diff --git a/.github/ISSUE_TEMPLATE/config.yml b/.github/ISSUE_TEMPLATE/config.yml
index 687355d825..9e28f532be 100644
--- a/.github/ISSUE_TEMPLATE/config.yml
+++ b/.github/ISSUE_TEMPLATE/config.yml
@@ -3,6 +3,6 @@ contact_links:
   - name: Questions, Discussions, Ideas
     url: https://github.com/AvaloniaUI/Avalonia/discussions/new
     about: Please ask and answer questions here.
-  - name: Avalonia Community Support on Gitter
-    url: https://gitter.im/AvaloniaUI/Avalonia
+  - name: Avalonia Community Support on Telegram
+    url: https://t.me/Avalonia
     about: Please ask and answer questions here.
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index dcf95ce33c..cb5a7d7897 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -2,7 +2,7 @@
 
 ## Before You Start
 
-Drop into our [gitter chat room](https://gitter.im/AvaloniaUI/Avalonia) and let us know what you're thinking of doing. We might be able to give you guidance or let you know if someone else is already working on the feature.
+Drop into our [telegram group](https://t.me/Avalonia) or [gitter chat room](https://gitter.im/AvaloniaUI/Avalonia) and let us know what you're thinking of doing. We might be able to give you guidance or let you know if someone else is already working on the feature.
 
 ## Style
 
diff --git a/global.json b/global.json
index e3e652761c..b160e4561d 100644
--- a/global.json
+++ b/global.json
@@ -4,7 +4,7 @@
     },
     "msbuild-sdks": {
         "Microsoft.Build.Traversal": "1.0.43",
-        "MSBuild.Sdk.Extras": "2.0.54",
+        "MSBuild.Sdk.Extras": "3.0.22",
         "AggregatePackage.NuGet.Sdk" : "0.1.12"
     }
 }
diff --git a/samples/ControlCatalog/Pages/DataGridPage.xaml b/samples/ControlCatalog/Pages/DataGridPage.xaml
index 340b3376f5..9c502b7414 100644
--- a/samples/ControlCatalog/Pages/DataGridPage.xaml
+++ b/samples/ControlCatalog/Pages/DataGridPage.xaml
@@ -4,6 +4,12 @@
              x:Class="ControlCatalog.Pages.DataGridPage">
   <UserControl.Resources>
     <local:GDPValueConverter x:Key="GDPConverter" />
+    <DataTemplate x:Key="Demo.DataTemplates.CountryHeader">
+      <StackPanel Orientation="Horizontal" Spacing="5">
+        <PathIcon Height="12" Data="M 255 116 A 1 1 0 0 0 254 117 L 254 130 A 1 1 0 0 0 255 131 A 1 1 0 0 0 256 130 L 256 123.87109 C 256.1125 123.90694 256.2187 123.94195 256.33984 123.97852 C 257.18636 124.23404 258.19155 124.5 259 124.5 C 259.80845 124.5 260.52133 124.2168 261.17773 123.9668 C 261.83414 123.7168 262.43408 123.5 263 123.5 C 263.56592 123.5 264.5612 123.73404 265.37109 123.97852 C 266.18098 124.22299 266.82227 124.4668 266.82227 124.4668 A 0.50005 0.50005 0 0 0 267.5 124 L 267.5 118 A 0.50005 0.50005 0 0 0 267.17773 117.5332 C 267.17773 117.5332 266.50667 117.27701 265.66016 117.02148 C 264.81364 116.76596 263.80845 116.5 263 116.5 C 262.19155 116.5 261.47867 116.7832 260.82227 117.0332 C 260.16586 117.2832 259.56592 117.5 259 117.5 C 258.43408 117.5 257.4388 117.26596 256.62891 117.02148 C 256.39123 116.94974 256.17716 116.87994 255.98047 116.81445 A 1 1 0 0 0 255 116 z M 263 117.5 C 263.56592 117.5 264.5612 117.73404 265.37109 117.97852 C 266.00097 118.16865 266.29646 118.28239 266.5 118.35742 L 266.5 120.29297 C 266.25708 120.21012 265.97978 120.11797 265.66016 120.02148 C 264.81364 119.76596 263.80845 119.5 263 119.5 C 262.19155 119.5 261.47867 119.7832 260.82227 120.0332 C 260.16586 120.2832 259.56592 120.5 259 120.5 C 258.43408 120.5 257.4388 120.26596 256.62891 120.02148 C 256.39971 119.9523 256.19148 119.88388 256 119.82031 L 256 117.87109 C 256.1125 117.90694 256.2187 117.94195 256.33984 117.97852 C 257.18636 118.23404 258.19155 118.5 259 118.5 C 259.80845 118.5 260.52133 118.2168 261.17773 117.9668 C 261.83414 117.7168 262.43408 117.5 263 117.5 z M 263 120.5 C 263.56592 120.5 264.5612 120.73404 265.37109 120.97852 C 265.8714 121.12954 266.2398 121.25641 266.5 121.34961 L 266.5 123.30469 C 266.22286 123.20649 266.12863 123.1629 265.66016 123.02148 C 264.81364 122.76596 263.80845 122.5 263 122.5 C 262.19155 122.5 261.47867 122.7832 260.82227 123.0332 C 260.16586 123.2832 259.56592 123.5 259 123.5 C 258.43408 123.5 257.4388 123.26596 256.62891 123.02148 C 256.39971 122.9523 256.19148 122.88388 256 122.82031 L 256 120.87109 C 256.1125 120.90694 256.2187 120.94195 256.33984 120.97852 C 257.18636 121.23404 258.19155 121.5 259 121.5 C 259.80845 121.5 260.52133 121.2168 261.17773 120.9668 C 261.83414 120.7168 262.43408 120.5 263 120.5 z" />
+        <TextBlock Text="{Binding}"/>
+      </StackPanel>
+    </DataTemplate>
   </UserControl.Resources>
   <UserControl.Styles>
     <Style Selector="DataGridCell.gdp">
@@ -28,7 +34,8 @@
                     DockPanel.Dock="Top"/>
           <DataGrid Name="dataGrid1" Margin="12" CanUserResizeColumns="True" CanUserReorderColumns="True" CanUserSortColumns="True" HeadersVisibility="All">
             <DataGrid.Columns>
-              <DataGridTextColumn Header="Country" Binding="{Binding Name}" Width="6*" MinWidth="400"  />
+              <!-- Using HeaderTemplate -->
+              <DataGridTextColumn Header="Country" HeaderTemplate="{StaticResource Demo.DataTemplates.CountryHeader}" Binding="{Binding Name}" Width="6*" MinWidth="400" />
               <!-- CompiledBinding example of usage. -->
               <DataGridTextColumn Header="Region" Binding="{CompiledBinding Region}" Width="4*" x:DataType="local:Country" />
               <DataGridTextColumn Header="Population" Binding="{Binding Population}" Width="3*" />
diff --git a/samples/ControlCatalog/Pages/DialogsPage.xaml b/samples/ControlCatalog/Pages/DialogsPage.xaml
index 0497fe9c3b..a910962dde 100644
--- a/samples/ControlCatalog/Pages/DialogsPage.xaml
+++ b/samples/ControlCatalog/Pages/DialogsPage.xaml
@@ -2,16 +2,31 @@
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              x:Class="ControlCatalog.Pages.DialogsPage">
   <StackPanel Orientation="Vertical" Spacing="4" Margin="4">
+      <TextBlock Classes="h1"
+                 Text="Picker dialogs" />
+
       <CheckBox Name="UseFilters">Use filters</CheckBox>
       <Button Name="OpenFile">_Open File</Button>
+      <Button Name="OpenMultipleFiles">Open _Multiple File</Button>
       <Button Name="SaveFile">_Save File</Button>
       <Button Name="SelectFolder">Select Fo_lder</Button>
       <Button Name="OpenBoth">Select _Both</Button>
+
+      <TextBlock x:Name="PickerLastResultsVisible"
+                 Classes="h2"
+                 IsVisible="False"
+                 Text="Last picker results:" />
+      <ItemsPresenter x:Name="PickerLastResults" />
+
+      <TextBlock Margin="0, 8, 0, 0"
+                 Classes="h1"
+                 Text="Window dialogs" />
       <Button Name="DecoratedWindow">Decorated _window</Button>
       <Button Name="DecoratedWindowDialog">Decorated w_indow (dialog)</Button>
       <Button Name="Dialog">_Dialog</Button>
       <Button Name="DialogNoTaskbar">Dialog (_No taskbar icon)</Button>
       <Button Name="OwnedWindow">Own_ed window</Button>
       <Button Name="OwnedWindowNoTaskbar">Owned window (No tas_kbar icon)</Button>
+
   </StackPanel>
 </UserControl>
diff --git a/samples/ControlCatalog/Pages/DialogsPage.xaml.cs b/samples/ControlCatalog/Pages/DialogsPage.xaml.cs
index 49921fb7f6..e96b7aff08 100644
--- a/samples/ControlCatalog/Pages/DialogsPage.xaml.cs
+++ b/samples/ControlCatalog/Pages/DialogsPage.xaml.cs
@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Reflection;
 using Avalonia.Controls;
+using Avalonia.Controls.Presenters;
 using Avalonia.Dialogs;
 using Avalonia.Layout;
 using Avalonia.Markup.Xaml;
@@ -16,6 +17,11 @@ namespace ControlCatalog.Pages
         {
             this.InitializeComponent();
 
+            var results = this.FindControl<ItemsPresenter>("PickerLastResults");
+            var resultsVisible = this.FindControl<TextBlock>("PickerLastResultsVisible");
+
+            string lastSelectedDirectory = null;
+
             List<FileDialogFilter> GetFilters()
             {
                 if (this.FindControl<CheckBox>("UseFilters").IsChecked != true)
@@ -34,44 +40,67 @@ namespace ControlCatalog.Pages
                 };
             }
 
-            this.FindControl<Button>("OpenFile").Click += delegate
+            this.FindControl<Button>("OpenFile").Click += async delegate
             {
-                new OpenFileDialog()
+                var result = await new OpenFileDialog()
                 {
                     Title = "Open file",
                     Filters = GetFilters(),
+                    Directory = lastSelectedDirectory,
                     // Almost guaranteed to exist
                     InitialFileName = Assembly.GetEntryAssembly()?.GetModules().FirstOrDefault()?.FullyQualifiedName
                 }.ShowAsync(GetWindow());
+                results.Items = result;
+                resultsVisible.IsVisible = result?.Any() == true;
+            };
+            this.FindControl<Button>("OpenMultipleFiles").Click += async delegate
+            {
+                var result = await new OpenFileDialog()
+                {
+                    Title = "Open multiple files",
+                    Filters = GetFilters(),
+                    Directory = lastSelectedDirectory,
+                    AllowMultiple = true
+                }.ShowAsync(GetWindow());
+                results.Items = result;
+                resultsVisible.IsVisible = result?.Any() == true;
             };
-            this.FindControl<Button>("SaveFile").Click += delegate
+            this.FindControl<Button>("SaveFile").Click += async delegate
             {
-                new SaveFileDialog()
+                var result = await new SaveFileDialog()
                 {
                     Title = "Save file",
                     Filters = GetFilters(),
+                    Directory = lastSelectedDirectory,
                     InitialFileName = "test.txt"
                 }.ShowAsync(GetWindow());
+                results.Items = new[] { result };
+                resultsVisible.IsVisible = result != null;
             };
-            this.FindControl<Button>("SelectFolder").Click += delegate
+            this.FindControl<Button>("SelectFolder").Click += async delegate
             {
-                new OpenFolderDialog()
+                var result = await new OpenFolderDialog()
                 {
                     Title = "Select folder",
+                    Directory = lastSelectedDirectory,
                 }.ShowAsync(GetWindow());
+                lastSelectedDirectory = result;
+                results.Items = new [] { result };
+                resultsVisible.IsVisible = result != null;
             };
             this.FindControl<Button>("OpenBoth").Click += async delegate
             {
-                var res = await new OpenFileDialog()
+                var result = await new OpenFileDialog()
                 {
                     Title = "Select both",
+                    Directory = lastSelectedDirectory,
                     AllowMultiple = true
                 }.ShowManagedAsync(GetWindow(), new ManagedFileDialogOptions
                 {
                     AllowDirectorySelection = true
                 });
-                if (res != null)
-                    Console.WriteLine("Selected: \n" + string.Join("\n", res));
+                results.Items = result;
+                resultsVisible.IsVisible = result?.Any() == true;
             };
             this.FindControl<Button>("DecoratedWindow").Click += delegate
             {
diff --git a/src/Avalonia.Base/Collections/AvaloniaDictionary.cs b/src/Avalonia.Base/Collections/AvaloniaDictionary.cs
index a3c51dc965..e5ee1e1eef 100644
--- a/src/Avalonia.Base/Collections/AvaloniaDictionary.cs
+++ b/src/Avalonia.Base/Collections/AvaloniaDictionary.cs
@@ -6,6 +6,8 @@ using System.ComponentModel;
 using System.Linq;
 using Avalonia.Data.Core;
 
+#nullable enable
+
 namespace Avalonia.Collections
 {
     /// <summary>
@@ -31,12 +33,12 @@ namespace Avalonia.Collections
         /// <summary>
         /// Occurs when the collection changes.
         /// </summary>
-        public event NotifyCollectionChangedEventHandler CollectionChanged;
+        public event NotifyCollectionChangedEventHandler? CollectionChanged;
 
         /// <summary>
         /// Raised when a property on the collection changes.
         /// </summary>
-        public event PropertyChangedEventHandler PropertyChanged;
+        public event PropertyChangedEventHandler? PropertyChanged;
 
         /// <inheritdoc/>
         public int Count => _inner.Count;
diff --git a/src/Avalonia.Base/Collections/AvaloniaList.cs b/src/Avalonia.Base/Collections/AvaloniaList.cs
index 2f1cb2888e..5b8ba108c7 100644
--- a/src/Avalonia.Base/Collections/AvaloniaList.cs
+++ b/src/Avalonia.Base/Collections/AvaloniaList.cs
@@ -6,6 +6,8 @@ using System.ComponentModel;
 using System.Linq;
 using Avalonia.Diagnostics;
 
+#nullable enable
+
 namespace Avalonia.Collections
 {
     /// <summary>
@@ -53,7 +55,7 @@ namespace Avalonia.Collections
     public class AvaloniaList<T> : IAvaloniaList<T>, IList, INotifyCollectionChangedDebug
     {
         private readonly List<T> _inner;
-        private NotifyCollectionChangedEventHandler _collectionChanged;
+        private NotifyCollectionChangedEventHandler? _collectionChanged;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="AvaloniaList{T}"/> class.
@@ -102,7 +104,7 @@ namespace Avalonia.Collections
         /// <summary>
         /// Raised when a property on the collection changes.
         /// </summary>
-        public event PropertyChangedEventHandler PropertyChanged;
+        public event PropertyChangedEventHandler? PropertyChanged;
 
         /// <summary>
         /// Gets the number of items in the collection.
@@ -118,7 +120,7 @@ namespace Avalonia.Collections
         /// Gets or sets a validation routine that can be used to validate items before they are
         /// added.
         /// </summary>
-        public Action<T> Validate { get; set; }
+        public Action<T>? Validate { get; set; }
 
         /// <inheritdoc/>
         bool IList.IsFixedSize => false;
@@ -133,7 +135,7 @@ namespace Avalonia.Collections
         bool ICollection.IsSynchronized => false;
 
         /// <inheritdoc/>
-        object ICollection.SyncRoot => null;
+        object? ICollection.SyncRoot => null;
 
         /// <inheritdoc/>
         bool ICollection<T>.IsReadOnly => false;
@@ -178,10 +180,10 @@ namespace Avalonia.Collections
         /// </summary>
         /// <param name="index">The index.</param>
         /// <returns>The item.</returns>
-        object IList.this[int index]
+        object? IList.this[int index]
         {
             get { return this[index]; }
-            set { this[index] = (T)value; }
+            set { this[index] = (T)value!; }
         }
 
         /// <summary>
@@ -318,7 +320,7 @@ namespace Avalonia.Collections
         /// <param name="items">The items.</param>
         public virtual void InsertRange(int index, IEnumerable<T> items)
         {
-            Contract.Requires<ArgumentNullException>(items != null);
+            _ = items ?? throw new ArgumentNullException(nameof(items));
 
             bool willRaiseCollectionChanged = _collectionChanged != null;
             bool hasValidation = Validate != null;
@@ -333,7 +335,7 @@ namespace Avalonia.Collections
                         {
                             foreach (T item in collection)
                             {
-                                Validate(item);
+                                Validate!(item);
                             }
                         }
 
@@ -354,7 +356,7 @@ namespace Avalonia.Collections
 
                                 if (hasValidation)
                                 {
-                                    Validate(item);
+                                    Validate!(item);
                                 }
 
                                 _inner.Insert(insertIndex++, item);
@@ -372,7 +374,7 @@ namespace Avalonia.Collections
                     if (en.MoveNext())
                     {
                         // Avoid allocating list for collection notification if there is no event subscriptions.
-                        List<T> notificationItems = willRaiseCollectionChanged ?
+                        List<T>? notificationItems = willRaiseCollectionChanged ?
                             new List<T>() :
                             null;
 
@@ -384,19 +386,17 @@ namespace Avalonia.Collections
 
                             if (hasValidation)
                             {
-                                Validate(item);
+                                Validate!(item);
                             }
 
                             _inner.Insert(insertIndex++, item);
 
-                            if (willRaiseCollectionChanged)
-                            {
-                                notificationItems.Add(item);
-                            }
+                            notificationItems?.Add(item);
 
                         } while (en.MoveNext());
 
-                        NotifyAdd(notificationItems, index);
+                        if (notificationItems is not null)
+                            NotifyAdd(notificationItems, index);
                     }
                 }
             }
@@ -501,13 +501,26 @@ namespace Avalonia.Collections
         /// <param name="items">The items.</param>
         public virtual void RemoveAll(IEnumerable<T> items)
         {
-            Contract.Requires<ArgumentNullException>(items != null);
+            _ = items ?? throw new ArgumentNullException(nameof(items));
 
-            foreach (var i in items)
+            var hItems = new HashSet<T>(items);
+
+            int counter = 0;
+            for (int i = _inner.Count - 1; i >= 0; --i)
             {
-                // TODO: Optimize to only send as many notifications as necessary.
-                Remove(i);
+                if (hItems.Contains(_inner[i]))
+                {
+                    counter += 1;
+                }
+                else if(counter > 0)
+                {
+                    RemoveRange(i + 1, counter);
+                    counter = 0;
+                }
             }
+
+            if (counter > 0)
+                RemoveRange(0, counter);
         }
 
         /// <summary>
@@ -537,17 +550,17 @@ namespace Avalonia.Collections
         }
 
         /// <inheritdoc/>
-        int IList.Add(object value)
+        int IList.Add(object? value)
         {
             int index = Count;
-            Add((T)value);
+            Add((T)value!);
             return index;
         }
 
         /// <inheritdoc/>
-        bool IList.Contains(object value)
+        bool IList.Contains(object? value)
         {
-            return Contains((T)value);
+            return Contains((T)value!);
         }
 
         /// <inheritdoc/>
@@ -557,21 +570,21 @@ namespace Avalonia.Collections
         }
 
         /// <inheritdoc/>
-        int IList.IndexOf(object value)
+        int IList.IndexOf(object? value)
         {
-            return IndexOf((T)value);
+            return IndexOf((T)value!);
         }
 
         /// <inheritdoc/>
-        void IList.Insert(int index, object value)
+        void IList.Insert(int index, object? value)
         {
-            Insert(index, (T)value);
+            Insert(index, (T)value!);
         }
 
         /// <inheritdoc/>
-        void IList.Remove(object value)
+        void IList.Remove(object? value)
         {
-            Remove((T)value);
+            Remove((T)value!);
         }
 
         /// <inheritdoc/>
@@ -631,8 +644,7 @@ namespace Avalonia.Collections
                 // We can't cast array of value type to object[], so we don't support
                 // widening of primitive types here.
                 //
-                object[] objects = array as object[];
-                if (objects == null)
+                if (array is not object?[] objects)
                 {
                     throw new ArgumentException("Invalid array type");
                 }
@@ -653,7 +665,7 @@ namespace Avalonia.Collections
         }
 
         /// <inheritdoc/>
-        Delegate[] INotifyCollectionChangedDebug.GetCollectionChangedSubscribers() => _collectionChanged?.GetInvocationList();
+        Delegate[]? INotifyCollectionChangedDebug.GetCollectionChangedSubscribers() => _collectionChanged?.GetInvocationList();
 
         /// <summary>
         /// Raises the <see cref="CollectionChanged"/> event with an add action.
@@ -752,7 +764,7 @@ namespace Avalonia.Collections
 
             public T Current => _innerEnumerator.Current;
 
-            object IEnumerator.Current => Current;
+            object? IEnumerator.Current => Current;
 
             public void Dispose()
             {
diff --git a/src/Avalonia.Base/Collections/AvaloniaListConverter.cs b/src/Avalonia.Base/Collections/AvaloniaListConverter.cs
index f3e22bfe69..444cdec144 100644
--- a/src/Avalonia.Base/Collections/AvaloniaListConverter.cs
+++ b/src/Avalonia.Base/Collections/AvaloniaListConverter.cs
@@ -3,6 +3,8 @@ using System.ComponentModel;
 using System.Globalization;
 using Avalonia.Utilities;
 
+#nullable enable
+
 namespace Avalonia.Collections
 {
     /// <summary>
diff --git a/src/Avalonia.Base/Collections/AvaloniaListExtensions.cs b/src/Avalonia.Base/Collections/AvaloniaListExtensions.cs
index b52829a60f..5f3c3964f7 100644
--- a/src/Avalonia.Base/Collections/AvaloniaListExtensions.cs
+++ b/src/Avalonia.Base/Collections/AvaloniaListExtensions.cs
@@ -5,6 +5,8 @@ using System.Collections.Specialized;
 using System.ComponentModel;
 using System.Reactive.Disposables;
 
+#nullable enable
+
 namespace Avalonia.Collections
 {
     /// <summary>
@@ -194,7 +196,7 @@ namespace Avalonia.Collections
                         tracked.Remove(inpc);
                     }
                 },
-                null);
+                () => throw new NotSupportedException("Collection reset not supported."));
 
             return Disposable.Create(() =>
             {
diff --git a/src/Avalonia.Base/Collections/IAvaloniaList.cs b/src/Avalonia.Base/Collections/IAvaloniaList.cs
index 250d4faeb9..c28fb835e0 100644
--- a/src/Avalonia.Base/Collections/IAvaloniaList.cs
+++ b/src/Avalonia.Base/Collections/IAvaloniaList.cs
@@ -1,5 +1,7 @@
 using System.Collections.Generic;
 
+#nullable enable
+
 namespace Avalonia.Collections
 {
     /// <summary>
diff --git a/src/Avalonia.Base/Collections/IAvaloniaReadOnlyList.cs b/src/Avalonia.Base/Collections/IAvaloniaReadOnlyList.cs
index a6a5953827..09622dceba 100644
--- a/src/Avalonia.Base/Collections/IAvaloniaReadOnlyList.cs
+++ b/src/Avalonia.Base/Collections/IAvaloniaReadOnlyList.cs
@@ -2,6 +2,8 @@ using System.Collections.Generic;
 using System.Collections.Specialized;
 using System.ComponentModel;
 
+#nullable enable
+
 namespace Avalonia.Collections
 {
     /// <summary>
diff --git a/src/Avalonia.Base/Collections/NotifyCollectionChangedExtensions.cs b/src/Avalonia.Base/Collections/NotifyCollectionChangedExtensions.cs
index fe9ef667b0..7a8c2325e6 100644
--- a/src/Avalonia.Base/Collections/NotifyCollectionChangedExtensions.cs
+++ b/src/Avalonia.Base/Collections/NotifyCollectionChangedExtensions.cs
@@ -4,6 +4,8 @@ using System.Reactive.Linq;
 using Avalonia.Reactive;
 using Avalonia.Utilities;
 
+#nullable enable
+
 namespace Avalonia.Collections
 {
     public static class NotifyCollectionChangedExtensions
@@ -16,7 +18,7 @@ namespace Avalonia.Collections
         public static IObservable<NotifyCollectionChangedEventArgs> GetWeakCollectionChangedObservable(
             this INotifyCollectionChanged collection)
         {
-            Contract.Requires<ArgumentNullException>(collection != null);
+            _ = collection ?? throw new ArgumentNullException(nameof(collection));
 
             return new WeakCollectionChangedObservable(new WeakReference<INotifyCollectionChanged>(collection));
         }
@@ -33,8 +35,8 @@ namespace Avalonia.Collections
             this INotifyCollectionChanged collection, 
             NotifyCollectionChangedEventHandler handler)
         {
-            Contract.Requires<ArgumentNullException>(collection != null);
-            Contract.Requires<ArgumentNullException>(handler != null);
+            _ = collection ?? throw new ArgumentNullException(nameof(collection));
+            _ = handler ?? throw new ArgumentNullException(nameof(handler));
 
             return collection.GetWeakCollectionChangedObservable()
                 .Subscribe(e => handler(collection, e));
@@ -52,8 +54,8 @@ namespace Avalonia.Collections
             this INotifyCollectionChanged collection,
             Action<NotifyCollectionChangedEventArgs> handler)
         {
-            Contract.Requires<ArgumentNullException>(collection != null);
-            Contract.Requires<ArgumentNullException>(handler != null);
+            _ = collection ?? throw new ArgumentNullException(nameof(collection));
+            _ = handler ?? throw new ArgumentNullException(nameof(handler));
 
             return collection.GetWeakCollectionChangedObservable().Subscribe(handler);
         }
diff --git a/src/Avalonia.Base/Collections/Pooled/ClearMode.cs b/src/Avalonia.Base/Collections/Pooled/ClearMode.cs
index d78ac8feab..f13538dce3 100644
--- a/src/Avalonia.Base/Collections/Pooled/ClearMode.cs
+++ b/src/Avalonia.Base/Collections/Pooled/ClearMode.cs
@@ -1,6 +1,8 @@
 // This source file is adapted from the Collections.Pooled.
 // (https://github.com/jtmueller/Collections.Pooled/tree/master/Collections.Pooled/)
 
+#nullable enable
+
 namespace Avalonia.Collections.Pooled
 {
     /// <summary>
diff --git a/src/Avalonia.Base/Collections/Pooled/ICollectionDebugView.cs b/src/Avalonia.Base/Collections/Pooled/ICollectionDebugView.cs
index 2b15388a13..6f89cb7728 100644
--- a/src/Avalonia.Base/Collections/Pooled/ICollectionDebugView.cs
+++ b/src/Avalonia.Base/Collections/Pooled/ICollectionDebugView.cs
@@ -6,6 +6,8 @@ using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 
+#nullable enable
+
 namespace Avalonia.Collections.Pooled
 {
     internal sealed class ICollectionDebugView<T>
diff --git a/src/Avalonia.Base/Collections/Pooled/IReadOnlyPooledList.cs b/src/Avalonia.Base/Collections/Pooled/IReadOnlyPooledList.cs
index 7a233a62ab..7ac22d2baf 100644
--- a/src/Avalonia.Base/Collections/Pooled/IReadOnlyPooledList.cs
+++ b/src/Avalonia.Base/Collections/Pooled/IReadOnlyPooledList.cs
@@ -4,6 +4,8 @@
 using System;
 using System.Collections.Generic;
 
+#nullable enable
+
 namespace Avalonia.Collections.Pooled
 {
     /// <summary>
diff --git a/src/Avalonia.Base/Collections/Pooled/PooledList.cs b/src/Avalonia.Base/Collections/Pooled/PooledList.cs
index 2cd9758f12..73cd602948 100644
--- a/src/Avalonia.Base/Collections/Pooled/PooledList.cs
+++ b/src/Avalonia.Base/Collections/Pooled/PooledList.cs
@@ -8,10 +8,13 @@ using System.Collections;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 using System.Runtime.Serialization;
 using System.Threading;
 
+#nullable enable
+
 namespace Avalonia.Collections.Pooled
 {
     /// <summary>
@@ -38,7 +41,7 @@ namespace Avalonia.Collections.Pooled
         [NonSerialized]
         private ArrayPool<T> _pool;
         [NonSerialized]
-        private object _syncRoot;
+        private object? _syncRoot;
 
         private T[] _items; // Do not rename (binary serialization)
         private int _size; // Do not rename (binary serialization)
@@ -375,7 +378,7 @@ namespace Avalonia.Collections.Pooled
             {
                 if (_syncRoot == null)
                 {
-                    Interlocked.CompareExchange<object>(ref _syncRoot, new object(), null);
+                    Interlocked.CompareExchange<object?>(ref _syncRoot, new object(), null);
                 }
                 return _syncRoot;
             }
@@ -407,14 +410,14 @@ namespace Avalonia.Collections.Pooled
             }
         }
 
-        private static bool IsCompatibleObject(object value)
+        private static bool IsCompatibleObject(object? value)
         {
             // Non-null values are fine.  Only accept nulls if T is a class or Nullable<U>.
             // Note that default(T) is not equal to null for value types except when T is Nullable<U>. 
             return ((value is T) || (value == null && default(T) == null));
         }
 
-        object IList.this[int index]
+        object? IList.this[int index]
         {
             get
             {
@@ -426,7 +429,7 @@ namespace Avalonia.Collections.Pooled
 
                 try
                 {
-                    this[index] = (T)value;
+                    this[index] = (T)value!;
                 }
                 catch (InvalidCastException)
                 {
@@ -466,13 +469,13 @@ namespace Avalonia.Collections.Pooled
             _items[size] = item;
         }
 
-        int IList.Add(object item)
+        int IList.Add(object? item)
         {
             ThrowHelper.IfNullAndNullsAreIllegalThenThrow<T>(item, ExceptionArgument.item);
 
             try
             {
-                Add((T)item);
+                Add((T)item!);
             }
             catch (InvalidCastException)
             {
@@ -545,7 +548,7 @@ namespace Avalonia.Collections.Pooled
         /// the search value should be inserted into the list in order for the list
         /// to remain sorted.
         /// </para></remarks>
-        public int BinarySearch(int index, int count, T item, IComparer<T> comparer)
+        public int BinarySearch(int index, int count, T item, IComparer<T>? comparer)
         {
             if (index < 0)
                 ThrowHelper.ThrowIndexArgumentOutOfRange_NeedNonNegNumException();
@@ -608,11 +611,11 @@ namespace Avalonia.Collections.Pooled
             return _size != 0 && IndexOf(item) != -1;
         }
 
-        bool IList.Contains(object item)
+        bool IList.Contains(object? item)
         {
             if (IsCompatibleObject(item))
             {
-                return Contains((T)item);
+                return Contains((T)item!);
             }
             return false;
         }
@@ -693,7 +696,7 @@ namespace Avalonia.Collections.Pooled
         public bool Exists(Func<T, bool> match)
             => FindIndex(match) != -1;
 
-        public bool TryFind(Func<T, bool> match, out T result)
+        public bool TryFind(Func<T, bool> match, [MaybeNullWhen(false)] out T result)
         {
             if (match == null)
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.match);
@@ -753,7 +756,7 @@ namespace Avalonia.Collections.Pooled
             return -1;
         }
 
-        public bool TryFindLast(Func<T, bool> match, out T result)
+        public bool TryFindLast(Func<T, bool> match, [MaybeNullWhen(false)] out T result)
         {
             if (match is null)
             {
@@ -886,11 +889,11 @@ namespace Avalonia.Collections.Pooled
         public int IndexOf(T item)
             => Array.IndexOf(_items, item, 0, _size);
 
-        int IList.IndexOf(object item)
+        int IList.IndexOf(object? item)
         {
             if (IsCompatibleObject(item))
             {
-                return IndexOf((T)item);
+                return IndexOf((T)item!);
             }
             return -1;
         }
@@ -947,13 +950,13 @@ namespace Avalonia.Collections.Pooled
             _version++;
         }
 
-        void IList.Insert(int index, object item)
+        void IList.Insert(int index, object? item)
         {
             ThrowHelper.IfNullAndNullsAreIllegalThenThrow<T>(item, ExceptionArgument.item);
 
             try
             {
-                Insert(index, (T)item);
+                Insert(index, (T)item!);
             }
             catch (InvalidCastException)
             {
@@ -1155,11 +1158,11 @@ namespace Avalonia.Collections.Pooled
             return false;
         }
 
-        void IList.Remove(object item)
+        void IList.Remove(object? item)
         {
             if (IsCompatibleObject(item))
             {
-                Remove((T)item);
+                Remove((T)item!);
             }
         }
 
@@ -1225,7 +1228,7 @@ namespace Avalonia.Collections.Pooled
             if (_clearOnFree)
             {
                 // Clear the removed element so that the gc can reclaim the reference.
-                _items[_size] = default;
+                _items[_size] = default!;
             }
         }
 
@@ -1315,7 +1318,7 @@ namespace Avalonia.Collections.Pooled
         /// 
         /// This method uses the Array.Sort method to sort the elements.
         /// </summary>
-        public void Sort(int index, int count, IComparer<T> comparer)
+        public void Sort(int index, int count, IComparer<T>? comparer)
         {
             if (index < 0)
                 ThrowHelper.ThrowIndexArgumentOutOfRange_NeedNonNegNumException();
@@ -1452,7 +1455,7 @@ namespace Avalonia.Collections.Pooled
             private readonly PooledList<T> _list;
             private int _index;
             private readonly int _version;
-            private T _current;
+            private T? _current;
 
             internal Enumerator(PooledList<T> list)
             {
@@ -1491,9 +1494,9 @@ namespace Avalonia.Collections.Pooled
                 return false;
             }
 
-            public T Current => _current;
+            public T Current => _current!;
 
-            object IEnumerator.Current
+            object? IEnumerator.Current
             {
                 get
                 {
diff --git a/src/Avalonia.Base/Collections/Pooled/PooledStack.cs b/src/Avalonia.Base/Collections/Pooled/PooledStack.cs
index 104a7f97e9..8a03c6f5e4 100644
--- a/src/Avalonia.Base/Collections/Pooled/PooledStack.cs
+++ b/src/Avalonia.Base/Collections/Pooled/PooledStack.cs
@@ -20,6 +20,8 @@ using System.Runtime.CompilerServices;
 using System.Runtime.Serialization;
 using System.Threading;
 
+#nullable enable
+
 namespace Avalonia.Collections.Pooled
 {
     /// <summary>
@@ -34,7 +36,7 @@ namespace Avalonia.Collections.Pooled
         [NonSerialized]
         private ArrayPool<T> _pool;
         [NonSerialized]
-        private object _syncRoot;
+        private object? _syncRoot;
 
         private T[] _array; // Storage for stack elements. Do not rename (binary serialization)
         private int _size; // Number of items in the stack. Do not rename (binary serialization)
@@ -237,7 +239,7 @@ namespace Avalonia.Collections.Pooled
             {
                 if (_syncRoot == null)
                 {
-                    Interlocked.CompareExchange<object>(ref _syncRoot, new object(), null);
+                    Interlocked.CompareExchange<object?>(ref _syncRoot, new object(), null);
                 }
                 return _syncRoot;
             }
@@ -456,7 +458,7 @@ namespace Avalonia.Collections.Pooled
             return array[size];
         }
 
-        public bool TryPeek(out T result)
+        public bool TryPeek([MaybeNullWhen(false)] out T result)
         {
             int size = _size - 1;
             T[] array = _array;
@@ -492,12 +494,12 @@ namespace Avalonia.Collections.Pooled
             T item = array[size];
             if (_clearOnFree)
             {
-                array[size] = default;     // Free memory quicker.
+                array[size] = default!;     // Free memory quicker.
             }
             return item;
         }
 
-        public bool TryPop(out T result)
+        public bool TryPop([MaybeNullWhen(false)] out T result)
         {
             int size = _size - 1;
             T[] array = _array;
@@ -513,7 +515,7 @@ namespace Avalonia.Collections.Pooled
             result = array[size];
             if (_clearOnFree)
             {
-                array[size] = default;     // Free memory quicker.
+                array[size] = default!;     // Free memory quicker.
             }
             return true;
         }
@@ -574,7 +576,7 @@ namespace Avalonia.Collections.Pooled
             throw new InvalidOperationException("Stack was empty.");
         }
 
-        private void ReturnArray(T[] replaceWith = null)
+        private void ReturnArray(T[]? replaceWith = null)
         {
             if (_array?.Length > 0)
             {
@@ -625,7 +627,7 @@ namespace Avalonia.Collections.Pooled
             private readonly PooledStack<T> _stack;
             private readonly int _version;
             private int _index;
-            private T _currentElement;
+            private T? _currentElement;
 
             internal Enumerator(PooledStack<T> stack)
             {
@@ -672,7 +674,7 @@ namespace Avalonia.Collections.Pooled
                 {
                     if (_index < 0)
                         ThrowEnumerationNotStartedOrEnded();
-                    return _currentElement;
+                    return _currentElement!;
                 }
             }
 
@@ -682,7 +684,7 @@ namespace Avalonia.Collections.Pooled
                 throw new InvalidOperationException(_index == -2 ? "Enumeration was not started." : "Enumeration has ended.");
             }
 
-            object IEnumerator.Current
+            object? IEnumerator.Current
             {
                 get { return Current; }
             }
diff --git a/src/Avalonia.Base/Collections/Pooled/StackDebugView.cs b/src/Avalonia.Base/Collections/Pooled/StackDebugView.cs
index b042388079..b55ac110c6 100644
--- a/src/Avalonia.Base/Collections/Pooled/StackDebugView.cs
+++ b/src/Avalonia.Base/Collections/Pooled/StackDebugView.cs
@@ -5,6 +5,8 @@
 using System;
 using System.Diagnostics;
 
+#nullable enable
+
 namespace Avalonia.Collections.Pooled
 {
     internal sealed class StackDebugView<T>
diff --git a/src/Avalonia.Base/Collections/Pooled/ThrowHelper.cs b/src/Avalonia.Base/Collections/Pooled/ThrowHelper.cs
index 74558229c3..3237286107 100644
--- a/src/Avalonia.Base/Collections/Pooled/ThrowHelper.cs
+++ b/src/Avalonia.Base/Collections/Pooled/ThrowHelper.cs
@@ -38,108 +38,128 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 using System.Runtime.Serialization;
 
+#nullable enable
+
 namespace Avalonia.Collections.Pooled
 {
     internal static class ThrowHelper
     {
+        [DoesNotReturn]
         internal static void ThrowArrayTypeMismatchException()
         {
             throw new ArrayTypeMismatchException();
         }
 
+        [DoesNotReturn]
         internal static void ThrowIndexOutOfRangeException()
         {
             throw new IndexOutOfRangeException();
         }
 
+        [DoesNotReturn]
         internal static void ThrowArgumentOutOfRangeException()
         {
             throw new ArgumentOutOfRangeException();
         }
 
+        [DoesNotReturn]
         internal static void ThrowArgumentException_DestinationTooShort()
         {
             throw new ArgumentException("Destination too short.");
         }
 
+        [DoesNotReturn]
         internal static void ThrowArgumentException_OverlapAlignmentMismatch()
         {
             throw new ArgumentException("Overlap alignment mismatch.");
         }
 
+        [DoesNotReturn]
         internal static void ThrowArgumentOutOfRange_IndexException()
         {
             throw GetArgumentOutOfRangeException(ExceptionArgument.index,
                                                     ExceptionResource.ArgumentOutOfRange_Index);
         }
 
+        [DoesNotReturn]
         internal static void ThrowIndexArgumentOutOfRange_NeedNonNegNumException()
         {
             throw GetArgumentOutOfRangeException(ExceptionArgument.index,
                                                     ExceptionResource.ArgumentOutOfRange_NeedNonNegNum);
         }
 
+        [DoesNotReturn]
         internal static void ThrowValueArgumentOutOfRange_NeedNonNegNumException()
         {
             throw GetArgumentOutOfRangeException(ExceptionArgument.value,
                                                     ExceptionResource.ArgumentOutOfRange_NeedNonNegNum);
         }
 
+        [DoesNotReturn]
         internal static void ThrowLengthArgumentOutOfRange_ArgumentOutOfRange_NeedNonNegNum()
         {
             throw GetArgumentOutOfRangeException(ExceptionArgument.length,
                                                     ExceptionResource.ArgumentOutOfRange_NeedNonNegNum);
         }
 
+        [DoesNotReturn]
         internal static void ThrowStartIndexArgumentOutOfRange_ArgumentOutOfRange_Index()
         {
             throw GetArgumentOutOfRangeException(ExceptionArgument.startIndex,
                                                     ExceptionResource.ArgumentOutOfRange_Index);
         }
 
+        [DoesNotReturn]
         internal static void ThrowCountArgumentOutOfRange_ArgumentOutOfRange_Count()
         {
             throw GetArgumentOutOfRangeException(ExceptionArgument.count,
                                                     ExceptionResource.ArgumentOutOfRange_Count);
         }
 
+        [DoesNotReturn]
         internal static void ThrowWrongKeyTypeArgumentException<T>(T key, Type targetType)
         {
             // Generic key to move the boxing to the right hand side of throw
-            throw GetWrongKeyTypeArgumentException((object)key, targetType);
+            throw GetWrongKeyTypeArgumentException((object?)key, targetType);
         }
 
+        [DoesNotReturn]
         internal static void ThrowWrongValueTypeArgumentException<T>(T value, Type targetType)
         {
             // Generic key to move the boxing to the right hand side of throw
-            throw GetWrongValueTypeArgumentException((object)value, targetType);
+            throw GetWrongValueTypeArgumentException((object?)value, targetType);
         }
 
-        private static ArgumentException GetAddingDuplicateWithKeyArgumentException(object key)
+        private static ArgumentException GetAddingDuplicateWithKeyArgumentException(object? key)
         {
             return new ArgumentException($"Error adding duplicate with key: {key}.");
         }
 
+        [DoesNotReturn]
         internal static void ThrowAddingDuplicateWithKeyArgumentException<T>(T key)
         {
             // Generic key to move the boxing to the right hand side of throw
-            throw GetAddingDuplicateWithKeyArgumentException((object)key);
+            throw GetAddingDuplicateWithKeyArgumentException((object?)key);
         }
 
+        [DoesNotReturn]
         internal static void ThrowKeyNotFoundException<T>(T key)
         {
             // Generic key to move the boxing to the right hand side of throw
-            throw GetKeyNotFoundException((object)key);
+            throw GetKeyNotFoundException((object?)key);
         }
 
+        [DoesNotReturn]
         internal static void ThrowArgumentException(ExceptionResource resource)
         {
             throw GetArgumentException(resource);
         }
 
+        [DoesNotReturn]
         internal static void ThrowArgumentException(ExceptionResource resource, ExceptionArgument argument)
         {
             throw GetArgumentException(resource, argument);
@@ -150,141 +170,169 @@ namespace Avalonia.Collections.Pooled
             return new ArgumentNullException(GetArgumentName(argument));
         }
 
+        [DoesNotReturn]
         internal static void ThrowArgumentNullException(ExceptionArgument argument)
         {
             throw GetArgumentNullException(argument);
         }
 
+        [DoesNotReturn]
         internal static void ThrowArgumentNullException(ExceptionResource resource)
         {
             throw new ArgumentNullException(GetResourceString(resource));
         }
 
+        [DoesNotReturn]
         internal static void ThrowArgumentNullException(ExceptionArgument argument, ExceptionResource resource)
         {
             throw new ArgumentNullException(GetArgumentName(argument), GetResourceString(resource));
         }
 
+        [DoesNotReturn]
         internal static void ThrowArgumentOutOfRangeException(ExceptionArgument argument)
         {
             throw new ArgumentOutOfRangeException(GetArgumentName(argument));
         }
 
+        [DoesNotReturn]
         internal static void ThrowArgumentOutOfRangeException(ExceptionArgument argument, ExceptionResource resource)
         {
             throw GetArgumentOutOfRangeException(argument, resource);
         }
 
+        [DoesNotReturn]
         internal static void ThrowArgumentOutOfRangeException(ExceptionArgument argument, int paramNumber, ExceptionResource resource)
         {
             throw GetArgumentOutOfRangeException(argument, paramNumber, resource);
         }
 
+        [DoesNotReturn]
         internal static void ThrowInvalidOperationException(ExceptionResource resource)
         {
             throw GetInvalidOperationException(resource);
         }
 
+        [DoesNotReturn]
         internal static void ThrowInvalidOperationException(ExceptionResource resource, Exception e)
         {
             throw new InvalidOperationException(GetResourceString(resource), e);
         }
 
+        [DoesNotReturn]
         internal static void ThrowSerializationException(ExceptionResource resource)
         {
             throw new SerializationException(GetResourceString(resource));
         }
 
+        [DoesNotReturn]
         internal static void ThrowSecurityException(ExceptionResource resource)
         {
             throw new System.Security.SecurityException(GetResourceString(resource));
         }
 
+        [DoesNotReturn]
         internal static void ThrowRankException(ExceptionResource resource)
         {
             throw new RankException(GetResourceString(resource));
         }
 
+        [DoesNotReturn]
         internal static void ThrowNotSupportedException(ExceptionResource resource)
         {
             throw new NotSupportedException(GetResourceString(resource));
         }
 
+        [DoesNotReturn]
         internal static void ThrowUnauthorizedAccessException(ExceptionResource resource)
         {
             throw new UnauthorizedAccessException(GetResourceString(resource));
         }
 
+        [DoesNotReturn]
         internal static void ThrowObjectDisposedException(string objectName, ExceptionResource resource)
         {
             throw new ObjectDisposedException(objectName, GetResourceString(resource));
         }
 
+        [DoesNotReturn]
         internal static void ThrowObjectDisposedException(ExceptionResource resource)
         {
             throw new ObjectDisposedException(null, GetResourceString(resource));
         }
 
+        [DoesNotReturn]
         internal static void ThrowNotSupportedException()
         {
             throw new NotSupportedException();
         }
 
+        [DoesNotReturn]
         internal static void ThrowAggregateException(List<Exception> exceptions)
         {
             throw new AggregateException(exceptions);
         }
 
+        [DoesNotReturn]
         internal static void ThrowOutOfMemoryException()
         {
             throw new OutOfMemoryException();
         }
 
+        [DoesNotReturn]
         internal static void ThrowArgumentException_Argument_InvalidArrayType()
         {
             throw new ArgumentException("Invalid array type.");
         }
 
+        [DoesNotReturn]
         internal static void ThrowInvalidOperationException_InvalidOperation_EnumNotStarted()
         {
             throw new InvalidOperationException("Enumeration has not started.");
         }
 
+        [DoesNotReturn]
         internal static void ThrowInvalidOperationException_InvalidOperation_EnumEnded()
         {
             throw new InvalidOperationException("Enumeration has ended.");
         }
 
+        [DoesNotReturn]
         internal static void ThrowInvalidOperationException_EnumCurrent(int index)
         {
             throw GetInvalidOperationException_EnumCurrent(index);
         }
 
+        [DoesNotReturn]
         internal static void ThrowInvalidOperationException_InvalidOperation_EnumFailedVersion()
         {
             throw new InvalidOperationException("Collection was modified during enumeration.");
         }
 
+        [DoesNotReturn]
         internal static void ThrowInvalidOperationException_InvalidOperation_EnumOpCantHappen()
         {
             throw new InvalidOperationException("Invalid enumerator state: enumeration cannot proceed.");
         }
 
+        [DoesNotReturn]
         internal static void ThrowInvalidOperationException_InvalidOperation_NoValue()
         {
             throw new InvalidOperationException("No value provided.");
         }
 
+        [DoesNotReturn]
         internal static void ThrowInvalidOperationException_ConcurrentOperationsNotSupported()
         {
             throw new InvalidOperationException("Concurrent operations are not supported.");
         }
 
+        [DoesNotReturn]
         internal static void ThrowInvalidOperationException_HandleIsNotInitialized()
         {
             throw new InvalidOperationException("Handle is not initialized.");
         }
 
+        [DoesNotReturn]
         internal static void ThrowFormatException_BadFormatSpecifier()
         {
             throw new FormatException("Bad format specifier.");
@@ -300,17 +348,17 @@ namespace Avalonia.Collections.Pooled
             return new InvalidOperationException(GetResourceString(resource));
         }
 
-        private static ArgumentException GetWrongKeyTypeArgumentException(object key, Type targetType)
+        private static ArgumentException GetWrongKeyTypeArgumentException(object? key, Type targetType)
         {
             return new ArgumentException($"Wrong key type. Expected {targetType}, got: '{key}'.", nameof(key));
         }
 
-        private static ArgumentException GetWrongValueTypeArgumentException(object value, Type targetType)
+        private static ArgumentException GetWrongValueTypeArgumentException(object? value, Type targetType)
         {
             return new ArgumentException($"Wrong value type. Expected {targetType}, got: '{value}'.", nameof(value));
         }
 
-        private static KeyNotFoundException GetKeyNotFoundException(object key)
+        private static KeyNotFoundException GetKeyNotFoundException(object? key)
         {
             return new KeyNotFoundException($"Key not found: {key}");
         }
@@ -342,7 +390,7 @@ namespace Avalonia.Collections.Pooled
         // Aggressively inline so the jit evaluates the if in place and either drops the call altogether
         // Or just leaves null test and call to the Non-returning ThrowHelper.ThrowArgumentNullException
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        internal static void IfNullAndNullsAreIllegalThenThrow<T>(object value, ExceptionArgument argName)
+        internal static void IfNullAndNullsAreIllegalThenThrow<T>(object? value, ExceptionArgument argName)
         {
             // Note that default(T) is not equal to null for value types except when T is Nullable<U>.
             if (!(default(T) == null) && value == null)
diff --git a/src/Avalonia.Controls.DataGrid/DataGridColumn.cs b/src/Avalonia.Controls.DataGrid/DataGridColumn.cs
index 5499257171..4c4bc4f53b 100644
--- a/src/Avalonia.Controls.DataGrid/DataGridColumn.cs
+++ b/src/Avalonia.Controls.DataGrid/DataGridColumn.cs
@@ -12,7 +12,9 @@ using System;
 using System.ComponentModel;
 using System.Linq;
 using System.Diagnostics;
+using Avalonia.Controls.Templates;
 using Avalonia.Controls.Utils;
+using Avalonia.Layout;
 using Avalonia.Markup.Xaml.MarkupExtensions;
 
 namespace Avalonia.Controls
@@ -29,6 +31,7 @@ namespace Avalonia.Controls
         private bool _settingWidthInternally;
         private int _displayIndexWithFiller;
         private object _header;
+        private IDataTemplate _headerTemplate;
         private DataGridColumnHeader _headerCell;
         private IControl _editingElement;
         private ICellEditBinding _editBinding;
@@ -416,6 +419,28 @@ namespace Avalonia.Controls
             }
         }
 
+        /// <summary>
+        ///  Gets or sets an <see cref="IDataTemplate"/> for the <see cref="Header"/>
+        /// </summary>
+        public IDataTemplate HeaderTemplate
+        {
+            get
+            {
+                return _headerTemplate;
+            }
+            set
+            {
+                if (_headerTemplate != value)
+                {
+                    _headerTemplate = value;
+                    if (_headerCell != null)
+                    {
+                        _headerCell.ContentTemplate = value;
+                    }
+                }
+            }
+        }
+        
         public bool IsAutoGenerated
         {
             get;
@@ -834,9 +859,9 @@ namespace Avalonia.Controls
         {
             if (OwningGrid != null && OwningGrid.UseLayoutRounding)
             {
-                double roundedLeftEdge = Math.Floor(leftEdge + 0.5);
-                double roundedRightEdge = Math.Floor(leftEdge + ActualWidth + 0.5);
-                LayoutRoundedWidth = roundedRightEdge - roundedLeftEdge;
+                var scale = LayoutHelper.GetLayoutScale(HeaderCell);
+                var roundSize = LayoutHelper.RoundLayoutSize(new Size(leftEdge + ActualWidth, 1), scale, scale);
+                LayoutRoundedWidth = roundSize.Width - leftEdge;
             }
             else
             {
@@ -850,7 +875,8 @@ namespace Avalonia.Controls
             var result = new DataGridColumnHeader
             {
                 OwningColumn = this,
-                Content = _header
+                Content = _header,
+                ContentTemplate = _headerTemplate
             };
             //result.EnsureStyle(null);
 
diff --git a/src/Avalonia.Controls.DataGrid/Themes/Default.xaml b/src/Avalonia.Controls.DataGrid/Themes/Default.xaml
index ca0873e183..6715b7ceb9 100644
--- a/src/Avalonia.Controls.DataGrid/Themes/Default.xaml
+++ b/src/Avalonia.Controls.DataGrid/Themes/Default.xaml
@@ -47,7 +47,8 @@
                 HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                 VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
                 Margin="{TemplateBinding Padding}">
-            <ContentPresenter Content="{TemplateBinding Content}"/>
+            <ContentPresenter Content="{TemplateBinding Content}" 
+                              ContentTemplate="{TemplateBinding ContentTemplate}" />
 
             <Path Name="SortIcon"
                   Grid.Column="1"
diff --git a/src/Avalonia.Controls.DataGrid/Themes/Fluent.xaml b/src/Avalonia.Controls.DataGrid/Themes/Fluent.xaml
index 8ccf717d94..432fe2c0bf 100644
--- a/src/Avalonia.Controls.DataGrid/Themes/Fluent.xaml
+++ b/src/Avalonia.Controls.DataGrid/Themes/Fluent.xaml
@@ -193,7 +193,8 @@
                                 Width="Auto" />
             </Grid.ColumnDefinitions>
 
-            <ContentPresenter Content="{TemplateBinding Content}" />
+            <ContentPresenter Content="{TemplateBinding Content}" 
+                              ContentTemplate="{TemplateBinding ContentTemplate}" />
 
             <Path Name="SortIcon"
                   Grid.Column="1"
diff --git a/src/Avalonia.Controls/Border.cs b/src/Avalonia.Controls/Border.cs
index 0c6949465b..ee67f303f3 100644
--- a/src/Avalonia.Controls/Border.cs
+++ b/src/Avalonia.Controls/Border.cs
@@ -1,3 +1,5 @@
+using Avalonia.Collections;
+using Avalonia.Controls.Shapes;
 using Avalonia.Controls.Utils;
 using Avalonia.Layout;
 using Avalonia.Media;
@@ -41,7 +43,31 @@ namespace Avalonia.Controls
         /// </summary>
         public static readonly StyledProperty<BoxShadows> BoxShadowProperty =
             AvaloniaProperty.Register<Border, BoxShadows>(nameof(BoxShadow));
-        
+
+        /// <summary>
+        /// Defines the <see cref="BorderDashOffset"/> property.
+        /// </summary>
+        public static readonly StyledProperty<double> BorderDashOffsetProperty =
+            AvaloniaProperty.Register<Border, double>(nameof(BorderDashOffset));
+
+        /// <summary>
+        /// Defines the <see cref="BorderDashArray"/> property.
+        /// </summary>
+        public static readonly StyledProperty<AvaloniaList<double>?> BorderDashArrayProperty =
+            AvaloniaProperty.Register<Border, AvaloniaList<double>?>(nameof(BorderDashArray));
+
+        /// <summary>
+        /// Defines the <see cref="BorderLineCap"/> property.
+        /// </summary>
+        public static readonly StyledProperty<PenLineCap> BorderLineCapProperty =
+            AvaloniaProperty.Register<Border, PenLineCap>(nameof(BorderLineCap), PenLineCap.Flat);
+
+        /// <summary>
+        /// Defines the <see cref="BorderLineJoin"/> property.
+        /// </summary>
+        public static readonly StyledProperty<PenLineJoin> BorderLineJoinProperty =
+            AvaloniaProperty.Register<Border, PenLineJoin>(nameof(BorderLineJoin), PenLineJoin.Miter);
+
         private readonly BorderRenderHelper _borderRenderHelper = new BorderRenderHelper();
 
         /// <summary>
@@ -54,6 +80,10 @@ namespace Avalonia.Controls
                 BorderBrushProperty,
                 BorderThicknessProperty,
                 CornerRadiusProperty,
+                BorderDashArrayProperty,
+                BorderLineCapProperty,
+                BorderLineJoinProperty,
+                BorderDashOffsetProperty,
                 BoxShadowProperty);
             AffectsMeasure<Border>(BorderThicknessProperty);
         }
@@ -76,6 +106,15 @@ namespace Avalonia.Controls
             set { SetValue(BorderBrushProperty, value); }
         }
 
+        /// <summary>
+        /// Gets or sets a collection of <see cref="double"/> values that indicate the pattern of dashes and gaps that is used to outline shapes.
+        /// </summary>
+        public AvaloniaList<double>? BorderDashArray
+        {
+            get { return GetValue(BorderDashArrayProperty); }
+            set { SetValue(BorderDashArrayProperty, value); }
+        }
+
         /// <summary>
         /// Gets or sets the thickness of the border.
         /// </summary>
@@ -85,6 +124,33 @@ namespace Avalonia.Controls
             set { SetValue(BorderThicknessProperty, value); }
         }
 
+        /// <summary>
+        /// Gets or sets a value that specifies the distance within the dash pattern where a dash begins.
+        /// </summary>
+        public double BorderDashOffset
+        {
+            get { return GetValue(BorderDashOffsetProperty); }
+            set { SetValue(BorderDashOffsetProperty, value); }
+        }
+
+        /// <summary>
+        /// Gets or sets a <see cref="PenLineCap"/> enumeration value that describes the shape at the ends of a line.
+        /// </summary>
+        public PenLineCap BorderLineCap
+        {
+            get { return GetValue(BorderLineCapProperty); }
+            set { SetValue(BorderLineCapProperty, value); }
+        }
+
+        /// <summary>
+        /// Gets or sets a <see cref="PenLineJoin"/> enumeration value that specifies the type of join that is used at the vertices of a Shape.
+        /// </summary>
+        public PenLineJoin BorderLineJoin
+        {
+            get { return GetValue(BorderLineJoinProperty); }
+            set { SetValue(BorderLineJoinProperty, value); }
+        }
+
         /// <summary>
         /// Gets or sets the radius of the border rounded corners.
         /// </summary>
@@ -93,7 +159,7 @@ namespace Avalonia.Controls
             get { return GetValue(CornerRadiusProperty); }
             set { SetValue(CornerRadiusProperty, value); }
         }
-        
+
         /// <summary>
         /// Gets or sets the box shadow effect parameters
         /// </summary>
@@ -102,7 +168,7 @@ namespace Avalonia.Controls
             get => GetValue(BoxShadowProperty);
             set => SetValue(BoxShadowProperty, value);
         }
-        
+
         /// <summary>
         /// Renders the control.
         /// </summary>
@@ -110,7 +176,7 @@ namespace Avalonia.Controls
         public override void Render(DrawingContext context)
         {
             _borderRenderHelper.Render(context, Bounds.Size, BorderThickness, CornerRadius, Background, BorderBrush,
-                BoxShadow);
+                BoxShadow, BorderDashOffset, BorderLineCap, BorderLineJoin, BorderDashArray);
         }
 
         /// <summary>
diff --git a/src/Avalonia.Controls/Platform/ISystemDialogImpl.cs b/src/Avalonia.Controls/Platform/ISystemDialogImpl.cs
index affec6301b..7bd13ecdb1 100644
--- a/src/Avalonia.Controls/Platform/ISystemDialogImpl.cs
+++ b/src/Avalonia.Controls/Platform/ISystemDialogImpl.cs
@@ -1,5 +1,7 @@
 using System.Threading.Tasks;
 
+#nullable enable
+
 namespace Avalonia.Controls.Platform
 {
     /// <summary>
@@ -13,8 +15,8 @@ namespace Avalonia.Controls.Platform
         /// <param name="dialog">The details of the file dialog to show.</param>
         /// <param name="parent">The parent window.</param>
         /// <returns>A task returning the selected filenames.</returns>
-        Task<string[]> ShowFileDialogAsync(FileDialog dialog, Window parent);
+        Task<string[]?> ShowFileDialogAsync(FileDialog dialog, Window parent);
 
-        Task<string> ShowFolderDialogAsync(OpenFolderDialog dialog, Window parent);
+        Task<string?> ShowFolderDialogAsync(OpenFolderDialog dialog, Window parent);
     }
 }
diff --git a/src/Avalonia.Controls/TextBox.cs b/src/Avalonia.Controls/TextBox.cs
index 0a29db555c..00fc6002d1 100644
--- a/src/Avalonia.Controls/TextBox.cs
+++ b/src/Avalonia.Controls/TextBox.cs
@@ -642,15 +642,31 @@ namespace Avalonia.Controls
 
             if (!string.IsNullOrEmpty(input))
             {
-                DeleteSelection();
-                caretIndex = CaretIndex;
-                text = Text ?? string.Empty;
-                SetTextInternal(text.Substring(0, caretIndex) + input + text.Substring(caretIndex));
-                CaretIndex += input.Length;
-                ClearSelection();
-                if (IsUndoEnabled)
+                var oldText = _text;
+
+                _ignoreTextChanges = true;
+
+                try
                 {
-                    _undoRedoHelper.DiscardRedo();
+                    DeleteSelection(false);
+                    caretIndex = CaretIndex;
+                    text = Text ?? string.Empty;
+                    SetTextInternal(text.Substring(0, caretIndex) + input + text.Substring(caretIndex));
+                    CaretIndex += input.Length;
+                    ClearSelection();
+                    if (IsUndoEnabled)
+                    {
+                        _undoRedoHelper.DiscardRedo();
+                    }
+
+                    if (_text != oldText)
+                    {
+                        RaisePropertyChanged(TextProperty, oldText, _text);
+                    }
+                }
+                finally
+                {
+                    _ignoreTextChanges = false;
                 }
             }
         }
@@ -1285,7 +1301,7 @@ namespace Avalonia.Controls
             CaretIndex = SelectionEnd;
         }
 
-        private bool DeleteSelection()
+        private bool DeleteSelection(bool raiseTextChanged = true)
         {
             if (!IsReadOnly)
             {
@@ -1297,7 +1313,7 @@ namespace Avalonia.Controls
                     var start = Math.Min(selectionStart, selectionEnd);
                     var end = Math.Max(selectionStart, selectionEnd);
                     var text = Text;
-                    SetTextInternal(text.Substring(0, start) + text.Substring(end));
+                    SetTextInternal(text.Substring(0, start) + text.Substring(end), raiseTextChanged);
                     CaretIndex = start;
                     ClearSelection();
                     return true;
@@ -1348,16 +1364,23 @@ namespace Avalonia.Controls
             return i;
         }
 
-        private void SetTextInternal(string value)
+        private void SetTextInternal(string value, bool raiseTextChanged = true)
         {
-            try
+            if (raiseTextChanged)
             {
-                _ignoreTextChanges = true;
-                SetAndRaise(TextProperty, ref _text, value);
+                try
+                {
+                    _ignoreTextChanges = true;
+                    SetAndRaise(TextProperty, ref _text, value);
+                }
+                finally
+                {
+                    _ignoreTextChanges = false;
+                }
             }
-            finally
+            else
             {
-                _ignoreTextChanges = false;
+                _text = value;
             }
         }
 
diff --git a/src/Avalonia.Controls/Utils/BorderRenderHelper.cs b/src/Avalonia.Controls/Utils/BorderRenderHelper.cs
index f8ab58d46e..bae787f0ed 100644
--- a/src/Avalonia.Controls/Utils/BorderRenderHelper.cs
+++ b/src/Avalonia.Controls/Utils/BorderRenderHelper.cs
@@ -1,8 +1,10 @@
 using System;
+using Avalonia.Collections;
 using Avalonia.Media;
 using Avalonia.Media.Immutable;
 using Avalonia.Platform;
 using Avalonia.Utilities;
+using JetBrains.Annotations;
 
 namespace Avalonia.Controls.Utils
 {
@@ -15,8 +17,13 @@ namespace Avalonia.Controls.Utils
         private Size _size;
         private Thickness _borderThickness;
         private CornerRadius _cornerRadius;
+        private AvaloniaList<double> _borderDashArray;
+        private double _borderDashOffset;
+        private PenLineCap _borderLineCap;
+        private PenLineJoin _borderJoin;
         private bool _initialized;
 
+
         void Update(Size finalSize, Thickness borderThickness, CornerRadius cornerRadius)
         {
             _backendSupportsIndividualCorners ??= AvaloniaLocator.Current.GetService<IPlatformRenderInterface>()
@@ -60,7 +67,8 @@ namespace Avalonia.Controls.Utils
 
                 if (boundRect.Width != 0 && innerRect.Height != 0)
                 {
-                    var borderGeometryKeypoints = new BorderGeometryKeypoints(boundRect, borderThickness, cornerRadius, false);
+                    var borderGeometryKeypoints =
+                        new BorderGeometryKeypoints(boundRect, borderThickness, cornerRadius, false);
                     var borderGeometry = new StreamGeometry();
 
                     using (var ctx = borderGeometry.Open())
@@ -84,17 +92,22 @@ namespace Avalonia.Controls.Utils
 
         public void Render(DrawingContext context,
             Size finalSize, Thickness borderThickness, CornerRadius cornerRadius,
-            IBrush background, IBrush borderBrush, BoxShadows boxShadows)
+            IBrush background, IBrush borderBrush, BoxShadows boxShadows, double borderDashOffset = 0,
+            PenLineCap borderLineCap = PenLineCap.Flat, PenLineJoin borderLineJoin = PenLineJoin.Miter,
+            AvaloniaList<double> borderDashArray = null)
         {
             if (_size != finalSize
                 || _borderThickness != borderThickness
                 || _cornerRadius != cornerRadius
                 || !_initialized)
                 Update(finalSize, borderThickness, cornerRadius);
-            RenderCore(context, background, borderBrush, boxShadows);
+            RenderCore(context, background, borderBrush, boxShadows, borderDashOffset, borderLineCap, borderLineJoin,
+                borderDashArray);
         }
 
-        void RenderCore(DrawingContext context, IBrush background, IBrush borderBrush, BoxShadows boxShadows)
+        void RenderCore(DrawingContext context, IBrush background, IBrush borderBrush, BoxShadows boxShadows,
+            double borderDashOffset, PenLineCap borderLineCap, PenLineJoin borderLineJoin,
+            AvaloniaList<double> borderDashArray)
         {
             if (_useComplexRendering)
             {
@@ -115,11 +128,25 @@ namespace Avalonia.Controls.Utils
                 var borderThickness = _borderThickness.Top;
                 IPen pen = null;
 
+
+                ImmutableDashStyle? dashStyle = null;
+
+                if (borderDashArray != null && borderDashArray.Count > 0)
+                {
+                    dashStyle = new ImmutableDashStyle(borderDashArray, borderDashOffset);
+                }
+
                 if (borderBrush != null && borderThickness > 0)
                 {
-                    pen = new ImmutablePen(borderBrush.ToImmutable(), borderThickness);
+                    pen = new ImmutablePen(
+                        borderBrush.ToImmutable(),
+                        borderThickness,
+                        dashStyle,
+                        borderLineCap,
+                        borderLineJoin);
                 }
 
+
                 var rect = new Rect(_size);
                 if (!MathUtilities.IsZero(borderThickness))
                     rect = rect.Deflate(borderThickness * 0.5);
@@ -130,7 +157,8 @@ namespace Avalonia.Controls.Utils
             }
         }
 
-        private static void CreateGeometry(StreamGeometryContext context, Rect boundRect, BorderGeometryKeypoints keypoints)
+        private static void CreateGeometry(StreamGeometryContext context, Rect boundRect,
+            BorderGeometryKeypoints keypoints)
         {
             context.BeginFigure(keypoints.TopLeft, true);
 
@@ -184,7 +212,8 @@ namespace Avalonia.Controls.Utils
 
         private class BorderGeometryKeypoints
         {
-            internal BorderGeometryKeypoints(Rect boundRect, Thickness borderThickness, CornerRadius cornerRadius, bool inner)
+            internal BorderGeometryKeypoints(Rect boundRect, Thickness borderThickness, CornerRadius cornerRadius,
+                bool inner)
             {
                 var left = 0.5 * borderThickness.Left;
                 var top = 0.5 * borderThickness.Top;
@@ -206,10 +235,13 @@ namespace Avalonia.Controls.Utils
                     topLeftX = Math.Max(0, cornerRadius.TopLeft - left) + boundRect.TopLeft.X;
                     topRightX = boundRect.Width - Math.Max(0, cornerRadius.TopRight - top) + boundRect.TopLeft.X;
                     rightTopY = Math.Max(0, cornerRadius.TopRight - right) + boundRect.TopLeft.Y;
-                    rightBottomY = boundRect.Height - Math.Max(0, cornerRadius.BottomRight - bottom) + boundRect.TopLeft.Y;
-                    bottomRightX = boundRect.Width - Math.Max(0, cornerRadius.BottomRight - right) + boundRect.TopLeft.X;
+                    rightBottomY = boundRect.Height - Math.Max(0, cornerRadius.BottomRight - bottom) +
+                                   boundRect.TopLeft.Y;
+                    bottomRightX = boundRect.Width - Math.Max(0, cornerRadius.BottomRight - right) +
+                                   boundRect.TopLeft.X;
                     bottomLeftX = Math.Max(0, cornerRadius.BottomLeft - left) + boundRect.TopLeft.X;
-                    leftBottomY = boundRect.Height - Math.Max(0, cornerRadius.BottomLeft - bottom) + boundRect.TopLeft.Y;
+                    leftBottomY = boundRect.Height - Math.Max(0, cornerRadius.BottomLeft - bottom) +
+                                  boundRect.TopLeft.Y;
                 }
                 else
                 {
diff --git a/src/Avalonia.Styling/Controls/ResourceDictionary.cs b/src/Avalonia.Styling/Controls/ResourceDictionary.cs
index c56dd74143..e797f8cf8b 100644
--- a/src/Avalonia.Styling/Controls/ResourceDictionary.cs
+++ b/src/Avalonia.Styling/Controls/ResourceDictionary.cs
@@ -68,7 +68,8 @@ namespace Avalonia.Controls
                             {
                                 x.RemoveOwner(Owner);
                             }
-                        }, null);
+                        }, 
+                        () => throw new NotSupportedException("Dictionary reset not supported"));
                 }
 
                 return _mergedDictionaries;
diff --git a/src/Windows/Avalonia.Win32.Interop/Avalonia.Win32.Interop.csproj b/src/Windows/Avalonia.Win32.Interop/Avalonia.Win32.Interop.csproj
index 0e11ee3b92..9f49808422 100644
--- a/src/Windows/Avalonia.Win32.Interop/Avalonia.Win32.Interop.csproj
+++ b/src/Windows/Avalonia.Win32.Interop/Avalonia.Win32.Interop.csproj
@@ -1,8 +1,9 @@
-<Project Sdk="MSBuild.Sdk.Extras">
+<Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <TargetFramework>net461</TargetFramework>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <UseWpf>true</UseWpf>
+    <UseWindowsForms>true</UseWindowsForms>
     <ExtrasEnableImplicitWinFormsReferences>true</ExtrasEnableImplicitWinFormsReferences>
     <UseDirect3D9>true</UseDirect3D9>
     <PackageId>Avalonia.Win32.Interoperability</PackageId>
diff --git a/src/Windows/Avalonia.Win32/Avalonia.Win32.csproj b/src/Windows/Avalonia.Win32/Avalonia.Win32.csproj
index fe5f806fbe..2a2aff322a 100644
--- a/src/Windows/Avalonia.Win32/Avalonia.Win32.csproj
+++ b/src/Windows/Avalonia.Win32/Avalonia.Win32.csproj
@@ -9,6 +9,7 @@
     <ProjectReference Include="..\..\..\packages\Avalonia\Avalonia.csproj" />
     <PackageReference Include="Avalonia.Angle.Windows.Natives" Version="2.1.0.2020091801" />
     <AvnComIdl Include="WinRT\winrt.idl" OutputFile="WinRT\WinRT.Generated.cs" />
+    <AvnComIdl Include="Win32Com\win32.idl" OutputFile="Win32Com\Win32.Generated.cs" />
   </ItemGroup>
   <Import Project="../../../build/MicroCom.targets" />
   <Import Project="$(MSBuildThisFileDirectory)\..\..\..\build\System.Drawing.Common.props" />    
diff --git a/src/Windows/Avalonia.Win32/Interop/UnmanagedMethods.cs b/src/Windows/Avalonia.Win32/Interop/UnmanagedMethods.cs
index 938f4222e0..648a3c6a34 100644
--- a/src/Windows/Avalonia.Win32/Interop/UnmanagedMethods.cs
+++ b/src/Windows/Avalonia.Win32/Interop/UnmanagedMethods.cs
@@ -6,6 +6,9 @@ using System.Runtime.InteropServices;
 using System.Runtime.InteropServices.ComTypes;
 using System.Text;
 
+using Avalonia.MicroCom;
+using Avalonia.Win32.Win32Com;
+
 // ReSharper disable InconsistentNaming
 #pragma warning disable 169, 649
 
@@ -1244,8 +1247,19 @@ namespace Avalonia.Win32.Interop
         internal static extern int CoCreateInstance(ref Guid clsid,
             IntPtr ignore1, int ignore2, ref Guid iid, [Out] out IntPtr pUnkOuter);
 
+        internal unsafe static T CreateInstance<T>(ref Guid clsid, ref Guid iid) where T : IUnknown
+        {
+            var hresult = CoCreateInstance(ref clsid, IntPtr.Zero, 1, ref iid, out IntPtr pUnk);
+            if (hresult != 0)
+            {
+                throw new COMException("CreateInstance", hresult);
+            }
+            using var unk = MicroComRuntime.CreateProxyFor<IUnknown>(pUnk, true);
+            return MicroComRuntime.QueryInterface<T>(unk);
+        }
+
         [DllImport("shell32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
-        internal static extern int SHCreateItemFromParsingName([MarshalAs(UnmanagedType.LPWStr)] string pszPath, IntPtr pbc, ref Guid riid, [MarshalAs(UnmanagedType.Interface)] out IShellItem ppv);
+        internal static extern int SHCreateItemFromParsingName([MarshalAs(UnmanagedType.LPWStr)] string pszPath, IntPtr pbc, ref Guid riid, out IntPtr ppv);
 
         [DllImport("user32.dll", SetLastError = true)]
         public static extern bool OpenClipboard(IntPtr hWndOwner);
@@ -1888,7 +1902,8 @@ namespace Avalonia.Win32.Interop
             E_INVALIDARG = 0x80070057,
             E_OUTOFMEMORY = 0x8007000E,
             E_NOTIMPL = 0x80004001,
-            E_UNEXPECTED = 0x8000FFFF
+            E_UNEXPECTED = 0x8000FFFF,
+            E_CANCELLED = 0x800704C7,
         }
 
         public enum Icons
@@ -1897,33 +1912,6 @@ namespace Avalonia.Win32.Interop
             ICON_BIG = 1
         }
 
-        public const uint SIGDN_FILESYSPATH = 0x80058000;
-
-        [Flags]
-        public enum FOS : uint
-        {
-            FOS_OVERWRITEPROMPT = 0x00000002,
-            FOS_STRICTFILETYPES = 0x00000004,
-            FOS_NOCHANGEDIR = 0x00000008,
-            FOS_PICKFOLDERS = 0x00000020,
-            FOS_FORCEFILESYSTEM = 0x00000040, // Ensure that items returned are filesystem items.
-            FOS_ALLNONSTORAGEITEMS = 0x00000080, // Allow choosing items that have no storage.
-            FOS_NOVALIDATE = 0x00000100,
-            FOS_ALLOWMULTISELECT = 0x00000200,
-            FOS_PATHMUSTEXIST = 0x00000800,
-            FOS_FILEMUSTEXIST = 0x00001000,
-            FOS_CREATEPROMPT = 0x00002000,
-            FOS_SHAREAWARE = 0x00004000,
-            FOS_NOREADONLYRETURN = 0x00008000,
-            FOS_NOTESTFILECREATE = 0x00010000,
-            FOS_HIDEMRUPLACES = 0x00020000,
-            FOS_HIDEPINNEDPLACES = 0x00040000,
-            FOS_NODEREFERENCELINKS = 0x00100000,
-            FOS_DONTADDTORECENT = 0x02000000,
-            FOS_FORCESHOWHIDDEN = 0x10000000,
-            FOS_DEFAULTNOMINIMODE = 0x20000000
-        }
-
         public static class ShellIds
         {
             public static readonly Guid OpenFileDialog = Guid.Parse("DC1C5A9C-E88A-4DDE-A5A1-60F82A20AEF7");
@@ -1934,228 +1922,6 @@ namespace Avalonia.Win32.Interop
             public static readonly Guid ITaskBarList2 = Guid.Parse("ea1afb91-9e28-4b86-90e9-9e9f8a5eefaf");
         }
 
-        [ComImport(), Guid("42F85136-DB7E-439C-85F1-E4075D135FC8"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
-        public interface IFileDialog
-        {
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            [PreserveSig()]
-            uint Show([In, Optional] IntPtr hwndOwner); //IModalWindow
-
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint SetFileTypes(uint cFileTypes, [In, MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 0)] COMDLG_FILTERSPEC[] rgFilterSpec);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint SetFileTypeIndex([In] uint iFileType);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint GetFileTypeIndex(out uint piFileType);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint Advise([In, MarshalAs(UnmanagedType.Interface)] IntPtr pfde, out uint pdwCookie);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint Unadvise([In] uint dwCookie);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint SetOptions([In] uint fos);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint GetOptions(out uint fos);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void SetDefaultFolder([In, MarshalAs(UnmanagedType.Interface)] IShellItem psi);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint SetFolder([In, MarshalAs(UnmanagedType.Interface)] IShellItem psi);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint GetFolder([MarshalAs(UnmanagedType.Interface)] out IShellItem ppsi);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint GetCurrentSelection([MarshalAs(UnmanagedType.Interface)] out IShellItem ppsi);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint SetFileName([In, MarshalAs(UnmanagedType.LPWStr)] string pszName);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint GetFileName([MarshalAs(UnmanagedType.LPWStr)] out string pszName);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint SetTitle([In, MarshalAs(UnmanagedType.LPWStr)] string pszTitle);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint SetOkButtonLabel([In, MarshalAs(UnmanagedType.LPWStr)] string pszText);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint SetFileNameLabel([In, MarshalAs(UnmanagedType.LPWStr)] string pszLabel);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint GetResult([MarshalAs(UnmanagedType.Interface)] out IShellItem ppsi);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint AddPlace([In, MarshalAs(UnmanagedType.Interface)] IShellItem psi, uint fdap);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint SetDefaultExtension([In, MarshalAs(UnmanagedType.LPWStr)] string pszDefaultExtension);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint Close([MarshalAs(UnmanagedType.Error)] uint hr);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint SetClientGuid([In] ref Guid guid);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint ClearClientData();
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint SetFilter([MarshalAs(UnmanagedType.Interface)] IntPtr pFilter);
-
-        }
-
-        [ComImport, Guid("d57c7288-d4ad-4768-be02-9d969532d960"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
-        public interface IFileOpenDialog
-        {
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            [PreserveSig()]
-            uint Show([In, Optional] IntPtr hwndOwner); //IModalWindow 
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint SetFileTypes([In] uint cFileTypes, [In, MarshalAs(UnmanagedType.LPArray)] IntPtr rgFilterSpec);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void SetFileTypeIndex([In] uint iFileType);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void GetFileTypeIndex(out uint piFileType);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint Advise([In, MarshalAs(UnmanagedType.Interface)] IntPtr pfde, out uint pdwCookie);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void Unadvise([In] uint dwCookie);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint SetOptions([In] uint fos);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint GetOptions(out uint fos);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void SetDefaultFolder([In, MarshalAs(UnmanagedType.Interface)] IShellItem psi);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void SetFolder([In, MarshalAs(UnmanagedType.Interface)] IShellItem psi);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void GetFolder([MarshalAs(UnmanagedType.Interface)] out IShellItem ppsi);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void GetCurrentSelection([MarshalAs(UnmanagedType.Interface)] out IShellItem ppsi);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void SetFileName([In, MarshalAs(UnmanagedType.LPWStr)] string pszName);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void GetFileName([MarshalAs(UnmanagedType.LPWStr)] out string pszName);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void SetTitle([In, MarshalAs(UnmanagedType.LPWStr)] string pszTitle);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void SetOkButtonLabel([In, MarshalAs(UnmanagedType.LPWStr)] string pszText);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void SetFileNameLabel([In, MarshalAs(UnmanagedType.LPWStr)] string pszLabel);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void GetResult([MarshalAs(UnmanagedType.Interface)] out IShellItem ppsi);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint AddPlace([In, MarshalAs(UnmanagedType.Interface)] IShellItem psi, uint fdap);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void SetDefaultExtension([In, MarshalAs(UnmanagedType.LPWStr)] string pszDefaultExtension);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void Close([MarshalAs(UnmanagedType.Error)] int hr);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void SetClientGuid([In] ref Guid guid);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void ClearClientData();
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void SetFilter([MarshalAs(UnmanagedType.Interface)] IntPtr pFilter);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void GetResults([MarshalAs(UnmanagedType.Interface)] out IShellItemArray ppenum);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void GetSelectedItems([MarshalAs(UnmanagedType.Interface)] out IShellItemArray ppsai);
-        }
-
-        [ComImport, Guid("B63EA76D-1F85-456F-A19C-48159EFA858B"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
-        public interface IShellItemArray
-        {
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void BindToHandler([In, MarshalAs(UnmanagedType.Interface)] IntPtr pbc, [In] ref Guid rbhid,
-                         [In] ref Guid riid, out IntPtr ppvOut);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void GetPropertyStore([In] int Flags, [In] ref Guid riid, out IntPtr ppv);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void GetPropertyDescriptionList([In] ref PROPERTYKEY keyType, [In] ref Guid riid, out IntPtr ppv);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void GetAttributes([In] SIATTRIBFLAGS dwAttribFlags, [In] uint sfgaoMask, out uint psfgaoAttribs);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void GetCount(out uint pdwNumItems);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void GetItemAt([In] uint dwIndex, [MarshalAs(UnmanagedType.Interface)] out IShellItem ppsi);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            void EnumItems([MarshalAs(UnmanagedType.Interface)] out IntPtr ppenumShellItems);
-        }
-
-        [StructLayout(LayoutKind.Sequential, Pack = 4)]
-        public struct PROPERTYKEY
-        {
-            public Guid fmtid;
-            public uint pid;
-        }
-
-        public enum SIATTRIBFLAGS
-        {
-            SIATTRIBFLAGS_AND = 1,
-            SIATTRIBFLAGS_APPCOMPAT = 3,
-            SIATTRIBFLAGS_OR = 2
-        }
-
-        [ComImport, Guid("43826D1E-E718-42EE-BC55-A1E261C37BFE"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
-        public interface IShellItem
-        {
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint BindToHandler([In] IntPtr pbc, [In] ref Guid rbhid, [In] ref Guid riid, [Out, MarshalAs(UnmanagedType.Interface)] out IntPtr ppvOut);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint GetParent([MarshalAs(UnmanagedType.Interface)] out IShellItem ppsi);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint GetDisplayName([In] uint sigdnName, out IntPtr ppszName);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint GetAttributes([In] uint sfgaoMask, out uint psfgaoAttribs);
-
-            [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
-            uint Compare([In, MarshalAs(UnmanagedType.Interface)] IShellItem psi, [In] uint hint, out int piOrder);
-
-        }
-
         [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
         public struct COMDLG_FILTERSPEC
         {
diff --git a/src/Windows/Avalonia.Win32/SystemDialogImpl.cs b/src/Windows/Avalonia.Win32/SystemDialogImpl.cs
index f595a58c91..29844368db 100644
--- a/src/Windows/Avalonia.Win32/SystemDialogImpl.cs
+++ b/src/Windows/Avalonia.Win32/SystemDialogImpl.cs
@@ -1,170 +1,229 @@
+#nullable enable
 using System;
 using System.Collections.Generic;
+using System.ComponentModel;
 using System.Linq;
 using System.Runtime.InteropServices;
 using System.Threading.Tasks;
 using Avalonia.Controls;
 using Avalonia.Controls.Platform;
+using Avalonia.MicroCom;
 using Avalonia.Win32.Interop;
+using Avalonia.Win32.Win32Com;
 
 namespace Avalonia.Win32
 {
-    class SystemDialogImpl : ISystemDialogImpl
+    internal class SystemDialogImpl : ISystemDialogImpl
     {
-        private const UnmanagedMethods.FOS DefaultDialogOptions = UnmanagedMethods.FOS.FOS_FORCEFILESYSTEM | UnmanagedMethods.FOS.FOS_NOVALIDATE |
-            UnmanagedMethods.FOS.FOS_NOTESTFILECREATE | UnmanagedMethods.FOS.FOS_DONTADDTORECENT;
+        private const uint SIGDN_FILESYSPATH = 0x80058000;
 
-        public unsafe Task<string[]> ShowFileDialogAsync(FileDialog dialog, Window parent)
+        private const FILEOPENDIALOGOPTIONS DefaultDialogOptions = FILEOPENDIALOGOPTIONS.FOS_FORCEFILESYSTEM | FILEOPENDIALOGOPTIONS.FOS_NOVALIDATE |
+            FILEOPENDIALOGOPTIONS.FOS_NOTESTFILECREATE | FILEOPENDIALOGOPTIONS.FOS_DONTADDTORECENT;
+
+        public unsafe Task<string[]?> ShowFileDialogAsync(FileDialog dialog, Window parent)
         {
             var hWnd = parent?.PlatformImpl?.Handle?.Handle ?? IntPtr.Zero;
-            return Task.Factory.StartNew(() =>
+            return Task.Run(() =>
             {
-                string[] result = default;
-
-                Guid clsid = dialog is OpenFileDialog ? UnmanagedMethods.ShellIds.OpenFileDialog : UnmanagedMethods.ShellIds.SaveFileDialog;
-                Guid iid = UnmanagedMethods.ShellIds.IFileDialog;
-                UnmanagedMethods.CoCreateInstance(ref clsid, IntPtr.Zero, 1, ref iid, out object unk);
-                var frm = (UnmanagedMethods.IFileDialog)unk;
+                string[]? result = default;
+                try
+                {
+                    var clsid = dialog is OpenFileDialog ? UnmanagedMethods.ShellIds.OpenFileDialog : UnmanagedMethods.ShellIds.SaveFileDialog;
+                    var iid = UnmanagedMethods.ShellIds.IFileDialog;
+                    var frm = UnmanagedMethods.CreateInstance<IFileDialog>(ref clsid, ref iid);
 
-                var openDialog = dialog as OpenFileDialog;
+                    var openDialog = dialog as OpenFileDialog;
 
-                uint options;
-                frm.GetOptions(out options);
-                options |= (uint)(DefaultDialogOptions);
-                if (openDialog?.AllowMultiple == true)
-                    options |= (uint)UnmanagedMethods.FOS.FOS_ALLOWMULTISELECT;
-                frm.SetOptions(options);
+                    var options = frm.Options;
+                    options |= DefaultDialogOptions;
+                    if (openDialog?.AllowMultiple == true)
+                    {
+                        options |= FILEOPENDIALOGOPTIONS.FOS_ALLOWMULTISELECT;
+                    }
+                    frm.SetOptions(options);
 
-                var defaultExtension = (dialog as SaveFileDialog)?.DefaultExtension ?? "";
-                frm.SetDefaultExtension(defaultExtension);
-                frm.SetFileName(dialog.InitialFileName ?? "");
-                frm.SetTitle(dialog.Title ?? "");
+                    var defaultExtension = (dialog as SaveFileDialog)?.DefaultExtension ?? "";
+                    fixed (char* pExt = defaultExtension)
+                    {
+                        frm.SetDefaultExtension(pExt);
+                    }
 
-                var filters = new List<UnmanagedMethods.COMDLG_FILTERSPEC>();
-                if (dialog.Filters != null)
-                {
-                    foreach (var filter in dialog.Filters)
+                    var initialFileName = dialog.InitialFileName ?? "";
+                    fixed (char* fExt = initialFileName)
                     {
-                        var extMask = string.Join(";", filter.Extensions.Select(e => "*." + e));
-                        filters.Add(new UnmanagedMethods.COMDLG_FILTERSPEC { pszName = filter.Name, pszSpec = extMask });
+                        frm.SetFileName(fExt);
                     }
-                }
-                if (filters.Count == 0)
-                    filters.Add(new UnmanagedMethods.COMDLG_FILTERSPEC { pszName = "All files", pszSpec = "*.*" });
 
-                frm.SetFileTypes((uint)filters.Count, filters.ToArray());
-                frm.SetFileTypeIndex(0);
+                    var title = dialog.Title ?? "";
+                    fixed (char* tExt = title)
+                    {
+                        frm.SetTitle(tExt);
+                    }
 
-                if (dialog.Directory != null)
-                {
-                    UnmanagedMethods.IShellItem directoryShellItem;
-                    Guid riid = UnmanagedMethods.ShellIds.IShellItem;
-                    if (UnmanagedMethods.SHCreateItemFromParsingName(dialog.Directory, IntPtr.Zero, ref riid, out directoryShellItem) == (uint)UnmanagedMethods.HRESULT.S_OK)
+                    fixed (void* pFilters = FiltersToPointer(dialog.Filters, out var count))
                     {
-                        frm.SetFolder(directoryShellItem);
-                        frm.SetDefaultFolder(directoryShellItem);
+                        frm.SetFileTypes((ushort)count, pFilters);
                     }
-                }
 
-                if (frm.Show(hWnd) == (uint)UnmanagedMethods.HRESULT.S_OK)
-                {
-                    if (openDialog?.AllowMultiple == true)
+                    frm.SetFileTypeIndex(0);
+
+                    if (dialog.Directory != null)
                     {
-                        UnmanagedMethods.IShellItemArray shellItemArray;
-                        ((UnmanagedMethods.IFileOpenDialog)frm).GetResults(out shellItemArray);
-                        uint count;
-                        shellItemArray.GetCount(out count);
-                        result = new string[count];
-                        for (uint i = 0; i < count; i++)
+                        var riid = UnmanagedMethods.ShellIds.IShellItem;
+                        if (UnmanagedMethods.SHCreateItemFromParsingName(dialog.Directory, IntPtr.Zero, ref riid, out var directoryShellItem)
+                            == (uint)UnmanagedMethods.HRESULT.S_OK)
                         {
-                            UnmanagedMethods.IShellItem shellItem;
-                            shellItemArray.GetItemAt(i, out shellItem);
-                            result[i] = GetAbsoluteFilePath(shellItem);
+                            var proxy = MicroComRuntime.CreateProxyFor<IShellItem>(directoryShellItem, true);
+                            frm.SetFolder(proxy);
+                            frm.SetDefaultFolder(proxy);
                         }
                     }
-                    else
+
+                    frm.Show(hWnd);
+
+                    if (openDialog?.AllowMultiple == true)
                     {
-                        UnmanagedMethods.IShellItem shellItem;
-                        if (frm.GetResult(out shellItem) == (uint)UnmanagedMethods.HRESULT.S_OK)
+                        using var fileOpenDialog = frm.QueryInterface<IFileOpenDialog>();
+                        var shellItemArray = fileOpenDialog.Results;
+                        var count = shellItemArray.Count;
+
+                        var results = new List<string>();
+                        for (int i = 0; i < count; i++)
                         {
-                            result = new string[] { GetAbsoluteFilePath(shellItem) };
+                            var shellItem = shellItemArray.GetItemAt(i);
+                            if (GetAbsoluteFilePath(shellItem) is { } selected)
+                            {
+                                results.Add(selected);
+                            }
                         }
+                        result = results.ToArray();
+                    }
+                    else if (frm.Result is { } shellItem
+                        && GetAbsoluteFilePath(shellItem) is { } singleResult)
+                    {
+                        result = new[] { singleResult };
                     }
-                }
 
-                return result;
-            });
+                    return result;
+                }
+                catch (COMException ex)
+                {
+                    if ((uint)ex.HResult == (uint)UnmanagedMethods.HRESULT.E_CANCELLED)
+                    {
+                        return result;
+                    }
+                    throw new Win32Exception(ex.HResult);
+                }
+            })!;
         }
 
-        public Task<string> ShowFolderDialogAsync(OpenFolderDialog dialog, Window parent)
+        public unsafe Task<string?> ShowFolderDialogAsync(OpenFolderDialog dialog, Window parent)
         {
-            return Task.Factory.StartNew(() =>
+            return Task.Run(() =>
             {
-                string result = default;
+                string? result = default;
+                try
+                {
+                    var hWnd = parent?.PlatformImpl?.Handle?.Handle ?? IntPtr.Zero;
+                    var clsid = UnmanagedMethods.ShellIds.OpenFileDialog;
+                    var iid = UnmanagedMethods.ShellIds.IFileDialog;
+                    var frm = UnmanagedMethods.CreateInstance<IFileDialog>(ref clsid, ref iid);
 
-                var hWnd = parent?.PlatformImpl?.Handle?.Handle ?? IntPtr.Zero;
-                Guid clsid = UnmanagedMethods.ShellIds.OpenFileDialog;
-                Guid iid = UnmanagedMethods.ShellIds.IFileDialog;
+                    var options = frm.Options;
+                    options = FILEOPENDIALOGOPTIONS.FOS_PICKFOLDERS | DefaultDialogOptions;
+                    frm.SetOptions(options);
 
-                UnmanagedMethods.CoCreateInstance(ref clsid, IntPtr.Zero, 1, ref iid, out object unk);
-                var frm = (UnmanagedMethods.IFileDialog)unk;
-                uint options;
-                frm.GetOptions(out options);
-                options |= (uint)(UnmanagedMethods.FOS.FOS_PICKFOLDERS | DefaultDialogOptions);
-                frm.SetOptions(options);
-                frm.SetTitle(dialog.Title ?? "");
+                    var title = dialog.Title ?? "";
+                    fixed (char* tExt = title)
+                    {
+                        frm.SetTitle(tExt);
+                    }
 
-                if (dialog.Directory != null)
-                {
-                    UnmanagedMethods.IShellItem directoryShellItem;
-                    Guid riid = UnmanagedMethods.ShellIds.IShellItem;
-                    if (UnmanagedMethods.SHCreateItemFromParsingName(dialog.Directory, IntPtr.Zero, ref riid, out directoryShellItem) == (uint)UnmanagedMethods.HRESULT.S_OK)
+                    if (dialog.Directory != null)
                     {
-                        frm.SetFolder(directoryShellItem);
+                        var riid = UnmanagedMethods.ShellIds.IShellItem;
+                        if (UnmanagedMethods.SHCreateItemFromParsingName(dialog.Directory, IntPtr.Zero, ref riid, out var directoryShellItem)
+                            == (uint)UnmanagedMethods.HRESULT.S_OK)
+                        {
+                            var proxy = MicroComRuntime.CreateProxyFor<IShellItem>(directoryShellItem, true);
+                            frm.SetFolder(proxy);
+                            frm.SetDefaultFolder(proxy);
+                        }
                     }
-                }
 
-                if (dialog.Directory != null)
-                {
-                    UnmanagedMethods.IShellItem directoryShellItem;
-                    Guid riid = UnmanagedMethods.ShellIds.IShellItem;
-                    if (UnmanagedMethods.SHCreateItemFromParsingName(dialog.Directory, IntPtr.Zero, ref riid, out directoryShellItem) == (uint)UnmanagedMethods.HRESULT.S_OK)
+                    frm.Show(hWnd);
+                    if (frm.Result is not null)
                     {
-                        frm.SetDefaultFolder(directoryShellItem);
+                        result = GetAbsoluteFilePath(frm.Result);
                     }
-                }
 
-                if (frm.Show(hWnd) == (uint)UnmanagedMethods.HRESULT.S_OK)
+                    return result;
+                }
+                catch (COMException ex)
                 {
-                    UnmanagedMethods.IShellItem shellItem;
-                    if (frm.GetResult(out shellItem) == (uint)UnmanagedMethods.HRESULT.S_OK)
+                    if ((uint)ex.HResult == (uint)UnmanagedMethods.HRESULT.E_CANCELLED)
                     {
-                        result = GetAbsoluteFilePath(shellItem);
+                        return result;
                     }
+                    throw new Win32Exception(ex.HResult);
                 }
-
-                return result;
             });
         }
 
-        private string GetAbsoluteFilePath(UnmanagedMethods.IShellItem shellItem)
+        private unsafe string? GetAbsoluteFilePath(IShellItem shellItem)
         {
-            IntPtr pszString;
-            if (shellItem.GetDisplayName(UnmanagedMethods.SIGDN_FILESYSPATH, out pszString) == (uint)UnmanagedMethods.HRESULT.S_OK)
+            var pszString = new IntPtr(shellItem.GetDisplayName(SIGDN_FILESYSPATH));
+            if (pszString != IntPtr.Zero)
             {
-                if (pszString != IntPtr.Zero)
+                try
                 {
-                    try
-                    {
-                        return Marshal.PtrToStringAuto(pszString);
-                    }
-                    finally
-                    {
-                        Marshal.FreeCoTaskMem(pszString);
-                    }
+                    return Marshal.PtrToStringUni(pszString);
+                }
+                finally
+                {
+                    Marshal.FreeCoTaskMem(pszString);
                 }
             }
             return default;
         }
+
+        private unsafe byte[] FiltersToPointer(List<FileDialogFilter>? filters, out int lenght)
+        {
+            if (filters == null || filters.Count == 0)
+            {
+                filters = new List<FileDialogFilter>
+                {
+                    new FileDialogFilter { Name = "All files", Extensions = new List<string> { "*" } }
+                };
+            }
+
+            var size = Marshal.SizeOf<UnmanagedMethods.COMDLG_FILTERSPEC>();
+            var arr = new byte[size];
+            var resultArr = new byte[size * filters.Count];
+
+            for (int i = 0; i < filters.Count; i++)
+            {
+                var filter = filters[i];
+                var filterPtr = Marshal.AllocHGlobal(size);
+                try
+                {
+                    var filterStr = new UnmanagedMethods.COMDLG_FILTERSPEC
+                    {
+                        pszName = filter.Name ?? string.Empty,
+                        pszSpec = string.Join(";", filter.Extensions.Select(e => "*." + e))
+                    };
+
+                    Marshal.StructureToPtr(filterStr, filterPtr, false);
+                    Marshal.Copy(filterPtr, resultArr, i * size, size);
+                }
+                finally
+                {
+                    Marshal.FreeHGlobal(filterPtr);
+                }
+            }
+
+            lenght = filters.Count;
+            return resultArr;
+        }
     }
 }
diff --git a/src/Windows/Avalonia.Win32/Win32Com/win32.idl b/src/Windows/Avalonia.Win32/Win32Com/win32.idl
new file mode 100644
index 0000000000..904ac41ff2
--- /dev/null
+++ b/src/Windows/Avalonia.Win32/Win32Com/win32.idl
@@ -0,0 +1,191 @@
+@clr-namespace Avalonia.Win32.Win32Com
+@clr-access internal
+@clr-map FLOAT float
+@clr-map HSTRING IntPtr
+@clr-map Vector2 System.Numerics.Vector2
+@clr-map Vector3 System.Numerics.Vector3
+@clr-map Quaternion System.Numerics.Quaternion
+@clr-map Matrix4x4 System.Numerics.Matrix4x4
+@clr-map RECT Avalonia.Win32.Interop.UnmanagedMethods.RECT
+@clr-map SIZE Avalonia.Win32.Interop.UnmanagedMethods.SIZE
+@clr-map POINT Avalonia.Win32.Interop.UnmanagedMethods.POINT
+@clr-map HWND IntPtr
+@clr-map BOOL int
+@clr-map DWORD int
+@clr-map boolean int
+@clr-map BYTE byte
+@clr-map INT16 short
+@clr-map INT32 int
+@clr-map INT64 long
+@clr-map UINT ushort
+@clr-map UINT16 ushort
+@clr-map ULONG uint
+@clr-map UINT32 uint
+@clr-map UINT64 ulong
+@clr-map DOUBLE double
+@clr-map GUID System.Guid
+@clr-map REFGUID System.Guid*
+@clr-map REFIID System.Guid*
+@clr-map WCHAR System.Char
+
+[flags]
+enum FILEOPENDIALOGOPTIONS
+{
+    FOS_OVERWRITEPROMPT = 0x00000002,
+    FOS_STRICTFILETYPES = 0x00000004,
+    FOS_NOCHANGEDIR = 0x00000008,
+    FOS_PICKFOLDERS = 0x00000020,
+    FOS_FORCEFILESYSTEM = 0x00000040, // Ensure that items returned are filesystem items.
+    FOS_ALLNONSTORAGEITEMS = 0x00000080, // Allow choosing items that have no storage.
+    FOS_NOVALIDATE = 0x00000100,
+    FOS_ALLOWMULTISELECT = 0x00000200,
+    FOS_PATHMUSTEXIST = 0x00000800,
+    FOS_FILEMUSTEXIST = 0x00001000,
+    FOS_CREATEPROMPT = 0x00002000,
+    FOS_SHAREAWARE = 0x00004000,
+    FOS_NOREADONLYRETURN = 0x00008000,
+    FOS_NOTESTFILECREATE = 0x00010000,
+    FOS_HIDEMRUPLACES = 0x00020000,
+    FOS_HIDEPINNEDPLACES = 0x00040000,
+    FOS_NODEREFERENCELINKS = 0x00100000,
+    FOS_DONTADDTORECENT = 0x02000000,
+    FOS_FORCESHOWHIDDEN = 0x10000000,
+    FOS_DEFAULTNOMINIMODE = 0x20000000
+}
+
+[
+    object,
+    uuid(43826d1e-e718-42ee-bc55-a1e261c37bfe),
+    pointer_default(unique)
+]
+interface IShellItem : IUnknown
+{
+    HRESULT BindToHandler(
+        [in, unique] void* pbc,
+        [in] REFGUID bhid,
+        [in] REFIID riid,
+        [out, iid_is(riid)] void** ppv);
+
+    HRESULT GetParent([out] IShellItem** ppsi);
+
+    HRESULT GetDisplayName(
+        [in] uint sigdnName,
+        [out, string, annotation("_Outptr_result_nullonfailure_")] WCHAR** ppszName);
+
+    HRESULT GetAttributes(
+        [in] ULONG sfgaoMask,
+        [out] ULONG* psfgaoAttribs);
+
+    HRESULT Compare(
+        [in] IShellItem* psi,
+        [in] ULONG hint,
+        [out] int* piOrder);
+}
+
+[
+    object,
+    uuid(B63EA76D-1F85-456F-A19C-48159EFA858B),
+    pointer_default(unique)
+]
+interface IShellItemArray : IUnknown
+{
+    HRESULT BindToHandler([in, unique] void* pbc, [in] REFGUID bhid, [in] REFIID riid, [out, iid_is(riid)] void** ppvOut);
+
+    HRESULT GetPropertyStore([in] UINT flags, [in] REFIID riid, [out, iid_is(riid)] void** ppv);
+
+    HRESULT GetPropertyDescriptionList([in] void* keyType, [in] REFIID riid, [out, iid_is(riid)] void** ppv);
+
+    HRESULT GetAttributes([in] int AttribFlags, [in] UINT sfgaoMask, [out] UINT* psfgaoAttribs);
+
+    HRESULT GetCount([out] DWORD* pdwNumItems);
+
+    HRESULT GetItemAt([in] DWORD dwIndex, [out] IShellItem** ppsi);
+
+    HRESULT EnumItems([out] void** ppenumShellItems);
+}
+
+[
+    object,
+    uuid(B4DB1657-70D7-485E-8E3E-6FCB5A5C1802),
+    pointer_default(unique)
+]
+interface IModalWindow : IUnknown
+{
+    [local]
+    HRESULT Show(
+        [in, unique] HWND hwndOwner);
+}
+
+[
+    object,
+    uuid(42F85136-DB7E-439C-85F1-E4075D135FC8),
+    pointer_default(unique)
+]
+interface IFileDialog : IModalWindow
+{
+    HRESULT SetFileTypes(
+        [in] UINT cFileTypes,
+        [in, size_is(cFileTypes)] void* rgFilterSpec);
+
+    HRESULT SetFileTypeIndex([in] UINT iFileType);
+
+    HRESULT GetFileTypeIndex([out] UINT* piFileType);
+
+    HRESULT Advise(
+        [in] void* pfde,
+        [out] DWORD* pdwCookie);
+
+    HRESULT Unadvise([in] DWORD dwCookie);
+
+    HRESULT SetOptions([in] FILEOPENDIALOGOPTIONS fos);
+
+    HRESULT GetOptions([out] FILEOPENDIALOGOPTIONS* pfos);
+
+    HRESULT SetDefaultFolder([in] IShellItem* psi);
+
+    HRESULT SetFolder([in] IShellItem* psi);
+
+    HRESULT GetFolder([out] IShellItem** ppsi);
+
+    HRESULT GetCurrentSelection([out] IShellItem** ppsi);
+
+    HRESULT SetFileName([in, string] WCHAR* pszName);
+
+    HRESULT GetFileName([out, string] WCHAR** pszName);
+
+    HRESULT SetTitle([in, string] WCHAR* pszTitle);
+
+    HRESULT SetOkButtonLabel([in, string] WCHAR* pszText);
+
+    HRESULT SetFileNameLabel([in, string] WCHAR* pszLabel);
+
+    HRESULT GetResult([out] IShellItem** ppsi);
+
+    HRESULT AddPlace(
+        [in] IShellItem* psi,
+        [in] INT32 fdap);
+
+    HRESULT SetDefaultExtension([in, string] WCHAR* pszDefaultExtension);
+
+    HRESULT Close([in] HRESULT hr);
+
+    HRESULT SetClientGuid([in] REFGUID guid);
+
+    HRESULT ClearClientData();
+
+    HRESULT SetFilter([in] void* pFilter);
+}
+
+[
+    object,
+    uuid(D57C7288-D4AD-4768-BE02-9D969532D960),
+    pointer_default(unique)
+]
+interface IFileOpenDialog : IFileDialog
+{
+    HRESULT GetResults(
+        [out] IShellItemArray** ppenum);
+
+    HRESULT GetSelectedItems(
+        [out] IShellItemArray** ppsai);
+}
diff --git a/src/iOS/Avalonia.iOS/Avalonia.iOS.csproj b/src/iOS/Avalonia.iOS/Avalonia.iOS.csproj
index d5b95b3151..c219e08c8b 100644
--- a/src/iOS/Avalonia.iOS/Avalonia.iOS.csproj
+++ b/src/iOS/Avalonia.iOS/Avalonia.iOS.csproj
@@ -1,5 +1,4 @@
-<Project>
-  <Import Project="Sdk.props" Sdk="MSBuild.Sdk.Extras" />
+<Project Sdk="MSBuild.Sdk.Extras">
   <PropertyGroup>
     <TargetFramework>xamarin.ios10</TargetFramework>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
@@ -20,5 +19,4 @@
     <ProjectReference Include="..\..\..\packages\Avalonia\Avalonia.csproj" />
     <ProjectReference Include="..\..\Skia\Avalonia.Skia\Avalonia.Skia.csproj" />
   </ItemGroup>
-  <Import Project="Sdk.targets" Sdk="MSBuild.Sdk.Extras" />
 </Project>
diff --git a/src/tools/MicroComGenerator/ParseException.cs b/src/tools/MicroComGenerator/ParseException.cs
index dfa8dcfe54..cb54918100 100644
--- a/src/tools/MicroComGenerator/ParseException.cs
+++ b/src/tools/MicroComGenerator/ParseException.cs
@@ -7,7 +7,7 @@ namespace MicroComGenerator
         public int Line { get; }
         public int Position { get; }
 
-        public ParseException(string message, int line, int position) : base(message)
+        public ParseException(string message, int line, int position) : base($"({line}, {position}) {message}")
         {
             Line = line;
             Position = position;
diff --git a/tests/Avalonia.Base.UnitTests/Collections/AvaloniaListTests.cs b/tests/Avalonia.Base.UnitTests/Collections/AvaloniaListTests.cs
index d5ac01a092..f5ae4cc1e0 100644
--- a/tests/Avalonia.Base.UnitTests/Collections/AvaloniaListTests.cs
+++ b/tests/Avalonia.Base.UnitTests/Collections/AvaloniaListTests.cs
@@ -357,5 +357,157 @@ namespace Avalonia.Base.UnitTests.Collections
 
             Assert.Equal(target, result);
         }
+
+        [Fact]
+        public void RemoveAll_Should_Send_Single_Notification_For_Sequential_Range()
+        {
+            var target = new AvaloniaList<string>(Enumerable.Range(0, 10).Select(x => $"Item {x}"));
+            var toRemove = new[] { "Item 5", "Item 6", "Item 7" };
+            var raised = 0;
+
+            target.CollectionChanged += (s, e) =>
+            {
+                Assert.Equal(NotifyCollectionChangedAction.Remove, e.Action);
+                Assert.Equal(5, e.OldStartingIndex);
+                Assert.Equal(toRemove, e.OldItems);
+                ++raised;
+            };
+
+            target.RemoveAll(toRemove);
+
+            Assert.Equal(1, raised);
+        }
+
+        [Fact]
+        public void RemoveAll_Should_Send_Single_Notification_For_Sequential_Range_With_Duplicate_Source_Items()
+        {
+            var items = Enumerable.Range(0, 20).Select(x => $"Item {x / 2}");
+            var target = new AvaloniaList<string>(items);
+            var toRemove = new[] { "Item 5", "Item 6", "Item 7" };
+            var raised = 0;
+
+            target.CollectionChanged += (s, e) =>
+            {
+                Assert.Equal(NotifyCollectionChangedAction.Remove, e.Action);
+                Assert.Equal(10, e.OldStartingIndex);
+
+                Assert.Equal(new[] 
+                { 
+                    "Item 5",
+                    "Item 5",
+                    "Item 6",
+                    "Item 6",
+                    "Item 7",
+                    "Item 7",
+                }, e.OldItems);
+                ++raised;
+            };
+
+            target.RemoveAll(toRemove);
+
+            Assert.Equal(1, raised);
+        }
+
+        [Fact]
+        public void RemoveAll_Should_Send_Multiple_Notifications_For_Non_Sequential_Range()
+        {
+            var target = new AvaloniaList<string>(Enumerable.Range(0, 10).Select(x => $"Item {x}"));
+            var raised = 0;
+            var toRemove = new[] 
+            {
+                new[] { "Item 2", "Item 3" },
+                new[] { "Item 5", "Item 6" }
+            };
+
+            target.CollectionChanged += (s, e) =>
+            {
+                Assert.Equal(NotifyCollectionChangedAction.Remove, e.Action);
+                
+                if (raised == 0)
+                {
+                    Assert.Equal(5, e.OldStartingIndex);
+                    Assert.Equal(toRemove[1], e.OldItems);
+                }
+                else
+                {
+                    Assert.Equal(2, e.OldStartingIndex);
+                    Assert.Equal(toRemove[0], e.OldItems);
+                }
+
+                ++raised;
+            };
+
+            target.RemoveAll(toRemove[0].Concat(toRemove[1]));
+
+            Assert.Equal(2, raised);
+        }
+
+        [Fact]
+        public void RemoveAll_Should_Send_Multiple_Notifications_For_Sequential_Range_With_Nonsequential_Duplicate_Source_Items()
+        {
+            var items = Enumerable.Range(0, 10).Select(x => $"Item {x}");
+            var target = new AvaloniaList<string>(items.Concat(items));
+            var raised = 0;
+            var toRemove = new[] { "Item 5", "Item 6", "Item 7" };
+
+            target.CollectionChanged += (s, e) =>
+            {
+                Assert.Equal(NotifyCollectionChangedAction.Remove, e.Action);
+
+                if (raised == 0)
+                {
+                    Assert.Equal(15, e.OldStartingIndex);
+                    Assert.Equal(toRemove, e.OldItems);
+                }
+                else
+                {
+                    Assert.Equal(5, e.OldStartingIndex);
+                    Assert.Equal(toRemove, e.OldItems);
+                }
+
+                ++raised;
+            };
+
+            target.RemoveAll(toRemove);
+
+            Assert.Equal(2, raised);
+        }
+
+        [Fact]
+        public void RemoveAll_Should_Not_Send_Notification_For_Items_Not_Present()
+        {
+            var target = new AvaloniaList<string>(Enumerable.Range(0, 10).Select(x => $"Item {x}"));
+            var toRemove = new[] { "Item 5", "Item 6", "Item 7", "Not present" };
+            var raised = 0;
+
+            target.CollectionChanged += (s, e) =>
+            {
+                Assert.Equal(NotifyCollectionChangedAction.Remove, e.Action);
+                Assert.Equal(5, e.OldStartingIndex);
+                Assert.Equal(toRemove.Take(3).ToArray(), e.OldItems);
+                ++raised;
+            };
+
+            target.RemoveAll(toRemove);
+
+            Assert.Equal(1, raised);
+        }
+
+        [Fact]
+        public void RemoveAll_Should_Handle_Empty_List()
+        {
+            var target = new AvaloniaList<string>();
+            var toRemove = new[] { "Item 5", "Item 6", "Item 7" };
+            var raised = 0;
+
+            target.CollectionChanged += (s, e) =>
+            {
+                ++raised;
+            };
+
+            target.RemoveAll(toRemove);
+
+            Assert.Equal(0, raised);
+        }
     }
 }
diff --git a/tests/Avalonia.Controls.UnitTests/TextBoxTests.cs b/tests/Avalonia.Controls.UnitTests/TextBoxTests.cs
index cb20071860..23cae8fd0d 100644
--- a/tests/Avalonia.Controls.UnitTests/TextBoxTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/TextBoxTests.cs
@@ -784,6 +784,54 @@ namespace Avalonia.Controls.UnitTests
             }
         }
 
+        [Fact]
+        public void Setting_SelectedText_Should_Fire_Single_Text_Changed_Notification()
+        {
+            using (UnitTestApplication.Start(Services))
+            {
+                var target = new TextBox
+                {
+                    Template = CreateTemplate(),
+                    Text = "0123",
+                    AcceptsReturn = true,
+                    AcceptsTab = true,
+                    SelectionStart = 1,
+                    SelectionEnd = 3,
+                };
+
+                var values = new List<string>();
+                target.GetObservable(TextBox.TextProperty).Subscribe(x => values.Add(x));
+
+                target.SelectedText = "A";
+
+                Assert.Equal(new[] { "0123", "0A3" }, values);
+            }
+        }
+
+        [Fact]
+        public void Entering_Text_With_SelectedText_Should_Fire_Single_Text_Changed_Notification()
+        {
+            using (UnitTestApplication.Start(Services))
+            {
+                var target = new TextBox
+                {
+                    Template = CreateTemplate(),
+                    Text = "0123",
+                    AcceptsReturn = true,
+                    AcceptsTab = true,
+                    SelectionStart = 1,
+                    SelectionEnd = 3,
+                };
+
+                var values = new List<string>();
+                target.GetObservable(TextBox.TextProperty).Subscribe(x => values.Add(x));
+
+                RaiseTextEvent(target, "A");
+
+                Assert.Equal(new[] { "0123", "0A3" }, values);
+            }
+        }
+
         private static TestServices FocusServices => TestServices.MockThreadingInterface.With(
             focusManager: new FocusManager(),
             keyboardDevice: () => new KeyboardDevice(),