diff --git a/Avalonia.Desktop.slnf b/Avalonia.Desktop.slnf
index 477aaec6a8..d4cde99240 100644
--- a/Avalonia.Desktop.slnf
+++ b/Avalonia.Desktop.slnf
@@ -8,9 +8,9 @@
       "samples\\GpuInterop\\GpuInterop.csproj",
       "samples\\IntegrationTestApp\\IntegrationTestApp.csproj",
       "samples\\MiniMvvm\\MiniMvvm.csproj",
+      "samples\\ReactiveUIDemo\\ReactiveUIDemo.csproj",
       "samples\\SampleControls\\ControlSamples.csproj",
       "samples\\Sandbox\\Sandbox.csproj",
-      "samples\\ReactiveUIDemo\\ReactiveUIDemo.csproj",
       "src\\Avalonia.Base\\Avalonia.Base.csproj",
       "src\\Avalonia.Build.Tasks\\Avalonia.Build.Tasks.csproj",
       "src\\Avalonia.Controls.ColorPicker\\Avalonia.Controls.ColorPicker.csproj",
@@ -41,6 +41,7 @@
       "src\\Windows\\Avalonia.Direct2D1\\Avalonia.Direct2D1.csproj",
       "src\\Windows\\Avalonia.Win32.Interop\\Avalonia.Win32.Interop.csproj",
       "src\\Windows\\Avalonia.Win32\\Avalonia.Win32.csproj",
+      "src\\tools\\Avalonia.Generators\\Avalonia.Generators.csproj",
       "src\\tools\\DevAnalyzers\\DevAnalyzers.csproj",
       "src\\tools\\DevGenerators\\DevGenerators.csproj",
       "src\\tools\\PublicAnalyzers\\Avalonia.Analyzers.csproj",
@@ -63,4 +64,4 @@
       "tests\\Avalonia.UnitTests\\Avalonia.UnitTests.csproj"
     ]
   }
-}
+}
\ No newline at end of file
diff --git a/samples/ControlCatalog/Pages/DialogsPage.xaml.cs b/samples/ControlCatalog/Pages/DialogsPage.xaml.cs
index e5f29abb68..02e3027aa6 100644
--- a/samples/ControlCatalog/Pages/DialogsPage.xaml.cs
+++ b/samples/ControlCatalog/Pages/DialogsPage.xaml.cs
@@ -324,9 +324,9 @@ namespace ControlCatalog.Pages
                         mappedResults.Add("+> " + FullPathOrName(selectedItem));
                         if (selectedItem is IStorageFolder folder)
                         {
-                            foreach (var innerItems in await folder.GetItemsAsync())
+                            await foreach (var innerItem in folder.GetItemsAsync())
                             {
-                                mappedResults.Add("++> " + FullPathOrName(innerItems));
+                                mappedResults.Add("++> " + FullPathOrName(innerItem));
                             }
                         }
                     }
diff --git a/samples/ControlCatalog/Pages/DragAndDropPage.xaml.cs b/samples/ControlCatalog/Pages/DragAndDropPage.xaml.cs
index 26430b4b61..7fb5bec589 100644
--- a/samples/ControlCatalog/Pages/DragAndDropPage.xaml.cs
+++ b/samples/ControlCatalog/Pages/DragAndDropPage.xaml.cs
@@ -104,8 +104,12 @@ namespace ControlCatalog.Pages
                         }
                         else if (item is IStorageFolder folder)
                         {
-                            var items = await folder.GetItemsAsync();
-                            contentStr += $"Folder {item.Name}: items {items.Count}{Environment.NewLine}{Environment.NewLine}";
+                            var childrenCount = 0;
+                            await foreach (var _ in folder.GetItemsAsync())
+                            {
+                                childrenCount++;
+                            }
+                            contentStr += $"Folder {item.Name}: items {childrenCount}{Environment.NewLine}{Environment.NewLine}";
                         }
                     }
 
diff --git a/src/Android/Avalonia.Android/Platform/Storage/AndroidStorageItem.cs b/src/Android/Avalonia.Android/Platform/Storage/AndroidStorageItem.cs
index 0a34e6077c..8052b3911a 100644
--- a/src/Android/Avalonia.Android/Platform/Storage/AndroidStorageItem.cs
+++ b/src/Android/Avalonia.Android/Platform/Storage/AndroidStorageItem.cs
@@ -131,19 +131,17 @@ internal class AndroidStorageFolder : AndroidStorageItem, IStorageBookmarkFolder
         return Task.FromResult(new StorageItemProperties());
     }
 
-    public async Task<IReadOnlyList<IStorageItem>> GetItemsAsync()
+    public async IAsyncEnumerable<IStorageItem> GetItemsAsync()
     {
         if (!await EnsureExternalFilesPermission(false))
         {
-            return Array.Empty<IStorageItem>();
+            yield break;
         }
-
-        List<IStorageItem> files = new List<IStorageItem>();
-
+        
         var contentResolver = Activity.ContentResolver;
         if (contentResolver == null)
         {
-            return files;
+            yield break;
         }
 
         var childrenUri = DocumentsContract.BuildChildDocumentsUriUsingTree(Uri!, DocumentsContract.GetTreeDocumentId(Uri));
@@ -168,12 +166,10 @@ internal class AndroidStorageFolder : AndroidStorageItem, IStorageBookmarkFolder
                         continue;
                     }
 
-                    files.Add(mime == DocumentsContract.Document.MimeTypeDir ? new AndroidStorageFolder(Activity, uri, false) :
-                        new AndroidStorageFile(Activity, uri));
+                    yield return mime == DocumentsContract.Document.MimeTypeDir ? new AndroidStorageFolder(Activity, uri, false) :
+                        new AndroidStorageFile(Activity, uri);
                 }
         }
-
-        return files;
     }       
 }
 
diff --git a/src/Avalonia.Base/AvaloniaProperty.cs b/src/Avalonia.Base/AvaloniaProperty.cs
index bda30c08fb..e98d9f0517 100644
--- a/src/Avalonia.Base/AvaloniaProperty.cs
+++ b/src/Avalonia.Base/AvaloniaProperty.cs
@@ -4,7 +4,6 @@ using System.Diagnostics.CodeAnalysis;
 using Avalonia.Data;
 using Avalonia.Data.Core;
 using Avalonia.PropertyStore;
-using Avalonia.Styling;
 using Avalonia.Utilities;
 
 namespace Avalonia
@@ -20,12 +19,20 @@ namespace Avalonia
         public static readonly object UnsetValue = new UnsetValueType();
 
         private static int s_nextId;
+
+        /// <summary>
+        /// Provides a metadata object for types which have no metadata of their own.
+        /// </summary>
         private readonly AvaloniaPropertyMetadata _defaultMetadata;
+
+        /// <summary>
+        /// Provides a fast path when the property has no metadata overrides.
+        /// </summary>
+        private KeyValuePair<Type, AvaloniaPropertyMetadata>? _singleMetadata;
+
         private readonly Dictionary<Type, AvaloniaPropertyMetadata> _metadata;
         private readonly Dictionary<Type, AvaloniaPropertyMetadata> _metadataCache = new Dictionary<Type, AvaloniaPropertyMetadata>();
 
-        private bool _hasMetadataOverrides;
-
         /// <summary>
         /// Initializes a new instance of the <see cref="AvaloniaProperty"/> class.
         /// </summary>
@@ -57,7 +64,8 @@ namespace Avalonia
             Id = s_nextId++;
 
             _metadata.Add(ownerType, metadata ?? throw new ArgumentNullException(nameof(metadata)));
-            _defaultMetadata = metadata;
+            _defaultMetadata = metadata.GenerateTypeSafeMetadata();
+            _singleMetadata = new(ownerType, metadata);
         }
 
         /// <summary>
@@ -80,9 +88,6 @@ namespace Avalonia
             Id = source.Id;
             _defaultMetadata = source._defaultMetadata;
 
-            // Properties that have different owner can't use fast path for metadata.
-            _hasMetadataOverrides = true;
-
             if (metadata != null)
             {
                 _metadata.Add(ownerType, metadata);
@@ -453,33 +458,14 @@ namespace Avalonia
         }
 
         /// <summary>
-        /// Gets the property metadata for the specified type.
+        /// Gets the <see cref="AvaloniaPropertyMetadata"/> which applies to this property when it is used with the specified type.
         /// </summary>
-        /// <typeparam name="T">The type.</typeparam>
-        /// <returns>
-        /// The property metadata.
-        /// </returns>
-        public AvaloniaPropertyMetadata GetMetadata<T>() where T : AvaloniaObject
-        {
-            return GetMetadata(typeof(T));
-        }
+        /// <typeparam name="T">The type for which to retrieve metadata.</typeparam>
+        public AvaloniaPropertyMetadata GetMetadata<T>() where T : AvaloniaObject => GetMetadata(typeof(T));
 
-        /// <summary>
-        /// Gets the property metadata for the specified type.
-        /// </summary>
-        /// <param name="type">The type.</param>
-        /// <returns>
-        /// The property metadata.
-        /// </returns>
-        public AvaloniaPropertyMetadata GetMetadata(Type type)
-        {
-            if (!_hasMetadataOverrides)
-            {
-                return _defaultMetadata;
-            }
-
-            return GetMetadataWithOverrides(type);
-        }
+        /// <inheritdoc cref="GetMetadata{T}"/>
+        /// <param name="type">The type for which to retrieve metadata.</param>
+        public AvaloniaPropertyMetadata GetMetadata(Type type) => GetMetadataWithOverrides(type);
 
         /// <summary>
         /// Checks whether the <paramref name="value"/> is valid for the property.
@@ -578,7 +564,7 @@ namespace Avalonia
             _metadata.Add(type, metadata);
             _metadataCache.Clear();
 
-            _hasMetadataOverrides = true;
+            _singleMetadata = null;
         }
 
         protected abstract IObservable<AvaloniaPropertyChangedEventArgs> GetChanged();
@@ -595,7 +581,12 @@ namespace Avalonia
                 return result;
             }
 
-            Type? currentType = type;
+            if (_singleMetadata is { } singleMetadata)
+            {
+                return _metadataCache[type] = singleMetadata.Key.IsAssignableFrom(type) ? singleMetadata.Value : _defaultMetadata;
+            }
+
+            var currentType = type;
 
             while (currentType != null)
             {
@@ -609,13 +600,11 @@ namespace Avalonia
                 currentType = currentType.BaseType;
             }
 
-            _metadataCache[type] = _defaultMetadata;
-
-            return _defaultMetadata;
+            return _metadataCache[type] = _defaultMetadata;
         }
 
         bool IPropertyInfo.CanGet => true;
-        bool IPropertyInfo.CanSet => true;
+        bool IPropertyInfo.CanSet => !IsReadOnly;
         object? IPropertyInfo.Get(object target) => ((AvaloniaObject)target).GetValue(this);
         void IPropertyInfo.Set(object target, object? value) => ((AvaloniaObject)target).SetValue(this, value);
     }
diff --git a/src/Avalonia.Base/AvaloniaPropertyMetadata.cs b/src/Avalonia.Base/AvaloniaPropertyMetadata.cs
index 62bb65351f..ec29d14693 100644
--- a/src/Avalonia.Base/AvaloniaPropertyMetadata.cs
+++ b/src/Avalonia.Base/AvaloniaPropertyMetadata.cs
@@ -5,7 +5,7 @@ namespace Avalonia
     /// <summary>
     /// Base class for avalonia property metadata.
     /// </summary>
-    public class AvaloniaPropertyMetadata
+    public abstract class AvaloniaPropertyMetadata
     {
         private BindingMode _defaultBindingMode;
 
@@ -61,5 +61,13 @@ namespace Avalonia
 
             EnableDataValidation ??= baseMetadata.EnableDataValidation;
         }
+
+        /// <summary>
+        /// Gets a copy of this object configured for use with any owner type.
+        /// </summary>
+        /// <remarks>
+        /// For example, delegates which receive the owner object should be removed.
+        /// </remarks>
+        public abstract AvaloniaPropertyMetadata GenerateTypeSafeMetadata();
     }
 }
diff --git a/src/Avalonia.Base/DirectPropertyMetadata`1.cs b/src/Avalonia.Base/DirectPropertyMetadata`1.cs
index 451ff6ce00..5471826f9f 100644
--- a/src/Avalonia.Base/DirectPropertyMetadata`1.cs
+++ b/src/Avalonia.Base/DirectPropertyMetadata`1.cs
@@ -45,5 +45,7 @@ namespace Avalonia
                 UnsetValue ??= src.UnsetValue;
             }
         }
+
+        public override AvaloniaPropertyMetadata GenerateTypeSafeMetadata() => new DirectPropertyMetadata<TValue>(UnsetValue, DefaultBindingMode, EnableDataValidation);
     }
 }
diff --git a/src/Avalonia.Base/Platform/Storage/FileIO/BclStorageFolder.cs b/src/Avalonia.Base/Platform/Storage/FileIO/BclStorageFolder.cs
index d8e3d91f75..e6551390d6 100644
--- a/src/Avalonia.Base/Platform/Storage/FileIO/BclStorageFolder.cs
+++ b/src/Avalonia.Base/Platform/Storage/FileIO/BclStorageFolder.cs
@@ -57,14 +57,16 @@ internal class BclStorageFolder : IStorageBookmarkFolder
         return Task.FromResult<IStorageFolder?>(null);
     }
 
-    public Task<IReadOnlyList<IStorageItem>> GetItemsAsync()
+    public async IAsyncEnumerable<IStorageItem> GetItemsAsync()
     {
-         var items = DirectoryInfo.GetDirectories()
+        var items = DirectoryInfo.EnumerateDirectories()
             .Select(d => (IStorageItem)new BclStorageFolder(d))
-            .Concat(DirectoryInfo.GetFiles().Select(f => new BclStorageFile(f)))
-            .ToArray();
+            .Concat(DirectoryInfo.EnumerateFiles().Select(f => new BclStorageFile(f)));
 
-         return Task.FromResult<IReadOnlyList<IStorageItem>>(items);
+        foreach (var item in items)
+        {
+            yield return item;
+        }
     }
 
     public virtual Task<string?> SaveBookmarkAsync()
diff --git a/src/Avalonia.Base/Platform/Storage/IStorageFolder.cs b/src/Avalonia.Base/Platform/Storage/IStorageFolder.cs
index 0ffb9f41c6..52b3256387 100644
--- a/src/Avalonia.Base/Platform/Storage/IStorageFolder.cs
+++ b/src/Avalonia.Base/Platform/Storage/IStorageFolder.cs
@@ -16,5 +16,5 @@ public interface IStorageFolder : IStorageItem
     /// <returns>
     /// When this method completes successfully, it returns a list of the files and folders in the current folder. Each item in the list is represented by an <see cref="IStorageItem"/> implementation object.
     /// </returns>
-    Task<IReadOnlyList<IStorageItem>> GetItemsAsync();
+    IAsyncEnumerable<IStorageItem> GetItemsAsync();
 }
diff --git a/src/Avalonia.Base/StyledProperty.cs b/src/Avalonia.Base/StyledProperty.cs
index 5052840013..dfe5a44f1b 100644
--- a/src/Avalonia.Base/StyledProperty.cs
+++ b/src/Avalonia.Base/StyledProperty.cs
@@ -18,7 +18,10 @@ namespace Avalonia
         /// <param name="ownerType">The type of the class that registers the property.</param>
         /// <param name="metadata">The property metadata.</param>
         /// <param name="inherits">Whether the property inherits its value.</param>
-        /// <param name="validate">A value validation callback.</param>
+        /// <param name="validate">
+        /// <para>A method which returns "false" for values that are never valid for this property.</para>
+        /// <para>This method is not part of the property's metadata and so cannot be changed after registration.</para>
+        /// </param>
         /// <param name="notifying">A <see cref="AvaloniaProperty.Notifying"/> callback.</param>
         public StyledProperty(
             string name,
@@ -41,7 +44,7 @@ namespace Avalonia
         }
 
         /// <summary>
-        /// Gets the value validation callback for the property.
+        /// A method which returns "false" for values that are never valid for this property.
         /// </summary>
         public Func<TValue, bool>? ValidateValue { get; }
 
diff --git a/src/Avalonia.Base/StyledPropertyMetadata`1.cs b/src/Avalonia.Base/StyledPropertyMetadata`1.cs
index 6f10de3651..9db460dba3 100644
--- a/src/Avalonia.Base/StyledPropertyMetadata`1.cs
+++ b/src/Avalonia.Base/StyledPropertyMetadata`1.cs
@@ -58,5 +58,7 @@ namespace Avalonia
                 }
             }
         }
+
+        public override AvaloniaPropertyMetadata GenerateTypeSafeMetadata() => new StyledPropertyMetadata<TValue>(DefaultValue, DefaultBindingMode, enableDataValidation: EnableDataValidation ?? false);
     }
 }
diff --git a/src/Avalonia.Controls.DataGrid/DataGrid.cs b/src/Avalonia.Controls.DataGrid/DataGrid.cs
index 91b65a1f72..72ebf10984 100644
--- a/src/Avalonia.Controls.DataGrid/DataGrid.cs
+++ b/src/Avalonia.Controls.DataGrid/DataGrid.cs
@@ -6066,8 +6066,9 @@ namespace Avalonia.Controls
             var numberOfItem = clipboardRowContent.Count;
             for (int cellIndex = 0; cellIndex < numberOfItem; cellIndex++)
             {
-                var cellContent = clipboardRowContent[cellIndex];
-                text.Append(cellContent.Content);
+                var cellContent = clipboardRowContent[cellIndex].Content?.ToString();
+                cellContent = cellContent?.Replace("\"", "\"\"");
+                text.Append($"\"{cellContent}\"");
                 if (cellIndex < numberOfItem - 1)
                 {
                     text.Append('\t');
diff --git a/src/Avalonia.Controls/Platform/IPopupImpl.cs b/src/Avalonia.Controls/Platform/IPopupImpl.cs
index cd86045dee..320130bc91 100644
--- a/src/Avalonia.Controls/Platform/IPopupImpl.cs
+++ b/src/Avalonia.Controls/Platform/IPopupImpl.cs
@@ -9,7 +9,7 @@ namespace Avalonia.Platform
     [Unstable]
     public interface IPopupImpl : IWindowBaseImpl
     {
-        IPopupPositioner PopupPositioner { get; }
+        IPopupPositioner? PopupPositioner { get; }
 
         void SetWindowManagerAddShadowHint(bool enabled);
     }
diff --git a/src/Avalonia.Controls/Primitives/PopupRoot.cs b/src/Avalonia.Controls/Primitives/PopupRoot.cs
index b3436d4176..952ba92e9b 100644
--- a/src/Avalonia.Controls/Primitives/PopupRoot.cs
+++ b/src/Avalonia.Controls/Primitives/PopupRoot.cs
@@ -95,7 +95,7 @@ namespace Avalonia.Controls.Primitives
 
         private void UpdatePosition()
         {
-            PlatformImpl?.PopupPositioner.Update(_positionerParameters);
+            PlatformImpl?.PopupPositioner?.Update(_positionerParameters);
         }
 
         public void ConfigurePosition(Visual target, PlacementMode placement, Point offset,
diff --git a/src/Avalonia.Controls/ToolTipService.cs b/src/Avalonia.Controls/ToolTipService.cs
index 9ec9013679..d983309a72 100644
--- a/src/Avalonia.Controls/ToolTipService.cs
+++ b/src/Avalonia.Controls/ToolTipService.cs
@@ -42,11 +42,12 @@ namespace Avalonia.Controls
                 {
                     Close(control);
                 }
-                else
+                else 
                 {
-                    var tip = control.GetValue(ToolTip.ToolTipProperty);
-
-                    tip!.Content = e.NewValue;
+                    if (control.GetValue(ToolTip.ToolTipProperty) is { } tip)
+                    {
+                        tip.Content = e.NewValue;
+                    }
                 }
             }
         }
diff --git a/src/Avalonia.X11/X11Window.cs b/src/Avalonia.X11/X11Window.cs
index 6634ab4d7b..22748f6aa3 100644
--- a/src/Avalonia.X11/X11Window.cs
+++ b/src/Avalonia.X11/X11Window.cs
@@ -25,6 +25,9 @@ using Avalonia.X11.NativeDialogs;
 using static Avalonia.X11.XLib;
 // ReSharper disable IdentifierTypo
 // ReSharper disable StringLiteralTypo
+
+#nullable enable
+
 namespace Avalonia.X11
 {
     internal unsafe partial class X11Window : IWindowImpl, IPopupImpl, IXI2Client
@@ -35,11 +38,11 @@ namespace Avalonia.X11
         private XConfigureEvent? _configure;
         private PixelPoint? _configurePoint;
         private bool _triggeredExpose;
-        private IInputRoot _inputRoot;
+        private IInputRoot? _inputRoot;
         private readonly MouseDevice _mouse;
         private readonly TouchDevice _touch;
         private readonly IKeyboardDevice _keyboard;
-        private readonly ITopLevelNativeMenuExporter _nativeMenuExporter;
+        private readonly ITopLevelNativeMenuExporter? _nativeMenuExporter;
         private readonly IStorageProvider _storageProvider;
         private readonly X11NativeControlHost _nativeControlHost;
         private PixelPoint? _position;
@@ -54,8 +57,8 @@ namespace Avalonia.X11
         private bool _wasMappedAtLeastOnce = false;
         private double? _scalingOverride;
         private bool _disabled;
-        private TransparencyHelper _transparencyHelper;
-        private RawEventGrouper _rawEventGrouper;
+        private TransparencyHelper? _transparencyHelper;
+        private RawEventGrouper? _rawEventGrouper;
         private bool _useRenderWindow = false;
         private bool _usePositioningFlags = false;
 
@@ -66,7 +69,7 @@ namespace Avalonia.X11
             WaitPaint
         }
         
-        public X11Window(AvaloniaX11Platform platform, IWindowImpl popupParent)
+        public X11Window(AvaloniaX11Platform platform, IWindowImpl? popupParent)
         {
             _platform = platform;
             _popup = popupParent != null;
@@ -196,7 +199,7 @@ namespace Avalonia.X11
 
             XFlush(_x11.Display);
             if(_popup)
-                PopupPositioner = new ManagedPopupPositioner(new ManagedPopupPositionerPopupImplHelper(popupParent, MoveResize));
+                PopupPositioner = new ManagedPopupPositioner(new ManagedPopupPositionerPopupImplHelper(popupParent!, MoveResize));
             if (platform.Options.UseDBusMenu)
                 _nativeMenuExporter = DBusMenuExporter.TryCreateTopLevelNativeMenu(_handle);
             _nativeControlHost = new X11NativeControlHost(_platform, this);
@@ -214,7 +217,7 @@ namespace Avalonia.X11
 
             _storageProvider = new CompositeStorageProvider(new[]
             {
-                () => _platform.Options.UseDBusFilePicker ? DBusSystemDialog.TryCreateAsync(Handle) : Task.FromResult<IStorageProvider>(null),
+                () => _platform.Options.UseDBusFilePicker ? DBusSystemDialog.TryCreateAsync(Handle) : Task.FromResult<IStorageProvider?>(null),
                 () => GtkSystemDialog.TryCreate(this)
             });
         }
@@ -351,17 +354,17 @@ namespace Avalonia.X11
         public double DesktopScaling => RenderScaling;
 
         public IEnumerable<object> Surfaces { get; }
-        public Action<RawInputEventArgs> Input { get; set; }
-        public Action<Rect> Paint { get; set; }
-        public Action<Size, PlatformResizeReason> Resized { get; set; }
+        public Action<RawInputEventArgs>? Input { get; set; }
+        public Action<Rect>? Paint { get; set; }
+        public Action<Size, PlatformResizeReason>? Resized { get; set; }
         //TODO
-        public Action<double> ScalingChanged { get; set; }
-        public Action Deactivated { get; set; }
-        public Action Activated { get; set; }
-        public Func<WindowCloseReason, bool> Closing { get; set; }
-        public Action<WindowState> WindowStateChanged { get; set; }
+        public Action<double>? ScalingChanged { get; set; }
+        public Action? Deactivated { get; set; }
+        public Action? Activated { get; set; }
+        public Func<WindowCloseReason, bool>? Closing { get; set; }
+        public Action<WindowState>? WindowStateChanged { get; set; }
 
-        public Action<WindowTransparencyLevel> TransparencyLevelChanged
+        public Action<WindowTransparencyLevel>? TransparencyLevelChanged
         {
             get => _transparencyHelper?.TransparencyLevelChanged;
             set
@@ -371,7 +374,7 @@ namespace Avalonia.X11
             }
         }
 
-        public Action<bool> ExtendClientAreaToDecorationsChanged { get; set; }
+        public Action<bool>? ExtendClientAreaToDecorationsChanged { get; set; }
 
         public Thickness ExtendedMargins { get; } = new Thickness();
 
@@ -379,15 +382,18 @@ namespace Avalonia.X11
 
         public bool IsClientAreaExtendedToDecorations { get; }
 
-        public Action Closed { get; set; }
-        public Action<PixelPoint> PositionChanged { get; set; }
-        public Action LostFocus { get; set; }
+        public Action? Closed { get; set; }
+        public Action<PixelPoint>? PositionChanged { get; set; }
+        public Action? LostFocus { get; set; }
 
         public IRenderer CreateRenderer(IRenderRoot root) =>
             new CompositingRenderer(root, _platform.Compositor, () => Surfaces);
 
         private void OnEvent(ref XEvent ev)
         {
+            if (_inputRoot is null)
+                return;
+
             if (ev.type == XEventName.MapNotify)
             {
                 _mapped = true;
@@ -434,7 +440,8 @@ namespace Avalonia.X11
                             2 => RawPointerEventType.MiddleButtonDown,
                             3 => RawPointerEventType.RightButtonDown,
                             8 => RawPointerEventType.XButton1Down,
-                            9 => RawPointerEventType.XButton2Down
+                            9 => RawPointerEventType.XButton2Down,
+                            _ => throw new NotSupportedException("Unexepected RawPointerEventType.")
                         },
                         ref ev, ev.ButtonEvent.state);
                 else
@@ -462,7 +469,8 @@ namespace Avalonia.X11
                             2 => RawPointerEventType.MiddleButtonUp,
                             3 => RawPointerEventType.RightButtonUp,
                             8 => RawPointerEventType.XButton1Up,
-                            9 => RawPointerEventType.XButton2Up
+                            9 => RawPointerEventType.XButton2Up,
+                            _ => throw new NotSupportedException("Unexepected RawPointerEventType.")
                         },
                         ref ev, ev.ButtonEvent.state);
             }
@@ -618,7 +626,7 @@ namespace Avalonia.X11
             {
                 // Occurs once the window has been mapped, which is the earliest the extents
                 // can be retrieved, so invoke event to force update of TopLevel.FrameSize.
-                Resized.Invoke(ClientSize, PlatformResizeReason.Unspecified);
+                Resized?.Invoke(ClientSize, PlatformResizeReason.Unspecified);
             }
 
             if (atom == _x11.Atoms._NET_WM_STATE)
@@ -712,6 +720,8 @@ namespace Avalonia.X11
 
         private void DispatchInput(RawInputEventArgs args)
         {
+            if (_inputRoot is null)
+                return;
             Input?.Invoke(args);
             if (!args.Handled && args is RawKeyEventArgsWithText text && !string.IsNullOrEmpty(text.Text))
                 Input?.Invoke(new RawTextInputEventArgs(_keyboard, args.Timestamp, _inputRoot, text.Text));
@@ -744,11 +754,13 @@ namespace Avalonia.X11
             if (args is RawDragEvent drag)
                 drag.Location = drag.Location / RenderScaling;
             
-            _rawEventGrouper.HandleEvent(args);
+            _rawEventGrouper?.HandleEvent(args);
         }
 
         private void MouseEvent(RawPointerEventType type, ref XEvent ev, XModifierMask mods)
         {
+            if (_inputRoot is null)
+                return;
             var mev = new RawPointerEventArgs(
                 _mouse, (ulong)ev.ButtonEvent.time.ToInt64(), _inputRoot,
                 type, new Point(ev.ButtonEvent.x, ev.ButtonEvent.y), TranslateModifiers(mods));
@@ -783,7 +795,7 @@ namespace Avalonia.X11
 
         }
 
-        public IInputRoot InputRoot => _inputRoot;
+        public IInputRoot? InputRoot => _inputRoot;
         
         public void SetInputRoot(IInputRoot inputRoot)
         {
@@ -795,7 +807,7 @@ namespace Avalonia.X11
             Cleanup();            
         }
 
-        public virtual object TryGetFeature(Type featureType)
+        public virtual object? TryGetFeature(Type featureType)
         {
             if (featureType == typeof(ITopLevelNativeMenuExporter))
             {
@@ -953,7 +965,7 @@ namespace Avalonia.X11
             UpdateSizeHints(null);
         }
 
-        public void SetCursor(ICursorImpl cursor)
+        public void SetCursor(ICursorImpl? cursor)
         {
             if (cursor == null)
                 XDefineCursor(_x11.Display, _handle, _x11.DefaultCursor);
@@ -996,7 +1008,7 @@ namespace Avalonia.X11
         public IMouseDevice MouseDevice => _mouse;
         public TouchDevice TouchDevice => _touch;
 
-        public IPopupImpl CreatePopup() 
+        public IPopupImpl? CreatePopup() 
             => _platform.Options.OverlayPopups ? null : new X11Window(_platform, this);
 
         public void Activate()
@@ -1082,7 +1094,7 @@ namespace Avalonia.X11
             BeginMoveResize(side, e);
         }
 
-        public void SetTitle(string title)
+        public void SetTitle(string? title)
         {
             if (string.IsNullOrEmpty(title))
             {
@@ -1161,9 +1173,9 @@ namespace Avalonia.X11
         {
         }
 
-        public Action GotInputWhenDisabled { get; set; }
+        public Action? GotInputWhenDisabled { get; set; }
 
-        public void SetIcon(IWindowIconImpl icon)
+        public void SetIcon(IWindowIconImpl? icon)
         {
             if (icon != null)
             {
@@ -1218,7 +1230,7 @@ namespace Avalonia.X11
             );
         }
 
-        public IPopupPositioner PopupPositioner { get; }
+        public IPopupPositioner? PopupPositioner { get; }
 
         public void SetTransparencyLevelHint(WindowTransparencyLevel transparencyLevel) =>
             _transparencyHelper?.SetTransparencyRequest(transparencyLevel);
diff --git a/src/Browser/Avalonia.Browser/Interop/GeneralHelpers.cs b/src/Browser/Avalonia.Browser/Interop/GeneralHelpers.cs
index 6e3b41c05b..67d1cfb776 100644
--- a/src/Browser/Avalonia.Browser/Interop/GeneralHelpers.cs
+++ b/src/Browser/Avalonia.Browser/Interop/GeneralHelpers.cs
@@ -1,4 +1,5 @@
 using System.Runtime.InteropServices.JavaScript;
+using System.Threading.Tasks;
 
 namespace Avalonia.Browser.Interop;
 
@@ -8,15 +9,22 @@ internal static partial class GeneralHelpers
     public static partial JSObject[] ItemsArrayAt(JSObject jsObject, string key);
     public static JSObject[] GetPropertyAsJSObjectArray(this JSObject jsObject, string key) => ItemsArrayAt(jsObject, key);
     
+    [JSImport("GeneralHelpers.itemAt", AvaloniaModule.MainModuleName)]
+    public static partial JSObject ItemAtInt(JSObject jsObject, int key);
+    public static JSObject GetArrayItem(this JSObject jsObject, int key) => ItemAtInt(jsObject, key);
+    
     [JSImport("GeneralHelpers.itemsArrayAt", AvaloniaModule.MainModuleName)]
     public static partial string[] ItemsArrayAtAsStrings(JSObject jsObject, string key);
     public static string[] GetPropertyAsStringArray(this JSObject jsObject, string key) => ItemsArrayAtAsStrings(jsObject, key);
     
     [JSImport("GeneralHelpers.callMethod", AvaloniaModule.MainModuleName)]
-    public static partial string IntCallMethodString(JSObject jsObject, string name);
+    public static partial string IntCallMethodStr(JSObject jsObject, string name);
+    [JSImport("GeneralHelpers.callMethod", AvaloniaModule.MainModuleName)]
+    public static partial string IntCallMethodStrStr(JSObject jsObject, string name, string arg1);
     [JSImport("GeneralHelpers.callMethod", AvaloniaModule.MainModuleName)]
-    public static partial string IntCallMethodStringString(JSObject jsObject, string name, string arg1);
+    public static partial Task<JSObject?> IntCallMethodPromiseObj(JSObject jsObject, string name);
 
-    public static string CallMethodString(this JSObject jsObject, string name) => IntCallMethodString(jsObject, name);
-    public static string CallMethodString(this JSObject jsObject, string name, string arg1) => IntCallMethodStringString(jsObject, name, arg1);
+    public static string CallMethodString(this JSObject jsObject, string name) => IntCallMethodStr(jsObject, name);
+    public static string CallMethodString(this JSObject jsObject, string name, string arg1) => IntCallMethodStrStr(jsObject, name, arg1);
+    public static Task<JSObject?> CallMethodObjectAsync(this JSObject jsObject, string name) => IntCallMethodPromiseObj(jsObject, name);
 }
diff --git a/src/Browser/Avalonia.Browser/Interop/StorageHelper.cs b/src/Browser/Avalonia.Browser/Interop/StorageHelper.cs
index 2d96ee8d1f..dc3372d2d0 100644
--- a/src/Browser/Avalonia.Browser/Interop/StorageHelper.cs
+++ b/src/Browser/Avalonia.Browser/Interop/StorageHelper.cs
@@ -40,9 +40,9 @@ internal static partial class StorageHelper
     [JSImport("StorageItem.openRead", AvaloniaModule.StorageModuleName)]
     public static partial Task<JSObject> OpenRead(JSObject item);
 
-    [JSImport("StorageItem.getItems", AvaloniaModule.StorageModuleName)]
-    [return: JSMarshalAs<JSType.Promise<JSType.Object>>]
-    public static partial Task<JSObject?> GetItems(JSObject item);
+    [JSImport("StorageItem.getItemsIterator", AvaloniaModule.StorageModuleName)]
+    [return: JSMarshalAs<JSType.Object>]
+    public static partial JSObject? GetItemsIterator(JSObject item);
 
     [JSImport("StorageItems.itemsArray", AvaloniaModule.StorageModuleName)]
     public static partial JSObject[] ItemsArray(JSObject item);
diff --git a/src/Browser/Avalonia.Browser/Storage/BrowserStorageProvider.cs b/src/Browser/Avalonia.Browser/Storage/BrowserStorageProvider.cs
index fc32b3b4f7..fcb956f294 100644
--- a/src/Browser/Avalonia.Browser/Storage/BrowserStorageProvider.cs
+++ b/src/Browser/Avalonia.Browser/Storage/BrowserStorageProvider.cs
@@ -258,24 +258,45 @@ internal class JSStorageFolder : JSStorageItem, IStorageBookmarkFolder
     {
     }
 
-    public async Task<IReadOnlyList<IStorageItem>> GetItemsAsync()
+    public async IAsyncEnumerable<IStorageItem> GetItemsAsync()
     {
-        using var items = await StorageHelper.GetItems(FileHandle);
-        if (items is null)
+        using var itemsIterator = StorageHelper.GetItemsIterator(FileHandle);
+        if (itemsIterator is null)
         {
-            return Array.Empty<IStorageItem>();
+            yield break;
         }
 
-        var itemsArray = StorageHelper.ItemsArray(items);
+        while (true)
+        {
+            var nextResult = await itemsIterator.CallMethodObjectAsync("next");
+            if (nextResult is null)
+            {
+                yield break;
+            }
+
+            var isDone = nextResult.GetPropertyAsBoolean("done");
+            if (isDone)
+            {
+                yield break;
+            }
 
-        return itemsArray
-            .Select(reference => reference.GetPropertyAsString("kind") switch
+            var valArray = nextResult.GetPropertyAsJSObject("value");
+            var storageItem = valArray?.GetArrayItem(1); // 0 - item name, 1 - item instance
+            if (storageItem is null)
             {
-                "directory" => (IStorageItem)new JSStorageFolder(reference),
-                "file" => new JSStorageFile(reference),
-                _ => null
-            })
-            .Where(i => i is not null)
-            .ToArray()!;
+                yield break;
+            }
+
+            var kind = storageItem.GetPropertyAsString("kind");
+            switch (kind)
+            {
+                case "directory":
+                    yield return new JSStorageFolder(storageItem);
+                    break;
+                case "file":
+                    yield return new JSStorageFile(storageItem);
+                    break;
+            }
+        }
     }
 }
diff --git a/src/Browser/Avalonia.Browser/webapp/modules/avalonia/generalHelpers.ts b/src/Browser/Avalonia.Browser/webapp/modules/avalonia/generalHelpers.ts
index fa001006ab..31d167e38d 100644
--- a/src/Browser/Avalonia.Browser/webapp/modules/avalonia/generalHelpers.ts
+++ b/src/Browser/Avalonia.Browser/webapp/modules/avalonia/generalHelpers.ts
@@ -1,5 +1,5 @@
 export class GeneralHelpers {
-    public static itemsArrayAt(instance: any, key: string): any[] {
+    public static itemsArrayAt(instance: any, key: any): any[] {
         const items = instance[key];
         if (!items) {
             return [];
@@ -12,6 +12,11 @@ export class GeneralHelpers {
         return retItems;
     }
 
+    public static itemAt(instance: any, key: any): any {
+        const item = instance[key];
+        return item;
+    }
+
     public static callMethod(instance: any, name: string /*, args */): any {
         const args = Array.prototype.slice.call(arguments, 2);
         return instance[name].apply(instance, args);
diff --git a/src/Browser/Avalonia.Browser/webapp/modules/storage/storageItem.ts b/src/Browser/Avalonia.Browser/webapp/modules/storage/storageItem.ts
index f444717094..399e268915 100644
--- a/src/Browser/Avalonia.Browser/webapp/modules/storage/storageItem.ts
+++ b/src/Browser/Avalonia.Browser/webapp/modules/storage/storageItem.ts
@@ -89,16 +89,12 @@ export class StorageItem {
         }
     }
 
-    public static async getItems(item: StorageItem): Promise<StorageItems> {
+    public static getItemsIterator(item: StorageItem): any | null {
         if (item.kind !== "directory" || !item.handle) {
-            return new StorageItems([]);
+            return null;
         }
 
-        const items: StorageItem[] = [];
-        for await (const [, value] of (item.handle as any).entries()) {
-            items.push(new StorageItem(value));
-        }
-        return new StorageItems(items);
+        return (item.handle as any).entries();
     }
 
     private async verityPermissions(mode: "read" | "readwrite"): Promise<void | never> {
diff --git a/src/iOS/Avalonia.iOS/Storage/IOSStorageItem.cs b/src/iOS/Avalonia.iOS/Storage/IOSStorageItem.cs
index 27bd8faf64..baf31ebc73 100644
--- a/src/iOS/Avalonia.iOS/Storage/IOSStorageItem.cs
+++ b/src/iOS/Avalonia.iOS/Storage/IOSStorageItem.cs
@@ -114,8 +114,9 @@ internal sealed class IOSStorageFolder : IOSStorageItem, IStorageBookmarkFolder
     {
     }
 
-    public async Task<IReadOnlyList<IStorageItem>> GetItemsAsync()
+    public async IAsyncEnumerable<IStorageItem> GetItemsAsync()
     {
+        // TODO: find out if it can be lazily enumerated.
         var tcs = new TaskCompletionSource<IReadOnlyList<IStorageItem>>();
 
         new NSFileCoordinator().CoordinateRead(Url,
@@ -142,6 +143,10 @@ internal sealed class IOSStorageFolder : IOSStorageItem, IStorageBookmarkFolder
             throw new NSErrorException(error);
         }
 
-        return await tcs.Task;
+        var items = await tcs.Task;
+        foreach (var item in items)
+        {
+            yield return item;
+        }
     }
 }
diff --git a/tests/Avalonia.Base.UnitTests/AvaloniaPropertyTests.cs b/tests/Avalonia.Base.UnitTests/AvaloniaPropertyTests.cs
index 181596a681..bde750efdc 100644
--- a/tests/Avalonia.Base.UnitTests/AvaloniaPropertyTests.cs
+++ b/tests/Avalonia.Base.UnitTests/AvaloniaPropertyTests.cs
@@ -2,8 +2,6 @@ using System;
 using System.Collections.Generic;
 using Avalonia.Data;
 using Avalonia.PropertyStore;
-using Avalonia.Styling;
-using Avalonia.Utilities;
 using Xunit;
 
 namespace Avalonia.Base.UnitTests
@@ -29,7 +27,7 @@ namespace Avalonia.Base.UnitTests
         [Fact]
         public void GetMetadata_Returns_Supplied_Value()
         {
-            var metadata = new AvaloniaPropertyMetadata();
+            var metadata = new TestMetadata();
             var target = new TestProperty<string>("test", typeof(Class1), metadata);
 
             Assert.Same(metadata, target.GetMetadata<Class1>());
@@ -38,26 +36,30 @@ namespace Avalonia.Base.UnitTests
         [Fact]
         public void GetMetadata_Returns_Supplied_Value_For_Derived_Class()
         {
-            var metadata = new AvaloniaPropertyMetadata();
+            var metadata = new TestMetadata();
             var target = new TestProperty<string>("test", typeof(Class1), metadata);
 
             Assert.Same(metadata, target.GetMetadata<Class2>());
         }
 
         [Fact]
-        public void GetMetadata_Returns_Supplied_Value_For_Unrelated_Class()
+        public void GetMetadata_Returns_TypeSafe_Metadata_For_Unrelated_Class()
         {
-            var metadata = new AvaloniaPropertyMetadata();
+            var metadata = new TestMetadata(BindingMode.OneWayToSource, true, x => { _ = (StyledElement)x; });
             var target = new TestProperty<string>("test", typeof(Class3), metadata);
 
-            Assert.Same(metadata, target.GetMetadata<Class2>());
+            var targetMetadata = (TestMetadata)target.GetMetadata<Class2>();
+
+            Assert.Equal(metadata.DefaultBindingMode, targetMetadata.DefaultBindingMode);
+            Assert.Equal(metadata.EnableDataValidation, targetMetadata.EnableDataValidation);
+            Assert.Equal(null, targetMetadata.OwnerSpecificAction);
         }
 
         [Fact]
         public void GetMetadata_Returns_Overridden_Value()
         {
-            var metadata = new AvaloniaPropertyMetadata();
-            var overridden = new AvaloniaPropertyMetadata();
+            var metadata = new TestMetadata();
+            var overridden = new TestMetadata();
             var target = new TestProperty<string>("test", typeof(Class1), metadata);
 
             target.OverrideMetadata<Class2>(overridden);
@@ -68,9 +70,9 @@ namespace Avalonia.Base.UnitTests
         [Fact]
         public void OverrideMetadata_Should_Merge_Values()
         {
-            var metadata = new AvaloniaPropertyMetadata(BindingMode.TwoWay);
+            var metadata = new TestMetadata(BindingMode.TwoWay);
             var notify = (Action<AvaloniaObject, bool>)((a, b) => { });
-            var overridden = new AvaloniaPropertyMetadata();
+            var overridden = new TestMetadata();
             var target = new TestProperty<string>("test", typeof(Class1), metadata);
 
             target.OverrideMetadata<Class2>(overridden);
@@ -131,15 +133,31 @@ namespace Avalonia.Base.UnitTests
         [Fact]
         public void PropertyMetadata_BindingMode_Default_Returns_OneWay()
         {
-            var data = new AvaloniaPropertyMetadata(defaultBindingMode: BindingMode.Default);
+            var data = new TestMetadata(defaultBindingMode: BindingMode.Default);
 
             Assert.Equal(BindingMode.OneWay, data.DefaultBindingMode);
         }
 
+        private class TestMetadata : AvaloniaPropertyMetadata
+        {
+            public Action<AvaloniaObject> OwnerSpecificAction { get; }
+
+            public TestMetadata(BindingMode defaultBindingMode = BindingMode.Default, 
+                bool? enableDataValidation = null,
+                Action<AvaloniaObject> ownerSpecificAction = null) 
+                : base(defaultBindingMode, enableDataValidation)
+            {
+                OwnerSpecificAction = ownerSpecificAction;
+            }
+
+            public override AvaloniaPropertyMetadata GenerateTypeSafeMetadata() =>
+                new TestMetadata(DefaultBindingMode, EnableDataValidation, null);
+        }
+
         private class TestProperty<TValue> : AvaloniaProperty<TValue>
         {
-            public TestProperty(string name, Type ownerType, AvaloniaPropertyMetadata metadata = null)
-                : base(name, ownerType, metadata ?? new AvaloniaPropertyMetadata())
+            public TestProperty(string name, Type ownerType, TestMetadata metadata = null)
+                : base(name, ownerType, metadata ?? new TestMetadata())
             {
             }