugins
 
                 if (target != null)
                 {
-                    WeakSubscriptionManager.Subscribe(
-                        target,
-                        nameof(target.ErrorsChanged),
-                        this);
+                    ErrorsChangedWeakEvent.Subscribe(target, this);
                 }
 
                 base.SubscribeCore();
@@ -66,10 +69,7 @@ namespace Avalonia.Data.Core.Plugins
 
                 if (target != null)
                 {
-                    WeakSubscriptionManager.Unsubscribe(
-                        target,
-                        nameof(target.ErrorsChanged),
-                        this);
+                    ErrorsChangedWeakEvent.Unsubscribe(target, this);
                 }
 
                 base.UnsubscribeCore();
diff --git a/src/Avalonia.Base/Data/Core/Plugins/InpcPropertyAccessorPlugin.cs b/src/Avalonia.Base/Data/Core/Plugins/InpcPropertyAccessorPlugin.cs
index fd532f3014..33cecd10a7 100644
--- a/src/Avalonia.Base/Data/Core/Plugins/InpcPropertyAccessorPlugin.cs
+++ b/src/Avalonia.Base/Data/Core/Plugins/InpcPropertyAccessorPlugin.cs
@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Collections.Specialized;
 using System.ComponentModel;
 using System.Reflection;
 using Avalonia.Utilities;
@@ -85,7 +86,7 @@ namespace Avalonia.Data.Core.Plugins
             return found;
         }
 
-        private class Accessor : PropertyAccessorBase, IWeakSubscriber<PropertyChangedEventArgs>
+        private class Accessor : PropertyAccessorBase, IWeakEventSubscriber<PropertyChangedEventArgs>
         {
             private readonly WeakReference<object?> _reference;
             private readonly PropertyInfo _property;
@@ -129,7 +130,8 @@ namespace Avalonia.Data.Core.Plugins
                 return false;
             }
 
-            void IWeakSubscriber<PropertyChangedEventArgs>.OnEvent(object? sender, PropertyChangedEventArgs e)
+            void IWeakEventSubscriber<PropertyChangedEventArgs>.
+                OnEvent(object? notifyPropertyChanged, WeakEvent ev, PropertyChangedEventArgs e)
             {
                 if (e.PropertyName == _property.Name || string.IsNullOrEmpty(e.PropertyName))
                 {
@@ -148,13 +150,8 @@ namespace Avalonia.Data.Core.Plugins
             {
                 var inpc = GetReferenceTarget() as INotifyPropertyChanged;
 
-                if (inpc != null)
-                {
-                    WeakSubscriptionManager.Unsubscribe(
-                        inpc,
-                        nameof(inpc.PropertyChanged),
-                        this);
-                }
+                if (inpc != null) 
+                    WeakEvents.PropertyChanged.Unsubscribe(inpc, this);
             }
 
             private object? GetReferenceTarget()
@@ -178,13 +175,8 @@ namespace Avalonia.Data.Core.Plugins
             {
                 var inpc = GetReferenceTarget() as INotifyPropertyChanged;
 
-                if (inpc != null)
-                {
-                    WeakSubscriptionManager.Subscribe(
-                        inpc,
-                        nameof(inpc.PropertyChanged),
-                        this);
-                }
+                if (inpc != null) 
+                    WeakEvents.PropertyChanged.Subscribe(inpc, this);
             }
         }
     }
diff --git a/src/Avalonia.Base/Utilities/IWeakEventSubscriber.cs b/src/Avalonia.Base/Utilities/IWeakEventSubscriber.cs
new file mode 100644
index 0000000000..e48c0cb111
--- /dev/null
+++ b/src/Avalonia.Base/Utilities/IWeakEventSubscriber.cs
@@ -0,0 +1,12 @@
+using System;
+
+namespace Avalonia.Utilities;
+
+/// <summary>
+/// Defines a listener to a event subscribed vis the <see cref="WeakEvent{TTarget, TEventArgs}"/>.
+/// </summary>
+/// <typeparam name="TEventArgs">The type of the event arguments.</typeparam>
+public interface IWeakEventSubscriber<in TEventArgs> where TEventArgs : EventArgs
+{
+    void OnEvent(object? sender, WeakEvent ev, TEventArgs e);
+}
\ No newline at end of file
diff --git a/src/Avalonia.Base/Utilities/WeakEvent.cs b/src/Avalonia.Base/Utilities/WeakEvent.cs
new file mode 100644
index 0000000000..0b32015a8a
--- /dev/null
+++ b/src/Avalonia.Base/Utilities/WeakEvent.cs
@@ -0,0 +1,187 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+using System.Runtime.CompilerServices;
+using Avalonia.Threading;
+
+namespace Avalonia.Utilities;
+
+/// <summary>
+/// Manages subscriptions to events using weak listeners.
+/// </summary>
+public class WeakEvent<TSender, TEventArgs> : WeakEvent where TEventArgs : EventArgs where TSender : class
+{
+    private readonly Func<TSender, EventHandler<TEventArgs>, Action> _subscribe;
+
+    readonly ConditionalWeakTable<object, Subscription> _subscriptions = new();
+
+    internal WeakEvent(
+        Action<TSender, EventHandler<TEventArgs>> subscribe,
+        Action<TSender, EventHandler<TEventArgs>> unsubscribe)
+    {
+        _subscribe = (t, s) =>
+        {
+            subscribe(t, s);
+            return () => unsubscribe(t, s);
+        };
+    }
+    
+    internal WeakEvent(Func<TSender, EventHandler<TEventArgs>, Action> subscribe)
+    {
+        _subscribe = subscribe;
+    }
+    
+    public void Subscribe(TSender target, IWeakEventSubscriber<TEventArgs> subscriber)
+    {
+        if (!_subscriptions.TryGetValue(target, out var subscription))
+            _subscriptions.Add(target, subscription = new Subscription(this, target));
+        subscription.Add(new WeakReference<IWeakEventSubscriber<TEventArgs>>(subscriber));
+    }
+
+    public void Unsubscribe(TSender target, IWeakEventSubscriber<TEventArgs> subscriber)
+    {
+        if (_subscriptions.TryGetValue(target, out var subscription)) 
+            subscription.Remove(subscriber);
+    }
+
+    private class Subscription
+    {
+        private readonly WeakEvent<TSender, TEventArgs> _ev;
+        private readonly TSender _target;
+        private readonly Action _compact;
+
+        private WeakReference<IWeakEventSubscriber<TEventArgs>>?[] _data =
+            new WeakReference<IWeakEventSubscriber<TEventArgs>>[16];
+        private int _count;
+        private readonly Action _unsubscribe;
+        private bool _compactScheduled;
+
+        public Subscription(WeakEvent<TSender, TEventArgs> ev, TSender target)
+        {
+            _ev = ev;
+            _target = target;
+            _compact = Compact;
+            _unsubscribe = ev._subscribe(target, OnEvent);
+        }
+
+        void Destroy()
+        {
+            _unsubscribe();
+            _ev._subscriptions.Remove(_target);
+        }
+
+        public void Add(WeakReference<IWeakEventSubscriber<TEventArgs>> s)
+        {
+            if (_count == _data.Length)
+            {
+                //Extend capacity
+                var extendedData = new WeakReference<IWeakEventSubscriber<TEventArgs>>?[_data.Length * 2];
+                Array.Copy(_data, extendedData, _data.Length);
+                _data = extendedData;
+            }
+
+            _data[_count] = s;
+            _count++;
+        }
+
+        public void Remove(IWeakEventSubscriber<TEventArgs> s)
+        {
+            var removed = false;
+
+            for (int c = 0; c < _count; ++c)
+            {
+                var reference = _data[c];
+
+                if (reference != null && reference.TryGetTarget(out var instance) && instance == s)
+                {
+                    _data[c] = null;
+                    removed = true;
+                }
+            }
+
+            if (removed)
+            {
+                ScheduleCompact();
+            }
+        }
+
+        void ScheduleCompact()
+        {
+            if(_compactScheduled)
+                return;
+            _compactScheduled = true;
+            Dispatcher.UIThread.Post(_compact, DispatcherPriority.Background);
+        }
+        
+        void Compact()
+        {
+            _compactScheduled = false;
+            int empty = -1;
+            for (var c = 0; c < _count; c++)
+            {
+                var r = _data[c];
+                //Mark current index as first empty
+                if (r == null && empty == -1)
+                    empty = c;
+                //If current element isn't null and we have an empty one
+                if (r != null && empty != -1)
+                {
+                    _data[c] = null;
+                    _data[empty] = r;
+                    empty++;
+                }
+            }
+
+            if (empty != -1)
+                _count = empty;
+            if (_count == 0)
+                Destroy();
+        }
+
+        void OnEvent(object? sender, TEventArgs eventArgs)
+        {
+            var needCompact = false;
+            for (var c = 0; c < _count; c++)
+            {
+                var r = _data[c];
+                if (r?.TryGetTarget(out var sub) == true)
+                    sub!.OnEvent(_target, _ev, eventArgs);
+                else
+                    needCompact = true;
+            }
+
+            if (needCompact)
+                ScheduleCompact();
+        }
+    }
+
+}
+
+public class WeakEvent
+{
+    public static WeakEvent<TSender, TEventArgs> Register<TSender, TEventArgs>(
+        Action<TSender, EventHandler<TEventArgs>> subscribe,
+        Action<TSender, EventHandler<TEventArgs>> unsubscribe) where TSender : class where TEventArgs : EventArgs
+    {
+        return new WeakEvent<TSender, TEventArgs>(subscribe, unsubscribe);
+    }
+    
+    public static WeakEvent<TSender, TEventArgs> Register<TSender, TEventArgs>(
+        Func<TSender, EventHandler<TEventArgs>, Action> subscribe) where TSender : class where TEventArgs : EventArgs
+    {
+        return new WeakEvent<TSender, TEventArgs>(subscribe);
+    }
+    
+    public static WeakEvent<TSender, EventArgs> Register<TSender>(
+        Action<TSender, EventHandler> subscribe,
+        Action<TSender, EventHandler> unsubscribe) where TSender : class
+    {
+        return Register<TSender, EventArgs>((s, h) =>
+        {
+            EventHandler handler = (_, e) => h(s, e);
+            subscribe(s, handler);
+            return () => unsubscribe(s, handler);
+        });
+    }
+}
\ No newline at end of file
diff --git a/src/Avalonia.Base/Utilities/WeakEvents.cs b/src/Avalonia.Base/Utilities/WeakEvents.cs
new file mode 100644
index 0000000000..d1b5e7f12d
--- /dev/null
+++ b/src/Avalonia.Base/Utilities/WeakEvents.cs
@@ -0,0 +1,40 @@
+using System;
+using System.Collections.Specialized;
+using System.ComponentModel;
+using System.Windows.Input;
+
+namespace Avalonia.Utilities;
+
+public class WeakEvents
+{
+    /// <summary>
+    /// Represents CollectionChanged event from <see cref="INotifyCollectionChanged"/>
+    /// </summary>
+    public static readonly WeakEvent<INotifyCollectionChanged, NotifyCollectionChangedEventArgs>
+        CollectionChanged = WeakEvent.Register<INotifyCollectionChanged, NotifyCollectionChangedEventArgs>(
+            (c, s) =>
+            {
+                NotifyCollectionChangedEventHandler handler = (_, e) => s(c, e);
+                c.CollectionChanged += handler;
+                return () => c.CollectionChanged -= handler;
+            });
+    
+    /// <summary>
+    /// Represents PropertyChanged event from <see cref="INotifyPropertyChanged"/>
+    /// </summary>
+    public static readonly WeakEvent<INotifyPropertyChanged, PropertyChangedEventArgs>
+        PropertyChanged = WeakEvent.Register<INotifyPropertyChanged, PropertyChangedEventArgs>(
+            (s, h) =>
+            {
+                PropertyChangedEventHandler handler = (_, e) => h(s, e);
+                s.PropertyChanged += handler;
+                return () => s.PropertyChanged -= handler;
+            });
+
+    /// <summary>
+    /// Represents CanExecuteChanged event from <see cref="ICommand"/>
+    /// </summary>
+    public static readonly WeakEvent<ICommand, EventArgs> CommandCanExecuteChanged =
+        WeakEvent.Register<ICommand>((s, h) => s.CanExecuteChanged += h,
+            (s, h) => s.CanExecuteChanged -= h);
+}
\ No newline at end of file
diff --git a/src/Avalonia.Base/Utilities/WeakObservable.cs b/src/Avalonia.Base/Utilities/WeakObservable.cs
index 52edc7ad1a..6bf1d4082f 100644
--- a/src/Avalonia.Base/Utilities/WeakObservable.cs
+++ b/src/Avalonia.Base/Utilities/WeakObservable.cs
@@ -18,6 +18,7 @@ namespace Avalonia.Utilities
         /// <param name="target">Object instance that exposes the event to convert.</param>
         /// <param name="eventName">Name of the event to convert.</param>
         /// <returns></returns>
+        [Obsolete("Use WeakEvent-based overload")]
         public static IObservable<EventPattern<object, TEventArgs>> FromEventPattern<TTarget, TEventArgs>(
             TTarget target, 
             string eventName)
@@ -34,7 +35,9 @@ namespace Avalonia.Utilities
             }).Publish().RefCount();
         }
 
-        private class Handler<TEventArgs> : IWeakSubscriber<TEventArgs> where TEventArgs : EventArgs
+        private class Handler<TEventArgs> 
+            : IWeakSubscriber<TEventArgs>,
+                IWeakEventSubscriber<TEventArgs> where TEventArgs : EventArgs
         {
             private IObserver<EventPattern<object, TEventArgs>> _observer;
 
@@ -47,6 +50,36 @@ namespace Avalonia.Utilities
             {
                 _observer.OnNext(new EventPattern<object, TEventArgs>(sender, e));
             }
+
+            public void OnEvent(object? sender, WeakEvent ev, TEventArgs e)
+            {
+                _observer.OnNext(new EventPattern<object, TEventArgs>(sender, e));
+            }
         }
+        
+        /// <summary>
+        /// Converts a WeakEvent conforming to the standard .NET event pattern into an observable
+        /// sequence, subscribing weakly.
+        /// </summary>
+        /// <typeparam name="TTarget">The type of target.</typeparam>
+        /// <typeparam name="TEventArgs">The type of the event args.</typeparam>
+        /// <param name="target">Object instance that exposes the event to convert.</param>
+        /// <param name="ev">The weak event to convert.</param>
+        /// <returns></returns>
+        public static IObservable<EventPattern<object, TEventArgs>> FromEventPattern<TTarget, TEventArgs>(
+            TTarget target, WeakEvent<TTarget, TEventArgs> ev)
+            where TEventArgs : EventArgs where TTarget : class
+        {
+            _ = target ?? throw new ArgumentNullException(nameof(target));
+            _ = ev ?? throw new ArgumentNullException(nameof(ev));
+
+            return Observable.Create<EventPattern<object, TEventArgs>>(observer =>
+            {
+                var handler = new Handler<TEventArgs>(observer);
+                ev.Subscribe(target, handler);
+                return () => ev.Unsubscribe(target, handler);
+            }).Publish().RefCount();
+        }
+
     }
 }
diff --git a/src/Avalonia.Base/Utilities/WeakSubscriptionManager.cs b/src/Avalonia.Base/Utilities/WeakSubscriptionManager.cs
index 88b1e3c807..dc9e86cc32 100644
--- a/src/Avalonia.Base/Utilities/WeakSubscriptionManager.cs
+++ b/src/Avalonia.Base/Utilities/WeakSubscriptionManager.cs
@@ -19,6 +19,7 @@ namespace Avalonia.Utilities
         /// <param name="target">The event source.</param>
         /// <param name="eventName">The name of the event.</param>
         /// <param name="subscriber">The subscriber.</param>
+        [Obsolete("Use WeakEvent")]
         public static void Subscribe<TTarget, TEventArgs>(TTarget target, string eventName, IWeakSubscriber<TEventArgs> subscriber)
             where TEventArgs : EventArgs
         {
diff --git a/src/Avalonia.Controls.DataGrid/DataGrid.cs b/src/Avalonia.Controls.DataGrid/DataGrid.cs
index 10c7c16488..95ee73be4e 100644
--- a/src/Avalonia.Controls.DataGrid/DataGrid.cs
+++ b/src/Avalonia.Controls.DataGrid/DataGrid.cs
@@ -5751,6 +5751,7 @@ namespace Avalonia.Controls
                 return true;
             }
             // Unselect everything except the row that was clicked on
+            _noSelectionChangeCount++;
             try
             {
                 UpdateSelectionAndCurrency(columnIndex, slot, DataGridSelectionAction.SelectCurrent, scrollIntoView: false);
diff --git a/src/Avalonia.Controls.DataGrid/DataGridColumn.cs b/src/Avalonia.Controls.DataGrid/DataGridColumn.cs
index 6b515503aa..8501ce3896 100644
--- a/src/Avalonia.Controls.DataGrid/DataGridColumn.cs
+++ b/src/Avalonia.Controls.DataGrid/DataGridColumn.cs
@@ -448,7 +448,7 @@ namespace Avalonia.Controls
             internal set;
         }
 
-        public bool IsReadOnly
+        public virtual bool IsReadOnly
         {
             get
             {
diff --git a/src/Avalonia.Controls.DataGrid/DataGridTemplateColumn.cs b/src/Avalonia.Controls.DataGrid/DataGridTemplateColumn.cs
index 7e95dd100c..0e754d5815 100644
--- a/src/Avalonia.Controls.DataGrid/DataGridTemplateColumn.cs
+++ b/src/Avalonia.Controls.DataGrid/DataGridTemplateColumn.cs
@@ -1,4 +1,4 @@
-// (c) Copyright Microsoft Corporation.
+// (c) Copyright Microsoft Corporation.
 // This source is subject to the Microsoft Public License (Ms-PL).
 // Please see http://go.microsoft.com/fwlink/?LinkID=131993 for details.
 // All other rights reserved.
@@ -15,7 +15,7 @@ namespace Avalonia.Controls
 {
     public class DataGridTemplateColumn : DataGridColumn
     {
-        IDataTemplate _cellTemplate;
+        private IDataTemplate _cellTemplate;
 
         public static readonly DirectProperty<DataGridTemplateColumn, IDataTemplate> CellTemplateProperty =
             AvaloniaProperty.RegisterDirect<DataGridTemplateColumn, IDataTemplate>(
@@ -30,17 +30,38 @@ namespace Avalonia.Controls
             set { SetAndRaise(CellTemplateProperty, ref _cellTemplate, value); }
         }
 
+        private IDataTemplate _cellEditingCellTemplate;
+
+        /// <summary>
+        /// Defines the <see cref="CellEditingTemplate"/> property.
+        /// </summary>
+        public static readonly DirectProperty<DataGridTemplateColumn, IDataTemplate> CellEditingTemplateProperty =
+                AvaloniaProperty.RegisterDirect<DataGridTemplateColumn, IDataTemplate>(
+                    nameof(CellEditingTemplate),
+                    o => o.CellEditingTemplate,
+                    (o, v) => o.CellEditingTemplate = v);
+
+        /// <summary>
+        /// Gets or sets the <see cref="IDataTemplate"/> which is used for the editing mode of the current <see cref="DataGridCell"/>
+        /// </summary>
+        /// <value>
+        /// An <see cref="IDataTemplate"/> for the editing mode of the current <see cref="DataGridCell"/>
+        /// </value>
+        /// <remarks>
+        /// If this property is <see langword="null"/> the column is read-only.
+        /// </remarks>
+        public IDataTemplate CellEditingTemplate
+        {
+            get => _cellEditingCellTemplate;
+            set => SetAndRaise(CellEditingTemplateProperty, ref _cellEditingCellTemplate, value);
+        }
+        
         private void OnCellTemplateChanged(AvaloniaPropertyChangedEventArgs e)
         {
             var oldValue = (IDataTemplate)e.OldValue;
             var value = (IDataTemplate)e.NewValue;
         }
 
-        public DataGridTemplateColumn()
-        {
-            IsReadOnly = true;
-        }
-
         protected override IControl GenerateElement(DataGridCell cell, object dataItem)
         {
             if(CellTemplate != null)
@@ -60,7 +81,22 @@ namespace Avalonia.Controls
         protected override IControl GenerateEditingElement(DataGridCell cell, object dataItem, out ICellEditBinding binding)
         {
             binding = null;
-            return GenerateElement(cell, dataItem);
+            if(CellEditingTemplate != null)
+            {
+                return CellEditingTemplate.Build(dataItem);
+            }
+            else if (CellTemplate != null)
+            {
+                return CellTemplate.Build(dataItem);
+            }
+            if (Design.IsDesignMode)
+            {
+                return null;
+            }
+            else
+            {
+                throw DataGridError.DataGridTemplateColumn.MissingTemplateForType(typeof(DataGridTemplateColumn));
+            }
         }
 
         protected override object PrepareCellForEdit(IControl editingElement, RoutedEventArgs editingEventArgs)
@@ -70,12 +106,30 @@ namespace Avalonia.Controls
 
         protected internal override void RefreshCellContent(IControl element, string propertyName)
         {
-            if(propertyName == nameof(CellTemplate) && element.Parent is DataGridCell cell)
+            var cell = element.Parent as DataGridCell;
+            if(propertyName == nameof(CellTemplate) && cell is not null)
             {
                 cell.Content = GenerateElement(cell, cell.DataContext);
             }
 
             base.RefreshCellContent(element, propertyName);
         }
+        
+        public override bool IsReadOnly
+        {
+            get
+            {
+                if (CellEditingTemplate is null)
+                {
+                    return true;
+                }
+
+                return base.IsReadOnly;
+            }
+            set
+            {
+                base.IsReadOnly = value;
+            }
+        }
     }
 }
diff --git a/src/Avalonia.Controls/ApiCompatBaseline.txt b/src/Avalonia.Controls/ApiCompatBaseline.txt
index dd41c30e85..9b7d37e108 100644
--- a/src/Avalonia.Controls/ApiCompatBaseline.txt
+++ b/src/Avalonia.Controls/ApiCompatBaseline.txt
@@ -29,15 +29,20 @@ MembersMustExist : Member 'public void Avalonia.Controls.NumericUpDownValueChang
 MembersMustExist : Member 'public System.Double Avalonia.Controls.NumericUpDownValueChangedEventArgs.NewValue.get()' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public System.Double Avalonia.Controls.NumericUpDownValueChangedEventArgs.OldValue.get()' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public Avalonia.StyledProperty<System.Boolean> Avalonia.StyledProperty<System.Boolean> Avalonia.Controls.ScrollViewer.AllowAutoHideProperty' does not exist in the implementation but it does exist in the contract.
+CannotRemoveBaseTypeOrInterface : Type 'Avalonia.Controls.TopLevel' does not implement interface 'Avalonia.Utilities.IWeakSubscriber<Avalonia.Controls.ResourcesChangedEventArgs>' in the implementation but it does in the contract.
 MembersMustExist : Member 'public Avalonia.AvaloniaProperty<Avalonia.Media.Stretch> Avalonia.AvaloniaProperty<Avalonia.Media.Stretch> Avalonia.Controls.Viewbox.StretchProperty' does not exist in the implementation but it does exist in the contract.
+CannotRemoveBaseTypeOrInterface : Type 'Avalonia.Controls.Window' does not implement interface 'Avalonia.Utilities.IWeakSubscriber<Avalonia.Controls.ResourcesChangedEventArgs>' in the implementation but it does in the contract.
+CannotRemoveBaseTypeOrInterface : Type 'Avalonia.Controls.WindowBase' does not implement interface 'Avalonia.Utilities.IWeakSubscriber<Avalonia.Controls.ResourcesChangedEventArgs>' in the implementation but it does in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public System.EventHandler<Avalonia.Controls.ApplicationLifetimes.ShutdownRequestedEventArgs> Avalonia.Controls.ApplicationLifetimes.IClassicDesktopStyleApplicationLifetime.ShutdownRequested' is present in the implementation but not in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Controls.ApplicationLifetimes.IClassicDesktopStyleApplicationLifetime.add_ShutdownRequested(System.EventHandler<Avalonia.Controls.ApplicationLifetimes.ShutdownRequestedEventArgs>)' is present in the implementation but not in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Controls.ApplicationLifetimes.IClassicDesktopStyleApplicationLifetime.remove_ShutdownRequested(System.EventHandler<Avalonia.Controls.ApplicationLifetimes.ShutdownRequestedEventArgs>)' is present in the implementation but not in the contract.
+CannotRemoveBaseTypeOrInterface : Type 'Avalonia.Controls.Embedding.EmbeddableControlRoot' does not implement interface 'Avalonia.Utilities.IWeakSubscriber<Avalonia.Controls.ResourcesChangedEventArgs>' in the implementation but it does in the contract.
 MembersMustExist : Member 'public System.Action<Avalonia.Size> Avalonia.Controls.Embedding.Offscreen.OffscreenTopLevelImplBase.Resized.get()' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public void Avalonia.Controls.Embedding.Offscreen.OffscreenTopLevelImplBase.Resized.set(System.Action<Avalonia.Size>)' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public void Avalonia.Controls.Embedding.Offscreen.OffscreenTopLevelImplBase.SetCursor(Avalonia.Platform.IPlatformHandle)' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public Avalonia.AvaloniaProperty Avalonia.AvaloniaProperty Avalonia.Controls.Notifications.NotificationCard.CloseOnClickProperty' does not exist in the implementation but it does exist in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Controls.Platform.ITopLevelNativeMenuExporter.SetNativeMenu(Avalonia.Controls.NativeMenu)' is present in the contract but not in the implementation.
+CannotRemoveBaseTypeOrInterface : Type 'Avalonia.Controls.Primitives.PopupRoot' does not implement interface 'Avalonia.Utilities.IWeakSubscriber<Avalonia.Controls.ResourcesChangedEventArgs>' in the implementation but it does in the contract.
 EnumValuesMustMatch : Enum value 'Avalonia.Platform.ExtendClientAreaChromeHints Avalonia.Platform.ExtendClientAreaChromeHints.Default' is (System.Int32)2 in the implementation but (System.Int32)1 in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public System.Nullable<Avalonia.Size> Avalonia.Platform.ITopLevelImpl.FrameSize' is present in the implementation but not in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public System.Nullable<Avalonia.Size> Avalonia.Platform.ITopLevelImpl.FrameSize.get()' is present in the implementation but not in the contract.
@@ -57,4 +62,4 @@ InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Platfor
 MembersMustExist : Member 'public void Avalonia.Platform.IWindowImpl.Resize(Avalonia.Size)' does not exist in the implementation but it does exist in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Platform.IWindowImpl.Resize(Avalonia.Size, Avalonia.Platform.PlatformResizeReason)' is present in the implementation but not in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public Avalonia.Platform.ITrayIconImpl Avalonia.Platform.IWindowingPlatform.CreateTrayIcon()' is present in the implementation but not in the contract.
-Total Issues: 58
+Total Issues: 63
diff --git a/src/Avalonia.Controls/Calendar/CalendarDatePicker.cs b/src/Avalonia.Controls/Calendar/CalendarDatePicker.cs
index a856ee071c..cd9c80d3e0 100644
--- a/src/Avalonia.Controls/Calendar/CalendarDatePicker.cs
+++ b/src/Avalonia.Controls/Calendar/CalendarDatePicker.cs
@@ -185,7 +185,8 @@ namespace Avalonia.Controls
             AvaloniaProperty.RegisterDirect<CalendarDatePicker, DateTime?>(
                 nameof(SelectedDate),
                 o => o.SelectedDate,
-                (o, v) => o.SelectedDate = v);
+                (o, v) => o.SelectedDate = v,
+                enableDataValidation: true);
 
         public static readonly StyledProperty<CalendarDatePickerFormat> SelectedDateFormatProperty =
             AvaloniaProperty.Register<CalendarDatePicker, CalendarDatePickerFormat>(
@@ -533,13 +534,11 @@ namespace Avalonia.Controls
             }
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void UpdateDataValidation<T>(AvaloniaProperty<T> property, BindingValue<T> value)
         {
-            base.OnPropertyChanged(change);
-
-            if (change.Property == SelectedDateProperty)
+            if (property == SelectedDateProperty)
             {
-                DataValidationErrors.SetError(this, change.NewValue.Error);
+                DataValidationErrors.SetError(this, value.Error);
             }
         }
 
diff --git a/src/Avalonia.Controls/NativeMenuItem.cs b/src/Avalonia.Controls/NativeMenuItem.cs
index 2ceaeb6dba..4d048f0fb0 100644
--- a/src/Avalonia.Controls/NativeMenuItem.cs
+++ b/src/Avalonia.Controls/NativeMenuItem.cs
@@ -33,7 +33,7 @@ namespace Avalonia.Controls
         }
 
 
-        class CanExecuteChangedSubscriber : IWeakSubscriber<EventArgs>
+        class CanExecuteChangedSubscriber : IWeakEventSubscriber<EventArgs>
         {
             private readonly NativeMenuItem _parent;
 
@@ -42,7 +42,7 @@ namespace Avalonia.Controls
                 _parent = parent;
             }
 
-            public void OnEvent(object sender, EventArgs e)
+            public void OnEvent(object? sender, WeakEvent ev, EventArgs e)
             {
                 _parent.CanExecuteChanged();
             }
@@ -160,14 +160,12 @@ namespace Avalonia.Controls
             set
             {
                 if (_command != null)
-                    WeakSubscriptionManager.Unsubscribe(_command,
-                        nameof(ICommand.CanExecuteChanged), _canExecuteChangedSubscriber);
+                    WeakEvents.CommandCanExecuteChanged.Unsubscribe(_command, _canExecuteChangedSubscriber);
 
                 SetAndRaise(CommandProperty, ref _command, value);
 
                 if (_command != null)
-                    WeakSubscriptionManager.Subscribe(_command,
-                        nameof(ICommand.CanExecuteChanged), _canExecuteChangedSubscriber);
+                    WeakEvents.CommandCanExecuteChanged.Subscribe(_command, _canExecuteChangedSubscriber);
 
                 CanExecuteChanged();
             }
diff --git a/src/Avalonia.Controls/Repeater/ItemsRepeater.cs b/src/Avalonia.Controls/Repeater/ItemsRepeater.cs
index ecc0fa3a48..b40cf26df5 100644
--- a/src/Avalonia.Controls/Repeater/ItemsRepeater.cs
+++ b/src/Avalonia.Controls/Repeater/ItemsRepeater.cs
@@ -20,7 +20,7 @@ namespace Avalonia.Controls
     /// Represents a data-driven collection control that incorporates a flexible layout system,
     /// custom views, and virtualization.
     /// </summary>
-    public class ItemsRepeater : Panel, IChildIndexProvider
+    public class ItemsRepeater : Panel, IChildIndexProvider, IWeakEventSubscriber<EventArgs>
     {
         /// <summary>
         /// Defines the <see cref="HorizontalCacheLength"/> property.
@@ -723,14 +723,8 @@ namespace Avalonia.Controls
             {
                 oldValue.UninitializeForContext(LayoutContext);
 
-                WeakEventHandlerManager.Unsubscribe<EventArgs, ItemsRepeater>(
-                    oldValue,
-                    nameof(AttachedLayout.MeasureInvalidated),
-                    InvalidateMeasureForLayout);
-                WeakEventHandlerManager.Unsubscribe<EventArgs, ItemsRepeater>(
-                    oldValue,
-                    nameof(AttachedLayout.ArrangeInvalidated),
-                    InvalidateArrangeForLayout);
+                AttachedLayout.MeasureInvalidatedWeakEvent.Unsubscribe(oldValue, this);
+                AttachedLayout.ArrangeInvalidatedWeakEvent.Unsubscribe(oldValue, this);
 
                 // Walk through all the elements and make sure they are cleared
                 foreach (var element in Children)
@@ -748,14 +742,8 @@ namespace Avalonia.Controls
             {
                 newValue.InitializeForContext(LayoutContext);
 
-                WeakEventHandlerManager.Subscribe<AttachedLayout, EventArgs, ItemsRepeater>(
-                    newValue,
-                    nameof(AttachedLayout.MeasureInvalidated),
-                    InvalidateMeasureForLayout);
-                WeakEventHandlerManager.Subscribe<AttachedLayout, EventArgs, ItemsRepeater>(
-                    newValue,
-                    nameof(AttachedLayout.ArrangeInvalidated),
-                    InvalidateArrangeForLayout);
+                AttachedLayout.MeasureInvalidatedWeakEvent.Subscribe(newValue, this);
+                AttachedLayout.ArrangeInvalidatedWeakEvent.Subscribe(newValue, this);
             }
 
             bool isVirtualizingLayout = newValue != null && newValue is VirtualizingLayout;
@@ -806,9 +794,13 @@ namespace Avalonia.Controls
             _viewportManager.OnBringIntoViewRequested(e);
         }
 
-        private void InvalidateMeasureForLayout(object sender, EventArgs e) => InvalidateMeasure();
-
-        private void InvalidateArrangeForLayout(object sender, EventArgs e) => InvalidateArrange();
+        void IWeakEventSubscriber<EventArgs>.OnEvent(object? sender, WeakEvent ev, EventArgs e)
+        {
+            if(ev == AttachedLayout.ArrangeInvalidatedWeakEvent)
+                InvalidateArrange();
+            else if (ev == AttachedLayout.MeasureInvalidatedWeakEvent)
+                InvalidateMeasure();
+        }
 
         private VirtualizingLayoutContext GetLayoutContext()
         {
diff --git a/src/Avalonia.Controls/TopLevel.cs b/src/Avalonia.Controls/TopLevel.cs
index 5d9a0c8eed..eaee5bdb50 100644
--- a/src/Avalonia.Controls/TopLevel.cs
+++ b/src/Avalonia.Controls/TopLevel.cs
@@ -34,7 +34,7 @@ namespace Avalonia.Controls
         IStyleHost,
         ILogicalRoot,
         ITextInputMethodRoot,
-        IWeakSubscriber<ResourcesChangedEventArgs>
+        IWeakEventSubscriber<ResourcesChangedEventArgs>
     {
         /// <summary>
         /// Defines the <see cref="ClientSize"/> property.
@@ -74,6 +74,12 @@ namespace Avalonia.Controls
         public static readonly StyledProperty<IBrush> TransparencyBackgroundFallbackProperty =
             AvaloniaProperty.Register<TopLevel, IBrush>(nameof(TransparencyBackgroundFallback), Brushes.White);
 
+        private static readonly WeakEvent<IResourceHost, ResourcesChangedEventArgs>
+            ResourcesChangedWeakEvent = WeakEvent.Register<IResourceHost, ResourcesChangedEventArgs>(
+                (s, h) => s.ResourcesChanged += h,
+                (s, h) => s.ResourcesChanged -= h
+            );
+
         private readonly IInputManager _inputManager;
         private readonly IAccessKeyHandler _accessKeyHandler;
         private readonly IKeyboardNavigationHandler _keyboardNavigationHandler;
@@ -178,10 +184,7 @@ namespace Avalonia.Controls
 
             if (((IStyleHost)this).StylingParent is IResourceHost applicationResources)
             {
-                WeakSubscriptionManager.Subscribe(
-                    applicationResources,
-                    nameof(IResourceHost.ResourcesChanged),
-                    this);
+                ResourcesChangedWeakEvent.Subscribe(applicationResources, this);
             }
 
             impl.LostFocus += PlatformImpl_LostFocus;
@@ -286,7 +289,7 @@ namespace Avalonia.Controls
         /// <inheritdoc/>
         IMouseDevice IInputRoot.MouseDevice => PlatformImpl?.MouseDevice;
 
-        void IWeakSubscriber<ResourcesChangedEventArgs>.OnEvent(object sender, ResourcesChangedEventArgs e)
+        void IWeakEventSubscriber<ResourcesChangedEventArgs>.OnEvent(object sender, WeakEvent ev, ResourcesChangedEventArgs e)
         {
             ((ILogical)this).NotifyResourcesChanged(e);
         }
diff --git a/src/Avalonia.Controls/Utils/CollectionChangedEventManager.cs b/src/Avalonia.Controls/Utils/CollectionChangedEventManager.cs
index 1a190391b7..74705a0262 100644
--- a/src/Avalonia.Controls/Utils/CollectionChangedEventManager.cs
+++ b/src/Avalonia.Controls/Utils/CollectionChangedEventManager.cs
@@ -83,7 +83,7 @@ namespace Avalonia.Controls.Utils
                 "Collection listener not registered for this collection/listener combination.");
         }
 
-        private class Entry : IWeakSubscriber<NotifyCollectionChangedEventArgs>, IDisposable
+        private class Entry : IWeakEventSubscriber<NotifyCollectionChangedEventArgs>, IDisposable
         {
             private INotifyCollectionChanged _collection;
 
@@ -91,23 +91,18 @@ namespace Avalonia.Controls.Utils
             {
                 _collection = collection;
                 Listeners = new List<WeakReference<ICollectionChangedListener>>();
-                WeakSubscriptionManager.Subscribe(
-                    _collection,
-                    nameof(INotifyCollectionChanged.CollectionChanged),
-                    this);
+                WeakEvents.CollectionChanged.Subscribe(_collection, this);
             }
 
             public List<WeakReference<ICollectionChangedListener>> Listeners { get; }
 
             public void Dispose()
             {
-                WeakSubscriptionManager.Unsubscribe(
-                    _collection,
-                    nameof(INotifyCollectionChanged.CollectionChanged),
-                    this);
+                WeakEvents.CollectionChanged.Unsubscribe(_collection, this);
             }
 
-            void IWeakSubscriber<NotifyCollectionChangedEventArgs>.OnEvent(object? sender, NotifyCollectionChangedEventArgs e)
+            void IWeakEventSubscriber<NotifyCollectionChangedEventArgs>.
+                OnEvent(object? notifyCollectionChanged, WeakEvent ev, NotifyCollectionChangedEventArgs e)
             {
                 static void Notify(
                     INotifyCollectionChanged incc,
diff --git a/src/Avalonia.Dialogs/AboutAvaloniaDialog.xaml b/src/Avalonia.Dialogs/AboutAvaloniaDialog.xaml
index 08e8798cd5..c959fdc143 100644
--- a/src/Avalonia.Dialogs/AboutAvaloniaDialog.xaml
+++ b/src/Avalonia.Dialogs/AboutAvaloniaDialog.xaml
@@ -95,7 +95,7 @@
       </StackPanel>
       <StackPanel Orientation="Horizontal" HorizontalAlignment="Center" >
         <TextBlock Text="Chat Room | " />
-        <Button Classes="Hyperlink" CommandParameter="https://gitter.im/AvaloniaUI/Avalonia/"  />
+        <Button Classes="Hyperlink" CommandParameter="https://t.me/Avalonia"  />
       </StackPanel>
      </StackPanel> 
     <StackPanel VerticalAlignment="Bottom" Margin="10">
diff --git a/src/Avalonia.Dialogs/ApiCompatBaseline.txt b/src/Avalonia.Dialogs/ApiCompatBaseline.txt
new file mode 100644
index 0000000000..9cb1b47015
--- /dev/null
+++ b/src/Avalonia.Dialogs/ApiCompatBaseline.txt
@@ -0,0 +1,3 @@
+Compat issues with assembly Avalonia.Dialogs:
+CannotRemoveBaseTypeOrInterface : Type 'Avalonia.Dialogs.AboutAvaloniaDialog' does not implement interface 'Avalonia.Utilities.IWeakSubscriber<Avalonia.Controls.ResourcesChangedEventArgs>' in the implementation but it does in the contract.
+Total Issues: 1
diff --git a/src/Avalonia.Dialogs/Avalonia.Dialogs.csproj b/src/Avalonia.Dialogs/Avalonia.Dialogs.csproj
index 475a3655e4..770d15ea27 100644
--- a/src/Avalonia.Dialogs/Avalonia.Dialogs.csproj
+++ b/src/Avalonia.Dialogs/Avalonia.Dialogs.csproj
@@ -5,6 +5,7 @@
 
   <ItemGroup>
     <AvaloniaResource Include="Assets\*" />
+    <AvaloniaResource Include="**/*.xaml" />
   </ItemGroup>
 
   <Import Project="..\..\build\BuildTargets.targets" />
diff --git a/src/Avalonia.Input/KeyBinding.cs b/src/Avalonia.Input/KeyBinding.cs
index 856157eafa..7cb4f443f3 100644
--- a/src/Avalonia.Input/KeyBinding.cs
+++ b/src/Avalonia.Input/KeyBinding.cs
@@ -35,9 +35,11 @@ namespace Avalonia.Input
         {
             if (Gesture?.Matches(args) == true)
             {
-                args.Handled = true;
-                if (Command?.CanExecute(CommandParameter) == true)
+                if (Command?.CanExecute(CommandParameter) == true) 
+                {
+                    args.Handled = true;
                     Command.Execute(CommandParameter);
+                }
             }
         }
     }
diff --git a/src/Avalonia.Layout/AttachedLayout.cs b/src/Avalonia.Layout/AttachedLayout.cs
index 6c884641f8..ece8bbe805 100644
--- a/src/Avalonia.Layout/AttachedLayout.cs
+++ b/src/Avalonia.Layout/AttachedLayout.cs
@@ -4,6 +4,7 @@
 // Licensed to The Avalonia Project under MIT License, courtesy of The .NET Foundation.
 
 using System;
+using Avalonia.Utilities;
 
 namespace Avalonia.Layout
 {
@@ -19,10 +20,26 @@ namespace Avalonia.Layout
         /// </summary>
         public event EventHandler? MeasureInvalidated;
 
+        /// <summary>
+        /// Occurs when the measurement state (layout) has been invalidated.
+        /// </summary>
+        public static readonly WeakEvent<AttachedLayout, EventArgs> MeasureInvalidatedWeakEvent =
+            WeakEvent.Register<AttachedLayout>(
+                (s, h) => s.MeasureInvalidated += h,
+                (s, h) => s.MeasureInvalidated -= h);
+
         /// <summary>
         /// Occurs when the arrange state (layout) has been invalidated.
         /// </summary>
         public event EventHandler? ArrangeInvalidated;
+        
+        /// <summary>
+        /// Occurs when the arrange state (layout) has been invalidated.
+        /// </summary>
+        public static readonly WeakEvent<AttachedLayout, EventArgs> ArrangeInvalidatedWeakEvent =
+            WeakEvent.Register<AttachedLayout>(
+                (s, h) => s.ArrangeInvalidated += h,
+                (s, h) => s.ArrangeInvalidated -= h);
 
         /// <summary>
         /// Initializes any per-container state the layout requires when it is attached to an
diff --git a/src/Avalonia.Native/AvaloniaNativeMenuExporter.cs b/src/Avalonia.Native/AvaloniaNativeMenuExporter.cs
index bda1c91750..de6ba30a85 100644
--- a/src/Avalonia.Native/AvaloniaNativeMenuExporter.cs
+++ b/src/Avalonia.Native/AvaloniaNativeMenuExporter.cs
@@ -70,81 +70,83 @@ namespace Avalonia.Native
             var result = new NativeMenu();
 
             var aboutItem = new NativeMenuItem("About Avalonia");
-            aboutItem.Click += async (sender, e) =>
+            
+            aboutItem.Click += async (_, _) =>
             {
                 var dialog = new AboutAvaloniaDialog();
 
-                var mainWindow = (Application.Current.ApplicationLifetime as IClassicDesktopStyleApplicationLifetime)?.MainWindow;
-
-                await dialog.ShowDialog(mainWindow);
+                if (Application.Current is
+                    { ApplicationLifetime: IClassicDesktopStyleApplicationLifetime { MainWindow: { } mainWindow } })
+                {
+                    await dialog.ShowDialog(mainWindow);   
+                }
             };
+            
             result.Add(aboutItem);
 
-            var macOpts = AvaloniaLocator.Current.GetService<MacOSPlatformOptions>();
-            if (macOpts == null || !macOpts.DisableDefaultApplicationMenuItems)
-            {
-                result.Add(new NativeMenuItemSeparator());
+            return result;
+        }
 
-                var servicesMenu = new NativeMenuItem("Services");
-                servicesMenu.Menu = new NativeMenu
-                {
-                    [MacOSNativeMenuCommands.IsServicesSubmenuProperty] = true
-                };
-                result.Add(servicesMenu);
+        private void PopulateStandardOSXMenuItems(NativeMenu appMenu)
+        {
+            appMenu.Add(new NativeMenuItemSeparator());
 
-                result.Add(new NativeMenuItemSeparator());
+            var servicesMenu = new NativeMenuItem("Services");
+            servicesMenu.Menu = new NativeMenu { [MacOSNativeMenuCommands.IsServicesSubmenuProperty] = true };
 
-                var hideItem = new NativeMenuItem("Hide " + Application.Current.Name)
-                {
-                    Gesture = new KeyGesture(Key.H, KeyModifiers.Meta)
-                };
-                hideItem.Click += (sender, args) =>
-                {
-                    _applicationCommands.HideApp();
-                };
-                result.Add(hideItem);
+            appMenu.Add(servicesMenu);
 
+            appMenu.Add(new NativeMenuItemSeparator());
 
-                var hideOthersItem = new NativeMenuItem("Hide Others")
-                {
-                    Gesture = new KeyGesture(Key.Q, KeyModifiers.Meta | KeyModifiers.Alt)
-                };
-                hideOthersItem.Click += (sender, args) =>
-                {
-                    _applicationCommands.HideOthers();
-                };
-                result.Add(hideOthersItem);
+            var hideItem = new NativeMenuItem("Hide " + (Application.Current?.Name ?? "Application"))
+            {
+                Gesture = new KeyGesture(Key.H, KeyModifiers.Meta)
+            };
 
+            hideItem.Click += (_, _) =>
+            {
+                _applicationCommands.HideApp();
+            };
 
-                var showAllItem = new NativeMenuItem("Show All");
-                showAllItem.Click += (sender, args) =>
-                {
-                    _applicationCommands.ShowAll();
-                };
-                result.Add(showAllItem);
+            appMenu.Add(hideItem);
 
-                result.Add(new NativeMenuItemSeparator());
+            var hideOthersItem = new NativeMenuItem("Hide Others")
+            {
+                Gesture = new KeyGesture(Key.Q, KeyModifiers.Meta | KeyModifiers.Alt)
+            };
+            hideOthersItem.Click += (_, _) =>
+            {
+                _applicationCommands.HideOthers();
+            };
+            appMenu.Add(hideOthersItem);
 
-                var quitItem = new NativeMenuItem("Quit")
-                {
-                    Gesture = new KeyGesture(Key.Q, KeyModifiers.Meta)
-                };
-                quitItem.Click += (sender, args) =>
-                {
-                    _applicationCommands.ShowAll();
-                };
-                result.Add(quitItem);
-            }
+            var showAllItem = new NativeMenuItem("Show All");
+            showAllItem.Click += (_, _) =>
+            {
+                _applicationCommands.ShowAll();
+            };
 
+            appMenu.Add(showAllItem);
 
-            return result;
+            appMenu.Add(new NativeMenuItemSeparator());
+
+            var quitItem = new NativeMenuItem("Quit") { Gesture = new KeyGesture(Key.Q, KeyModifiers.Meta) };
+            quitItem.Click += (_, _) =>
+            {
+                if (Application.Current is { ApplicationLifetime: IControlledApplicationLifetime lifetime })
+                {
+                    lifetime.Shutdown();
+                }
+            };
+
+            appMenu.Add(quitItem);
         }
 
         private void DoLayoutReset(bool forceUpdate = false)
         {
-            var macOpts = AvaloniaLocator.Current.GetService<MacOSPlatformOptions>();
+            var macOpts = AvaloniaLocator.Current.GetService<MacOSPlatformOptions>() ?? new MacOSPlatformOptions();
 
-            if (macOpts != null && macOpts.DisableNativeMenus)
+            if (macOpts.DisableNativeMenus)
             {
                 return;
             }
@@ -220,6 +222,13 @@ namespace Avalonia.Native
 
                 _nativeMenu.Initialize(this, appMenuHolder, "");
 
+                var macOpts = AvaloniaLocator.Current.GetService<MacOSPlatformOptions>();
+
+                if (macOpts == null || !macOpts.DisableDefaultApplicationMenuItems)
+                {
+                    PopulateStandardOSXMenuItems(menu);
+                }
+
                 setMenu = true;
             }
 
diff --git a/src/Avalonia.Native/AvaloniaNativePlatform.cs b/src/Avalonia.Native/AvaloniaNativePlatform.cs
index 5fa50f0e7f..1eadf70b13 100644
--- a/src/Avalonia.Native/AvaloniaNativePlatform.cs
+++ b/src/Avalonia.Native/AvaloniaNativePlatform.cs
@@ -96,9 +96,9 @@ namespace Avalonia.Native
             _factory.Initialize(new GCHandleDeallocator(), applicationPlatform);
             if (_factory.MacOptions != null)
             {
-                var macOpts = AvaloniaLocator.Current.GetService<MacOSPlatformOptions>();
+                var macOpts = AvaloniaLocator.Current.GetService<MacOSPlatformOptions>() ?? new MacOSPlatformOptions();
 
-                _factory.MacOptions.SetShowInDock(macOpts?.ShowInDock != false ? 1 : 0);
+                _factory.MacOptions.SetShowInDock(macOpts.ShowInDock ? 1 : 0);
             }
 
             AvaloniaLocator.CurrentMutable
diff --git a/src/Avalonia.Native/WindowImplBase.cs b/src/Avalonia.Native/WindowImplBase.cs
index 4a3baa2788..87b7a7608e 100644
--- a/src/Avalonia.Native/WindowImplBase.cs
+++ b/src/Avalonia.Native/WindowImplBase.cs
@@ -28,18 +28,18 @@ namespace Avalonia.Native
 
         public string HandleDescriptor => "NSWindow";
 
-        public IntPtr NSView => _native.ObtainNSViewHandle();
+        public IntPtr NSView => _native?.ObtainNSViewHandle() ?? IntPtr.Zero;
 
-        public IntPtr NSWindow => _native.ObtainNSWindowHandle();
+        public IntPtr NSWindow => _native?.ObtainNSWindowHandle() ?? IntPtr.Zero;
 
         public IntPtr GetNSViewRetained()
         {
-            return _native.ObtainNSViewHandleRetained();
+            return _native?.ObtainNSViewHandleRetained() ?? IntPtr.Zero;
         }
 
         public IntPtr GetNSWindowRetained()
         {
-            return _native.ObtainNSWindowHandleRetained();
+            return _native?.ObtainNSWindowHandleRetained() ?? IntPtr.Zero;
         }
     }
 
@@ -260,7 +260,7 @@ namespace Avalonia.Native
 
         public void Activate()
         {
-            _native.Activate();
+            _native?.Activate();
         }
 
         public bool RawTextInputEvent(uint timeStamp, string text)
@@ -322,7 +322,7 @@ namespace Avalonia.Native
 
         public void Resize(Size clientSize, PlatformResizeReason reason)
         {
-            _native.Resize(clientSize.Width, clientSize.Height, (AvnPlatformResizeReason)reason);
+            _native?.Resize(clientSize.Width, clientSize.Height, (AvnPlatformResizeReason)reason);
         }
 
         public IRenderer CreateRenderer(IRenderRoot root)
@@ -367,14 +367,14 @@ namespace Avalonia.Native
 
         public virtual void Show(bool activate, bool isDialog)
         {
-            _native.Show(activate.AsComBool(), isDialog.AsComBool());
+            _native?.Show(activate.AsComBool(), isDialog.AsComBool());
         }
 
 
         public PixelPoint Position
         {
-            get => _native.Position.ToAvaloniaPixelPoint();
-            set => _native.SetPosition(value.ToAvnPoint());
+            get => _native?.Position.ToAvaloniaPixelPoint() ?? default;
+            set => _native?.SetPosition(value.ToAvnPoint());
         }
 
         public Point PointToClient(PixelPoint point)
@@ -389,12 +389,12 @@ namespace Avalonia.Native
 
         public void Hide()
         {
-            _native.Hide();
+            _native?.Hide();
         }
 
         public void BeginMoveDrag(PointerPressedEventArgs e)
         {
-            _native.BeginMoveDrag();
+            _native?.BeginMoveDrag();
         }
 
         public Size MaxAutoSizeHint => Screen.AllScreens.Select(s => s.Bounds.Size.ToSize(1))
@@ -402,7 +402,7 @@ namespace Avalonia.Native
 
         public void SetTopmost(bool value)
         {
-            _native.SetTopMost(value.AsComBool());
+            _native?.SetTopMost(value.AsComBool());
         }
 
         public double RenderScaling => _native?.Scaling ?? 1;
@@ -438,7 +438,7 @@ namespace Avalonia.Native
 
         public void SetMinMaxSize(Size minSize, Size maxSize)
         {
-            _native.SetMinMaxSize(minSize.ToAvnSize(), maxSize.ToAvnSize());
+            _native?.SetMinMaxSize(minSize.ToAvnSize(), maxSize.ToAvnSize());
         }
 
         public void BeginResizeDrag(WindowEdge edge, PointerPressedEventArgs e)
@@ -449,7 +449,7 @@ namespace Avalonia.Native
         internal void BeginDraggingSession(AvnDragDropEffects effects, AvnPoint point, IAvnClipboard clipboard,
             IAvnDndResultCallback callback, IntPtr sourceHandle)
         {
-            _native.BeginDragAndDropOperation(effects, point, clipboard, callback, sourceHandle);
+            _native?.BeginDragAndDropOperation(effects, point, clipboard, callback, sourceHandle);
         }
 
         public void SetTransparencyLevelHint(WindowTransparencyLevel transparencyLevel) 
diff --git a/src/Avalonia.Themes.Fluent/Controls/CalendarDatePicker.xaml b/src/Avalonia.Themes.Fluent/Controls/CalendarDatePicker.xaml
index 6c4e94caf1..26c3bbc19f 100644
--- a/src/Avalonia.Themes.Fluent/Controls/CalendarDatePicker.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/CalendarDatePicker.xaml
@@ -33,6 +33,7 @@
     
     <Setter Property="Template">
       <ControlTemplate>
+        <DataValidationErrors>
         <Grid ColumnDefinitions="*,Auto">
 
           <Grid.Styles>
@@ -107,7 +108,6 @@
                    Padding="{TemplateBinding Padding}"
                    Watermark="{TemplateBinding Watermark}"
                    UseFloatingWatermark="{TemplateBinding UseFloatingWatermark}"
-                   DataValidationErrors.Errors="{TemplateBinding (DataValidationErrors.Errors)}"
                    VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"
                    HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"
                    Grid.Column="0"/>
@@ -136,8 +136,12 @@
                       DisplayDateEnd="{TemplateBinding DisplayDateEnd}" />
           </Popup>
         </Grid>
+        </DataValidationErrors>
       </ControlTemplate>
     </Setter>
   </Style>
   
+  <Style Selector="CalendarDatePicker:error TextBox /template/ Border#PART_BorderElement">
+    <Setter Property="BorderBrush" Value="{DynamicResource SystemControlErrorTextForegroundBrush}"/>
+  </Style>
 </Styles>
diff --git a/src/Avalonia.Themes.Fluent/Controls/ListBox.xaml b/src/Avalonia.Themes.Fluent/Controls/ListBox.xaml
index 47704c12bd..1b4d66405b 100644
--- a/src/Avalonia.Themes.Fluent/Controls/ListBox.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/ListBox.xaml
@@ -20,6 +20,7 @@
     <Setter Property="Template">
       <ControlTemplate>
         <Border Name="border"
+                ClipToBounds="{TemplateBinding ClipToBounds}"
                 Background="{TemplateBinding Background}"
                 BorderBrush="{TemplateBinding BorderBrush}"
                 BorderThickness="{TemplateBinding BorderThickness}"
diff --git a/src/Avalonia.Visuals/Animation/Animators/BaseBrushAnimator.cs b/src/Avalonia.Visuals/Animation/Animators/BaseBrushAnimator.cs
index a2c4b0313b..5f22254fb5 100644
--- a/src/Avalonia.Visuals/Animation/Animators/BaseBrushAnimator.cs
+++ b/src/Avalonia.Visuals/Animation/Animators/BaseBrushAnimator.cs
@@ -38,8 +38,8 @@ namespace Avalonia.Animation.Animators
         }
 
         /// <inheritdoc/>
-        public override IDisposable Apply(Animation animation, Animatable control, IClock clock,
-            IObservable<bool> match, Action onComplete)
+        public override IDisposable? Apply(Animation animation, Animatable control, IClock? clock,
+            IObservable<bool> match, Action? onComplete)
         {
             if (TryCreateCustomRegisteredAnimator(out var animator)
                 || TryCreateGradientAnimator(out animator)
@@ -135,9 +135,8 @@ namespace Avalonia.Animation.Animators
 
         private bool TryCreateCustomRegisteredAnimator([NotNullWhen(true)] out IAnimator? animator)
         {
-            if (_brushAnimators.Count > 0)
+            if (_brushAnimators.Count > 0 && this[0].Value?.GetType() is Type firstKeyType)
             {
-                var firstKeyType = this[0].Value.GetType();
                 foreach (var (match, animatorType) in _brushAnimators)
                 {
                     if (!match(firstKeyType))
diff --git a/src/Avalonia.Visuals/Animation/Animators/GradientBrushAnimator.cs b/src/Avalonia.Visuals/Animation/Animators/GradientBrushAnimator.cs
index 864e12413f..0979de16d0 100644
--- a/src/Avalonia.Visuals/Animation/Animators/GradientBrushAnimator.cs
+++ b/src/Avalonia.Visuals/Animation/Animators/GradientBrushAnimator.cs
@@ -58,6 +58,11 @@ namespace Avalonia.Animation.Animators
 
         public override IDisposable BindAnimation(Animatable control, IObservable<IGradientBrush?> instance)
         {
+            if (Property is null)
+            {
+                throw new InvalidOperationException("Animator has no property specified.");
+            }
+
             return control.Bind((AvaloniaProperty<IBrush?>)Property, instance, BindingPriority.Animation);
         }
 
diff --git a/src/Avalonia.Visuals/Animation/Animators/SolidColorBrushAnimator.cs b/src/Avalonia.Visuals/Animation/Animators/SolidColorBrushAnimator.cs
index 7c6372aae2..57f9f3c1a5 100644
--- a/src/Avalonia.Visuals/Animation/Animators/SolidColorBrushAnimator.cs
+++ b/src/Avalonia.Visuals/Animation/Animators/SolidColorBrushAnimator.cs
@@ -24,6 +24,11 @@ namespace Avalonia.Animation.Animators
 
         public override IDisposable BindAnimation(Animatable control, IObservable<ISolidColorBrush?> instance)
         {
+            if (Property is null)
+            {
+                throw new InvalidOperationException("Animator has no property specified.");
+            }
+
             return control.Bind((AvaloniaProperty<IBrush?>)Property, instance, BindingPriority.Animation);
         }
     }
diff --git a/src/Avalonia.Visuals/Animation/Animators/TransformAnimator.cs b/src/Avalonia.Visuals/Animation/Animators/TransformAnimator.cs
index 1d7bfd3748..34ec8ac503 100644
--- a/src/Avalonia.Visuals/Animation/Animators/TransformAnimator.cs
+++ b/src/Avalonia.Visuals/Animation/Animators/TransformAnimator.cs
@@ -14,10 +14,15 @@ namespace Avalonia.Animation.Animators
         DoubleAnimator? _doubleAnimator;
 
         /// <inheritdoc/>
-        public override IDisposable? Apply(Animation animation, Animatable control, IClock clock, IObservable<bool> obsMatch, Action onComplete)
+        public override IDisposable? Apply(Animation animation, Animatable control, IClock? clock, IObservable<bool> obsMatch, Action? onComplete)
         {
             var ctrl = (Visual)control;
 
+            if (Property is null)
+            {
+                throw new InvalidOperationException("Animator has no property specified.");
+            }
+
             // Check if the Target Property is Transform derived.
             if (typeof(Transform).IsAssignableFrom(Property.OwnerType))
             {
diff --git a/src/Avalonia.Visuals/ApiCompatBaseline.txt b/src/Avalonia.Visuals/ApiCompatBaseline.txt
index dcb3246a63..68e3673cfe 100644
--- a/src/Avalonia.Visuals/ApiCompatBaseline.txt
+++ b/src/Avalonia.Visuals/ApiCompatBaseline.txt
@@ -7,6 +7,9 @@ InterfacesShouldHaveSameMembers : Interface member 'public System.Threading.Task
 MembersMustExist : Member 'public System.Threading.Tasks.Task Avalonia.Animation.PageSlide.Start(Avalonia.Visual, Avalonia.Visual, System.Boolean)' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public void Avalonia.Media.GlyphRun..ctor()' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public void Avalonia.Media.GlyphRun.GlyphTypeface.set(Avalonia.Media.GlyphTypeface)' does not exist in the implementation but it does exist in the contract.
+CannotSealType : Type 'Avalonia.Media.Pen' is actually (has the sealed modifier) sealed in the implementation but not sealed in the contract.
+MembersMustExist : Member 'protected void Avalonia.Media.Pen.AffectsRender<T>(Avalonia.AvaloniaProperty[])' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'protected void Avalonia.Media.Pen.RaiseInvalidated(System.EventArgs)' does not exist in the implementation but it does exist in the contract.
 TypeCannotChangeClassification : Type 'Avalonia.Media.Immutable.ImmutableSolidColorBrush' is a 'class' in the implementation but is a 'struct' in the contract.
 MembersMustExist : Member 'public void Avalonia.Media.TextFormatting.DrawableTextRun.Draw(Avalonia.Media.DrawingContext)' does not exist in the implementation but it does exist in the contract.
 CannotAddAbstractMembers : Member 'public void Avalonia.Media.TextFormatting.DrawableTextRun.Draw(Avalonia.Media.DrawingContext, Avalonia.Point)' is abstract in the implementation but is missing in the contract.
@@ -83,4 +86,4 @@ InterfacesShouldHaveSameMembers : Interface member 'public Avalonia.Size Avaloni
 InterfacesShouldHaveSameMembers : Interface member 'public System.TimeSpan Avalonia.Platform.IPlatformSettings.TouchDoubleClickTime' is present in the implementation but not in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public Avalonia.Size Avalonia.Platform.IPlatformSettings.TouchDoubleClickSize.get()' is present in the implementation but not in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public System.TimeSpan Avalonia.Platform.IPlatformSettings.TouchDoubleClickTime.get()' is present in the implementation but not in the contract.
-Total Issues: 84
+Total Issues: 87
diff --git a/src/Avalonia.Visuals/Media/Pen.cs b/src/Avalonia.Visuals/Media/Pen.cs
index 7c966a35cf..65ba851100 100644
--- a/src/Avalonia.Visuals/Media/Pen.cs
+++ b/src/Avalonia.Visuals/Media/Pen.cs
@@ -7,7 +7,7 @@ namespace Avalonia.Media
     /// <summary>
     /// Describes how a stroke is drawn.
     /// </summary>
-    public class Pen : AvaloniaObject, IPen
+    public sealed class Pen : AvaloniaObject, IPen, IWeakEventSubscriber<EventArgs>
     {
         /// <summary>
         /// Defines the <see cref="Brush"/> property.
@@ -45,6 +45,10 @@ namespace Avalonia.Media
         public static readonly StyledProperty<double> MiterLimitProperty =
             AvaloniaProperty.Register<Pen, double>(nameof(MiterLimit), 10.0);
 
+        private EventHandler? _invalidated;
+        private IAffectsRender? _subscribedToBrush;
+        private IAffectsRender? _subscribedToDashes;
+        
         /// <summary>
         /// Initializes a new instance of the <see cref="Pen"/> class.
         /// </summary>
@@ -96,17 +100,6 @@ namespace Avalonia.Media
             DashStyle = dashStyle;
         }
 
-        static Pen()
-        {
-            AffectsRender<Pen>(
-                BrushProperty,
-                ThicknessProperty,
-                DashStyleProperty,
-                LineCapProperty,
-                LineJoinProperty,
-                MiterLimitProperty);
-        }
-
         /// <summary>
         /// Gets or sets the brush used to draw the stroke.
         /// </summary>
@@ -116,6 +109,11 @@ namespace Avalonia.Media
             set => SetValue(BrushProperty, value);
         }
 
+        private static readonly WeakEvent<IAffectsRender, EventArgs> InvalidatedWeakEvent =
+            WeakEvent.Register<IAffectsRender>(
+                (s, h) => s.Invalidated += h,
+                (s, h) => s.Invalidated -= h);
+
         /// <summary>
         /// Gets or sets the stroke thickness.
         /// </summary>
@@ -165,7 +163,19 @@ namespace Avalonia.Media
         /// <summary>
         /// Raised when the pen changes.
         /// </summary>
-        public event EventHandler? Invalidated;
+        public event EventHandler? Invalidated
+        {
+            add
+            {
+                _invalidated += value;
+                UpdateSubscriptions();
+            }
+            remove
+            {
+                _invalidated -= value; 
+                UpdateSubscriptions();
+            }
+        }
 
         /// <summary>
         /// Creates an immutable clone of the brush.
@@ -182,68 +192,42 @@ namespace Avalonia.Media
                 MiterLimit);
         }
 
-        /// <summary>
-        /// Marks a property as affecting the pen's visual representation.
-        /// </summary>
-        /// <param name="properties">The properties.</param>
-        /// <remarks>
-        /// After a call to this method in a pen's static constructor, any change to the
-        /// property will cause the <see cref="Invalidated"/> event to be raised on the pen.
-        /// </remarks>
-        protected static void AffectsRender<T>(params AvaloniaProperty[] properties)
-            where T : Pen
+        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
         {
-            static void Invalidate(AvaloniaPropertyChangedEventArgs e)
-            {
-                if (e.Sender is T sender)
-                {
-                    sender.RaiseInvalidated(EventArgs.Empty);
-                }
-            }
+            _invalidated?.Invoke(this, EventArgs.Empty);
+            if(change.Property == BrushProperty)
+                UpdateSubscription(ref _subscribedToBrush, Brush);
+            if(change.Property == DashStyleProperty)
+                UpdateSubscription(ref _subscribedToDashes, DashStyle);
+            base.OnPropertyChanged(change);
+        }
 
-            static void InvalidateAndSubscribe(AvaloniaPropertyChangedEventArgs e)
+        
+        void UpdateSubscription(ref IAffectsRender? field, object? value)
+        {
+            if ((_invalidated == null || field != value) && field != null)
             {
-                if (e.Sender is T sender)
-                {
-                    if (e.OldValue is IAffectsRender oldValue)
-                    {
-                        WeakEventHandlerManager.Unsubscribe<EventArgs, T>(
-                            oldValue,
-                            nameof(oldValue.Invalidated),
-                            sender.AffectsRenderInvalidated);
-                    }
-
-                    if (e.NewValue is IAffectsRender newValue)
-                    {
-                        WeakEventHandlerManager.Subscribe<IAffectsRender, EventArgs, T>(
-                            newValue,
-                            nameof(newValue.Invalidated),
-                            sender.AffectsRenderInvalidated);
-                    }
-
-                    sender.RaiseInvalidated(EventArgs.Empty);
-                }
+                InvalidatedWeakEvent.Unsubscribe(field, this);
+                field = null;
             }
 
-            foreach (var property in properties)
+            if (_invalidated != null && field != value && value is IAffectsRender affectsRender)
             {
-                if (property.CanValueAffectRender())
-                {
-                    property.Changed.Subscribe(e => InvalidateAndSubscribe(e));
-                }
-                else
-                {
-                    property.Changed.Subscribe(e => Invalidate(e));
-                }
+                InvalidatedWeakEvent.Subscribe(affectsRender, this);
+                field = affectsRender;
             }
         }
 
-        /// <summary>
-        /// Raises the <see cref="Invalidated"/> event.
-        /// </summary>
-        /// <param name="e">The event args.</param>
-        protected void RaiseInvalidated(EventArgs e) => Invalidated?.Invoke(this, e);
-
-        private void AffectsRenderInvalidated(object? sender, EventArgs e) => RaiseInvalidated(EventArgs.Empty);
+        void UpdateSubscriptions()
+        {
+            UpdateSubscription(ref _subscribedToBrush, Brush);
+            UpdateSubscription(ref _subscribedToDashes, DashStyle);
+        }
+        
+        void IWeakEventSubscriber<EventArgs>.OnEvent(object? sender, WeakEvent ev, EventArgs e)
+        {
+            if (ev == InvalidatedWeakEvent) 
+                _invalidated?.Invoke(this, EventArgs.Empty);
+        }
     }
 }
diff --git a/src/Avalonia.Visuals/Rendering/SceneGraph/SceneBuilder.cs b/src/Avalonia.Visuals/Rendering/SceneGraph/SceneBuilder.cs
index cb916293ac..63c22efc3f 100644
--- a/src/Avalonia.Visuals/Rendering/SceneGraph/SceneBuilder.cs
+++ b/src/Avalonia.Visuals/Rendering/SceneGraph/SceneBuilder.cs
@@ -126,7 +126,12 @@ namespace Avalonia.Rendering.SceneGraph
 
             while (node == null && visual.IsVisible)
             {
-                visual = visual.VisualParent!;
+                var parent = visual.VisualParent;
+
+                if (parent is null)
+                    return null;
+
+                visual = parent;
                 node = scene.FindNode(visual);
             }
 
diff --git a/src/Avalonia.X11/Glx/GlxDisplay.cs b/src/Avalonia.X11/Glx/GlxDisplay.cs
index fa8c866c09..fcdc10e999 100644
--- a/src/Avalonia.X11/Glx/GlxDisplay.cs
+++ b/src/Avalonia.X11/Glx/GlxDisplay.cs
@@ -95,8 +95,8 @@ namespace Avalonia.X11.Glx
 
                 if (Environment.GetEnvironmentVariable("AVALONIA_GLX_IGNORE_RENDERER_BLACKLIST") != "1")
                 {
-                    var blacklist = AvaloniaLocator.Current.GetService<X11PlatformOptions>()
-                        ?.GlxRendererBlacklist;
+                    var opts = AvaloniaLocator.Current.GetService<X11PlatformOptions>() ?? new X11PlatformOptions();
+                    var blacklist = opts.GlxRendererBlacklist;
                     if (blacklist != null)
                         foreach (var item in blacklist)
                             if (glInterface.Renderer.Contains(item))
diff --git a/src/Linux/Avalonia.LinuxFramebuffer/LinuxFramebufferPlatform.cs b/src/Linux/Avalonia.LinuxFramebuffer/LinuxFramebufferPlatform.cs
index f4db6bf48a..4add4c423b 100644
--- a/src/Linux/Avalonia.LinuxFramebuffer/LinuxFramebufferPlatform.cs
+++ b/src/Linux/Avalonia.LinuxFramebuffer/LinuxFramebufferPlatform.cs
@@ -38,11 +38,11 @@ namespace Avalonia.LinuxFramebuffer
             if (_fb is IGlOutputBackend gl)
                 AvaloniaLocator.CurrentMutable.Bind<IPlatformOpenGlInterface>().ToConstant(gl.PlatformOpenGlInterface);
             
-            var opts = AvaloniaLocator.Current.GetService<LinuxFramebufferPlatformOptions>();
+            var opts = AvaloniaLocator.Current.GetService<LinuxFramebufferPlatformOptions>() ?? new LinuxFramebufferPlatformOptions();
             
             AvaloniaLocator.CurrentMutable
                 .Bind<IPlatformThreadingInterface>().ToConstant(Threading)
-                .Bind<IRenderTimer>().ToConstant(new DefaultRenderTimer(opts?.Fps ?? 60))
+                .Bind<IRenderTimer>().ToConstant(new DefaultRenderTimer(opts.Fps))
                 .Bind<IRenderLoop>().ToConstant(new RenderLoop())
                 .Bind<ICursorFactory>().ToTransient<CursorFactoryStub>()
                 .Bind<IKeyboardDevice>().ToConstant(new KeyboardDevice())
diff --git a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/PropertyInfoAccessorFactory.cs b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/PropertyInfoAccessorFactory.cs
index b3f78bfbe3..c21a2d4299 100644
--- a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/PropertyInfoAccessorFactory.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/PropertyInfoAccessorFactory.cs
@@ -72,7 +72,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
         }
     }
 
-    internal class InpcPropertyAccessor : PropertyAccessorBase
+    internal class InpcPropertyAccessor : PropertyAccessorBase, IWeakEventSubscriber<PropertyChangedEventArgs>
     {
         protected readonly WeakReference<object> _reference;
         private readonly IPropertyInfo _property;
@@ -110,7 +110,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
             return false;
         }
 
-        void OnNotifyPropertyChanged(object sender, PropertyChangedEventArgs e)
+        public void OnEvent(object sender, WeakEvent ev, PropertyChangedEventArgs e)
         {
             if (e.PropertyName == _property.Name || string.IsNullOrEmpty(e.PropertyName))
             {
@@ -128,10 +128,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
         {
             if (_reference.TryGetTarget(out var o) && o is INotifyPropertyChanged inpc)
             {
-                WeakEventHandlerManager.Unsubscribe<PropertyChangedEventArgs, InpcPropertyAccessor>(
-                    inpc,
-                    nameof(INotifyPropertyChanged.PropertyChanged),
-                    OnNotifyPropertyChanged);
+                WeakEvents.PropertyChanged.Unsubscribe(inpc, this);
             }
         }
 
@@ -148,16 +145,11 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
         private void SubscribeToChanges()
         {
             if (_reference.TryGetTarget(out var o) && o is INotifyPropertyChanged inpc)
-            {
-                WeakEventHandlerManager.Subscribe<INotifyPropertyChanged, PropertyChangedEventArgs, InpcPropertyAccessor>(
-                    inpc,
-                    nameof(INotifyPropertyChanged.PropertyChanged),
-                    OnNotifyPropertyChanged);
-            }
+                WeakEvents.PropertyChanged.Subscribe(inpc, this);
         }
     }
 
-    internal class IndexerAccessor : InpcPropertyAccessor
+    internal class IndexerAccessor : InpcPropertyAccessor, IWeakEventSubscriber<NotifyCollectionChangedEventArgs>
     {
         private int _index;
 
@@ -172,27 +164,17 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
         {
             base.SubscribeCore();
             if (_reference.TryGetTarget(out var o) && o is INotifyCollectionChanged incc)
-            {
-                WeakEventHandlerManager.Subscribe<INotifyCollectionChanged, NotifyCollectionChangedEventArgs, IndexerAccessor>(
-                  incc,
-                  nameof(INotifyCollectionChanged.CollectionChanged),
-                  OnNotifyCollectionChanged);
-            }
+                WeakEvents.CollectionChanged.Subscribe(incc, this);
         }
 
         protected override void UnsubscribeCore()
         {
             base.UnsubscribeCore();
             if (_reference.TryGetTarget(out var o) && o is INotifyCollectionChanged incc)
-            {
-                WeakEventHandlerManager.Unsubscribe<NotifyCollectionChangedEventArgs, IndexerAccessor>(
-                  incc,
-                  nameof(INotifyCollectionChanged.CollectionChanged),
-                  OnNotifyCollectionChanged);
-            }
+                WeakEvents.CollectionChanged.Unsubscribe(incc, this);
         }
-
-        void OnNotifyCollectionChanged(object sender, NotifyCollectionChangedEventArgs args)
+        
+        public void OnEvent(object? sender, WeakEvent ev, NotifyCollectionChangedEventArgs args)
         {
             if (ShouldNotifyListeners(args))
             {
diff --git a/src/Web/Avalonia.Web.Blazor/AvaloniaView.razor.cs b/src/Web/Avalonia.Web.Blazor/AvaloniaView.razor.cs
index 4b0ada1f27..7644514687 100644
--- a/src/Web/Avalonia.Web.Blazor/AvaloniaView.razor.cs
+++ b/src/Web/Avalonia.Web.Blazor/AvaloniaView.razor.cs
@@ -259,7 +259,11 @@ namespace Avalonia.Web.Blazor
 
                     _inputHelper.Hide();
                     _canvasHelper.SetCursor("default");
-                    _topLevelImpl.SetCssCursor = _canvasHelper.SetCursor;
+                    _topLevelImpl.SetCssCursor = x =>
+                    {
+                        _inputHelper.SetCursor(x);//macOS
+                        _canvasHelper.SetCursor(x);//windows
+                    };
 
                     Console.WriteLine("starting html canvas setup");
                     _interop = await SKHtmlCanvasInterop.ImportAsync(Js, _htmlCanvas, OnRenderFrame);
diff --git a/src/Web/Avalonia.Web.Blazor/RazorViewTopLevelImpl.cs b/src/Web/Avalonia.Web.Blazor/RazorViewTopLevelImpl.cs
index ac5f5044d8..1d667c0f0c 100644
--- a/src/Web/Avalonia.Web.Blazor/RazorViewTopLevelImpl.cs
+++ b/src/Web/Avalonia.Web.Blazor/RazorViewTopLevelImpl.cs
@@ -127,15 +127,11 @@ namespace Avalonia.Web.Blazor
 
         public void SetCursor(ICursorImpl cursor)
         {
-            var cur = cursor as CssCursor;
-            var val = CssCursor.Default;
-            if (cur != null && cur.Value != null)
-            {
-                val = cur.Value;
-            }
+            var val = (cursor as CssCursor)?.Value ?? CssCursor.Default;
             if (_currentCursor != val)
             {
                 SetCssCursor?.Invoke(val);
+                _currentCursor = val;
             }
         }
 
diff --git a/src/Windows/Avalonia.Win32/Win32GlManager.cs b/src/Windows/Avalonia.Win32/Win32GlManager.cs
index 289c100d51..0376a41f8c 100644
--- a/src/Windows/Avalonia.Win32/Win32GlManager.cs
+++ b/src/Windows/Avalonia.Win32/Win32GlManager.cs
@@ -13,19 +13,18 @@ namespace Avalonia.Win32
         {
             AvaloniaLocator.CurrentMutable.Bind<IPlatformOpenGlInterface>().ToLazy<IPlatformOpenGlInterface>(() =>
             {
-                var opts = AvaloniaLocator.Current.GetService<Win32PlatformOptions>();
-                if (opts?.UseWgl == true)
+                var opts = AvaloniaLocator.Current.GetService<Win32PlatformOptions>() ?? new Win32PlatformOptions();
+                if (opts.UseWgl)
                 {
                     var wgl = WglPlatformOpenGlInterface.TryCreate();
                     return wgl;
                 }
 
-                if (opts?.AllowEglInitialization ?? Win32Platform.WindowsVersion > PlatformConstants.Windows7)
+                if (opts.AllowEglInitialization ?? Win32Platform.WindowsVersion > PlatformConstants.Windows7)
                 {
                     var egl = EglPlatformOpenGlInterface.TryCreate(() => new AngleWin32EglDisplay());
 
-                    if (egl != null &&
-                        opts?.UseWindowsUIComposition == true)
+                    if (egl != null && opts.UseWindowsUIComposition)
                     {
                         WinUICompositorConnection.TryCreateAndRegister(egl, opts.CompositionBackdropCornerRadius);
                     }
diff --git a/tests/Avalonia.Animation.UnitTests/AnimatableTests.cs b/tests/Avalonia.Animation.UnitTests/AnimatableTests.cs
index 26d8059eec..1d5296bebd 100644
--- a/tests/Avalonia.Animation.UnitTests/AnimatableTests.cs
+++ b/tests/Avalonia.Animation.UnitTests/AnimatableTests.cs
@@ -36,7 +36,7 @@ namespace Avalonia.Animation.UnitTests
         [Fact]
         public void Transition_Is_Not_Applied_To_Initial_Style()
         {
-            using (UnitTestApplication.Start(TestServices.RealStyler))
+            using (Start())
             {
                 var target = CreateTarget();
                 var control = new Control
@@ -74,6 +74,7 @@ namespace Avalonia.Animation.UnitTests
         [Fact]
         public void Transition_Is_Applied_When_Local_Value_Changes()
         {
+            using var app = Start();
             var target = CreateTarget();
             var control = CreateControl(target.Object);
 
@@ -170,6 +171,7 @@ namespace Avalonia.Animation.UnitTests
         [Fact]
         public void Transition_Is_Not_Applied_When_StyleTrigger_Changes_With_LocalValue_Present()
         {
+            using var app = Start();
             var target = CreateTarget();
             var control = CreateControl(target.Object);
 
@@ -195,6 +197,7 @@ namespace Avalonia.Animation.UnitTests
         [Fact]
         public void Transition_Is_Disposed_When_Local_Value_Changes()
         {
+            using var app = Start();
             var target = CreateTarget();
             var control = CreateControl(target.Object);
             var sub = new Mock<IDisposable>();
@@ -211,6 +214,7 @@ namespace Avalonia.Animation.UnitTests
         [Fact]
         public void New_Transition_Is_Applied_When_Local_Value_Changes()
         {
+            using var app = Start();
             var target = CreateTarget();
             var control = CreateControl(target.Object);
 
@@ -239,6 +243,7 @@ namespace Avalonia.Animation.UnitTests
         [Fact]
         public void Transition_Is_Not_Applied_When_Removed_From_Visual_Tree()
         {
+            using var app = Start();
             var target = CreateTarget();
             var control = CreateControl(target.Object);
 
@@ -266,6 +271,7 @@ namespace Avalonia.Animation.UnitTests
         [Fact]
         public void Animation_Is_Cancelled_When_Transition_Removed()
         {
+            using var app = Start();
             var target = CreateTarget();
             var control = CreateControl(target.Object);
             var sub = new Mock<IDisposable>();
@@ -285,7 +291,7 @@ namespace Avalonia.Animation.UnitTests
         [Fact]
         public void Animation_Is_Cancelled_When_New_Style_Activates()
         {
-            using (UnitTestApplication.Start(TestServices.RealStyler))
+            using (Start())
             {
                 var target = CreateTarget();
                 var control = CreateStyledControl(target.Object);
@@ -301,7 +307,7 @@ namespace Avalonia.Animation.UnitTests
 
                 target.Verify(x => x.Apply(
                     control,
-                    It.IsAny<Clock>(),
+                    It.IsAny<IClock>(),
                     1.0,
                     0.5),
                     Times.Once);
@@ -315,7 +321,7 @@ namespace Avalonia.Animation.UnitTests
         [Fact]
         public void Transition_From_Style_Trigger_Is_Applied()
         {
-            using (UnitTestApplication.Start(TestServices.RealStyler))
+            using (Start())
             {
                 var target = CreateTransition(Control.WidthProperty);
                 var control = CreateStyledControl(transition2: target.Object);
@@ -326,7 +332,7 @@ namespace Avalonia.Animation.UnitTests
 
                 target.Verify(x => x.Apply(
                     control,
-                    It.IsAny<Clock>(),
+                    It.IsAny<IClock>(),
                     double.NaN,
                     100.0),
                     Times.Once);
@@ -337,7 +343,7 @@ namespace Avalonia.Animation.UnitTests
         public void Replacing_Transitions_During_Animation_Does_Not_Throw_KeyNotFound()
         {
             // Issue #4059
-            using (UnitTestApplication.Start(TestServices.RealStyler))
+            using (Start())
             {
                 Border target;
                 var clock = new TestClock();
@@ -428,6 +434,13 @@ namespace Avalonia.Animation.UnitTests
             control.EndBatchUpdate();
         }
 
+        private static IDisposable Start()
+        {
+            var clock = new MockGlobalClock();
+            var services = TestServices.RealStyler.With(globalClock: clock);
+            return UnitTestApplication.Start(services);
+        }
+
         private static Mock<ITransition> CreateTarget()
         {
             return CreateTransition(Visual.OpacityProperty);
diff --git a/tests/Avalonia.Base.UnitTests/Data/Core/ExpressionObserverTests_DataValidation.cs b/tests/Avalonia.Base.UnitTests/Data/Core/ExpressionObserverTests_DataValidation.cs
index ecc43aa3a5..43192584af 100644
--- a/tests/Avalonia.Base.UnitTests/Data/Core/ExpressionObserverTests_DataValidation.cs
+++ b/tests/Avalonia.Base.UnitTests/Data/Core/ExpressionObserverTests_DataValidation.cs
@@ -6,6 +6,7 @@ using System.Reactive.Linq;
 using Avalonia.Data;
 using Avalonia.Data.Core;
 using Avalonia.Markup.Parsers;
+using Avalonia.Threading;
 using Avalonia.UnitTests;
 using Xunit;
 
@@ -67,6 +68,8 @@ namespace Avalonia.Base.UnitTests.Data.Core
 
             Assert.Equal(1, data.ErrorsChangedSubscriptionCount);
             sub.Dispose();
+            // Forces WeakEvent compact
+            Dispatcher.UIThread.RunJobs();
             Assert.Equal(0, data.ErrorsChangedSubscriptionCount);
         }
 
diff --git a/tests/Avalonia.Base.UnitTests/Data/Core/ExpressionObserverTests_Indexer.cs b/tests/Avalonia.Base.UnitTests/Data/Core/ExpressionObserverTests_Indexer.cs
index 6289ec46c7..20a4cb6d98 100644
--- a/tests/Avalonia.Base.UnitTests/Data/Core/ExpressionObserverTests_Indexer.cs
+++ b/tests/Avalonia.Base.UnitTests/Data/Core/ExpressionObserverTests_Indexer.cs
@@ -9,6 +9,7 @@ using Avalonia.Data.Core;
 using Avalonia.UnitTests;
 using Xunit;
 using Avalonia.Markup.Parsers;
+using Avalonia.Threading;
 
 namespace Avalonia.Base.UnitTests.Data.Core
 {
@@ -110,6 +111,9 @@ namespace Avalonia.Base.UnitTests.Data.Core
                 data.Foo.Add("baz");
             }
 
+            // Forces WeakEvent compact
+            Dispatcher.UIThread.RunJobs();
+            
             Assert.Equal(new[] { AvaloniaProperty.UnsetValue, "baz" }, result);
             Assert.Null(((INotifyCollectionChangedDebug)data.Foo).GetCollectionChangedSubscribers());
 
@@ -127,6 +131,8 @@ namespace Avalonia.Base.UnitTests.Data.Core
             {
                 data.Foo.RemoveAt(0);
             }
+            // Forces WeakEvent compact
+            Dispatcher.UIThread.RunJobs();
 
             Assert.Equal(new[] { "foo", "bar" }, result);
             Assert.Null(((INotifyCollectionChangedDebug)data.Foo).GetCollectionChangedSubscribers());
@@ -145,6 +151,9 @@ namespace Avalonia.Base.UnitTests.Data.Core
             {
                 data.Foo[1] = "baz";
             }
+            
+            // Forces WeakEvent compact
+            Dispatcher.UIThread.RunJobs();
 
             Assert.Equal(new[] { "bar", "baz" }, result);
             Assert.Null(((INotifyCollectionChangedDebug)data.Foo).GetCollectionChangedSubscribers());
@@ -202,6 +211,9 @@ namespace Avalonia.Base.UnitTests.Data.Core
                 data.Foo["foo"] = "bar2";
             }
 
+            // Forces WeakEvent compact
+            Dispatcher.UIThread.RunJobs();
+            
             var expected = new[] { "bar", "bar2" };
             Assert.Equal(expected, result);
             Assert.Equal(0, data.Foo.PropertyChangedSubscriptionCount);
diff --git a/tests/Avalonia.Base.UnitTests/Data/Core/ExpressionObserverTests_Observable.cs b/tests/Avalonia.Base.UnitTests/Data/Core/ExpressionObserverTests_Observable.cs
index a70d4574a6..4f88d2de7c 100644
--- a/tests/Avalonia.Base.UnitTests/Data/Core/ExpressionObserverTests_Observable.cs
+++ b/tests/Avalonia.Base.UnitTests/Data/Core/ExpressionObserverTests_Observable.cs
@@ -5,6 +5,7 @@ using System.Reactive.Subjects;
 using Avalonia.Data;
 using Avalonia.Data.Core;
 using Avalonia.Markup.Parsers;
+using Avalonia.Threading;
 using Avalonia.UnitTests;
 using Xunit;
 
@@ -68,6 +69,8 @@ namespace Avalonia.Base.UnitTests.Data.Core
                 Assert.Equal(new[] { "foo" }, result);
 
                 sub.Dispose();
+                // Forces WeakEvent compact
+                Dispatcher.UIThread.RunJobs();
                 Assert.Equal(0, data.PropertyChangedSubscriptionCount);
 
                 GC.KeepAlive(data);
@@ -109,10 +112,16 @@ namespace Avalonia.Base.UnitTests.Data.Core
                 var sub = target.Subscribe(x => result.Add(x));
                 data1.Next.OnNext(data2);
                 sync.ExecutePostedCallbacks();
-
+                
+                // Forces WeakEvent compact
+                Dispatcher.UIThread.RunJobs();
                 Assert.Equal(new[] { new BindingNotification("foo") }, result);
 
                 sub.Dispose();
+                
+                // Forces WeakEvent compact
+                Dispatcher.UIThread.RunJobs();
+                
                 Assert.Equal(0, data1.PropertyChangedSubscriptionCount);
 
                 GC.KeepAlive(data1);
diff --git a/tests/Avalonia.Base.UnitTests/Data/Core/ExpressionObserverTests_Property.cs b/tests/Avalonia.Base.UnitTests/Data/Core/ExpressionObserverTests_Property.cs
index 32cdd21e04..a9c62a3c4a 100644
--- a/tests/Avalonia.Base.UnitTests/Data/Core/ExpressionObserverTests_Property.cs
+++ b/tests/Avalonia.Base.UnitTests/Data/Core/ExpressionObserverTests_Property.cs
@@ -10,6 +10,7 @@ using Avalonia.UnitTests;
 using Xunit;
 using System.Threading.Tasks;
 using Avalonia.Markup.Parsers;
+using Avalonia.Threading;
 
 namespace Avalonia.Base.UnitTests.Data.Core
 {
@@ -182,6 +183,9 @@ namespace Avalonia.Base.UnitTests.Data.Core
 
             sub.Dispose();
 
+            // Forces WeakEvent compact
+            Dispatcher.UIThread.RunJobs();
+            
             Assert.Equal(0, data.PropertyChangedSubscriptionCount);
 
             GC.KeepAlive(data);
@@ -209,8 +213,11 @@ namespace Avalonia.Base.UnitTests.Data.Core
             data.RaisePropertyChanged(null);
 
             Assert.Equal(new[] { "foo", "bar", "bar" }, result);
-
+            
             sub.Dispose();
+            
+            // Forces WeakEvent compact
+            Dispatcher.UIThread.RunJobs();
 
             Assert.Equal(0, data.PropertyChangedSubscriptionCount);
 
@@ -231,7 +238,9 @@ namespace Avalonia.Base.UnitTests.Data.Core
             Assert.Equal(new[] { "bar", "baz", null }, result);
 
             sub.Dispose();
-
+            // Forces WeakEvent compact
+            Dispatcher.UIThread.RunJobs();
+            
             Assert.Equal(0, data.PropertyChangedSubscriptionCount);
             Assert.Equal(0, data.Next.PropertyChangedSubscriptionCount);
 
@@ -253,6 +262,9 @@ namespace Avalonia.Base.UnitTests.Data.Core
             Assert.Equal(new[] { "bar", "baz", null }, result);
 
             sub.Dispose();
+            
+            // Forces WeakEvent compact
+            Dispatcher.UIThread.RunJobs();
 
             Assert.Equal(0, data.PropertyChangedSubscriptionCount);
             Assert.Equal(0, data.Next.PropertyChangedSubscriptionCount);
@@ -297,6 +309,9 @@ namespace Avalonia.Base.UnitTests.Data.Core
 
             sub.Dispose();
 
+            // Forces WeakEvent compact
+            Dispatcher.UIThread.RunJobs();
+            
             Assert.Equal(0, data.PropertyChangedSubscriptionCount);
             Assert.Equal(0, data.Next.PropertyChangedSubscriptionCount);
             Assert.Equal(0, old.PropertyChangedSubscriptionCount);
@@ -329,6 +344,9 @@ namespace Avalonia.Base.UnitTests.Data.Core
                 result);
 
             sub.Dispose();
+            
+            // Forces WeakEvent compact
+            Dispatcher.UIThread.RunJobs();
 
             Assert.Equal(0, data.PropertyChangedSubscriptionCount);
             Assert.Equal(0, data.Next.PropertyChangedSubscriptionCount);
@@ -412,6 +430,9 @@ namespace Avalonia.Base.UnitTests.Data.Core
             sub1.Dispose();
             sub2.Dispose();
 
+            // Forces WeakEvent compact
+            Dispatcher.UIThread.RunJobs();
+            
             Assert.Equal(0, data.PropertyChangedSubscriptionCount);
 
             GC.KeepAlive(data);
@@ -535,6 +556,8 @@ namespace Avalonia.Base.UnitTests.Data.Core
                 },
                 result);
 
+            // Forces WeakEvent compact
+            Dispatcher.UIThread.RunJobs();
             Assert.Equal(0, first.PropertyChangedSubscriptionCount);
             Assert.Equal(0, second.PropertyChangedSubscriptionCount);
 
diff --git a/tests/Avalonia.Base.UnitTests/Data/Core/Plugins/IndeiValidationPluginTests.cs b/tests/Avalonia.Base.UnitTests/Data/Core/Plugins/IndeiValidationPluginTests.cs
index d8eddf6330..e8f1f38b90 100644
--- a/tests/Avalonia.Base.UnitTests/Data/Core/Plugins/IndeiValidationPluginTests.cs
+++ b/tests/Avalonia.Base.UnitTests/Data/Core/Plugins/IndeiValidationPluginTests.cs
@@ -3,6 +3,7 @@ using System.Collections;
 using System.Collections.Generic;
 using Avalonia.Data;
 using Avalonia.Data.Core.Plugins;
+using Avalonia.Threading;
 using Xunit;
 
 namespace Avalonia.Base.UnitTests.Data.Core.Plugins
@@ -57,6 +58,8 @@ namespace Avalonia.Base.UnitTests.Data.Core.Plugins
             validator.Subscribe(_ => { });
             Assert.Equal(1, data.ErrorsChangedSubscriptionCount);
             validator.Unsubscribe();
+            // Forces WeakEvent compact
+            Dispatcher.UIThread.RunJobs();
             Assert.Equal(0, data.ErrorsChangedSubscriptionCount);
         }
 
diff --git a/tests/Avalonia.Base.UnitTests/WeakEventTests.cs b/tests/Avalonia.Base.UnitTests/WeakEventTests.cs
new file mode 100644
index 0000000000..2663b4858f
--- /dev/null
+++ b/tests/Avalonia.Base.UnitTests/WeakEventTests.cs
@@ -0,0 +1,75 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Avalonia.Utilities;
+using Xunit;
+
+namespace Avalonia.Base.UnitTests
+{
+    public class WeakEventTests
+    {
+        class EventSource
+        {
+            public event EventHandler Event;
+
+            public void Fire()
+            {
+                Event?.Invoke(this, new EventArgs());
+            }
+
+            public static readonly WeakEvent<EventSource, EventArgs> WeakEv = WeakEvent.Register<EventSource>(
+                (t, s) => t.Event += s,
+                (t, s) => t.Event -= s);
+        }
+
+        class Subscriber : IWeakEventSubscriber<EventArgs>
+        {
+            private readonly Action _onEvent;
+
+            public Subscriber(Action onEvent)
+            {
+                _onEvent = onEvent;
+            }
+
+            public void OnEvent(object sender, WeakEvent ev, EventArgs args)
+            {
+                _onEvent?.Invoke();
+            }
+        }
+
+        [Fact]
+        public void EventShouldBePassedToSubscriber()
+        {
+            bool handled = false;
+            var subscriber = new Subscriber(() => handled = true);
+            var source = new EventSource();
+            EventSource.WeakEv.Subscribe(source, subscriber);
+
+            source.Fire();
+            Assert.True(handled);
+        }
+
+ 
+        [Fact]
+        public void EventHandlerShouldNotBeKeptAlive()
+        {
+            bool handled = false;
+            var source = new EventSource();
+            AddSubscriber(source, () => handled = true);
+            for (int c = 0; c < 10; c++)
+            {
+                GC.Collect();
+                GC.Collect(3, GCCollectionMode.Forced, true);
+            }
+            source.Fire();
+            Assert.False(handled);
+        }
+
+        private void AddSubscriber(EventSource source, Action func)
+        {
+            EventSource.WeakEv.Subscribe(source, new Subscriber(func));
+        }
+    }
+}
diff --git a/tests/Avalonia.LeakTests/AvaloniaObjectTests.cs b/tests/Avalonia.LeakTests/AvaloniaObjectTests.cs
index 54f9a87f94..19208b15f3 100644
--- a/tests/Avalonia.LeakTests/AvaloniaObjectTests.cs
+++ b/tests/Avalonia.LeakTests/AvaloniaObjectTests.cs
@@ -1,5 +1,6 @@
 using System;
 using System.Reactive.Subjects;
+using Avalonia.Threading;
 using JetBrains.dotMemoryUnit;
 using Xunit;
 using Xunit.Abstractions;
@@ -56,7 +57,9 @@ namespace Avalonia.LeakTests
 
             completeSource();
             GC.Collect();
-
+            // Forces WeakEvent compact
+            Dispatcher.UIThread.RunJobs();
+            GC.Collect();
             Assert.False(weakSource.IsAlive);
         }
 
diff --git a/tests/Avalonia.Markup.UnitTests/Data/BindingTests.cs b/tests/Avalonia.Markup.UnitTests/Data/BindingTests.cs
index a0dd565a87..055de999e2 100644
--- a/tests/Avalonia.Markup.UnitTests/Data/BindingTests.cs
+++ b/tests/Avalonia.Markup.UnitTests/Data/BindingTests.cs
@@ -12,6 +12,7 @@ using System.Runtime.CompilerServices;
 using Avalonia.UnitTests;
 using Avalonia.Data.Converters;
 using Avalonia.Data.Core;
+using Avalonia.Threading;
 
 namespace Avalonia.Markup.UnitTests.Data
 {
@@ -160,6 +161,9 @@ namespace Avalonia.Markup.UnitTests.Data
             target.Bind(TextBlock.TextProperty, new Binding("Foo", BindingMode.OneTime));
             target.DataContext = source;
 
+            // Forces WeakEvent compact
+            Dispatcher.UIThread.RunJobs();
+            
             Assert.Equal(0, source.SubscriberCount);
         }
 
@@ -608,6 +612,9 @@ namespace Avalonia.Markup.UnitTests.Data
                 root.DataContext = source;
             }
 
+            // Forces WeakEvent compact
+            Dispatcher.UIThread.RunJobs();
+            
             Assert.Equal(0, source.SubscriberCount);
         }
 
diff --git a/tests/Avalonia.Markup.UnitTests/Parsers/ExpressionObserverBuilderTests_Indexer.cs b/tests/Avalonia.Markup.UnitTests/Parsers/ExpressionObserverBuilderTests_Indexer.cs
index 39d6152b69..dbf6ef2ce9 100644
--- a/tests/Avalonia.Markup.UnitTests/Parsers/ExpressionObserverBuilderTests_Indexer.cs
+++ b/tests/Avalonia.Markup.UnitTests/Parsers/ExpressionObserverBuilderTests_Indexer.cs
@@ -10,6 +10,7 @@ using System.Collections.ObjectModel;
 using System.Reactive.Linq;
 using System.Text;
 using System.Threading.Tasks;
+using Avalonia.Threading;
 using Xunit;
 
 namespace Avalonia.Markup.UnitTests.Parsers
@@ -159,7 +160,10 @@ namespace Avalonia.Markup.UnitTests.Parsers
             {
                 data.Foo.Add("baz");
             }
-
+            
+            // Forces WeakEvent compact
+            Dispatcher.UIThread.RunJobs();
+            
             Assert.Equal(new[] { AvaloniaProperty.UnsetValue, "baz" }, result);
             Assert.Null(((INotifyCollectionChangedDebug)data.Foo).GetCollectionChangedSubscribers());
 
@@ -178,6 +182,9 @@ namespace Avalonia.Markup.UnitTests.Parsers
                 data.Foo.RemoveAt(0);
             }
 
+            // Forces WeakEvent compact
+            Dispatcher.UIThread.RunJobs();
+            
             Assert.Equal(new[] { "foo", "bar" }, result);
             Assert.Null(((INotifyCollectionChangedDebug)data.Foo).GetCollectionChangedSubscribers());
 
@@ -196,6 +203,9 @@ namespace Avalonia.Markup.UnitTests.Parsers
                 data.Foo[1] = "baz";
             }
 
+            // Forces WeakEvent compact
+            Dispatcher.UIThread.RunJobs();
+            
             Assert.Equal(new[] { "bar", "baz" }, result);
             Assert.Null(((INotifyCollectionChangedDebug)data.Foo).GetCollectionChangedSubscribers());
 
@@ -252,6 +262,9 @@ namespace Avalonia.Markup.UnitTests.Parsers
                 data.Foo["foo"] = "bar2";
             }
 
+            // Forces WeakEvent compact
+            Dispatcher.UIThread.RunJobs();
+            
             var expected = new[] { "bar", "bar2" };
             Assert.Equal(expected, result);
             Assert.Equal(0, data.Foo.PropertyChangedSubscriptionCount);