Preview 3: Complete control implementation with XAML data binding

Major milestone adding full control functionality:

Controls Enhanced:
- Entry/Editor: Full keyboard input, cursor navigation, selection, clipboard
- CollectionView: Data binding, selection highlighting, scrolling
- CheckBox/Switch/Slider: Interactive state management
- Picker/DatePicker/TimePicker: Dropdown selection with popup overlays
- ProgressBar/ActivityIndicator: Animated progress display
- Button: Press/release visual states
- Border/Frame: Rounded corners, stroke styling
- Label: Text wrapping, alignment, decorations
- Grid/StackLayout: Margin and padding support

Features Added:
- DisplayAlert dialogs with button actions
- NavigationPage with toolbar and back navigation
- Shell with flyout menu navigation
- XAML value converters for data binding
- Margin support in all layout containers
- Popup overlay system for pickers

New Samples:
- TodoApp: Full CRUD task manager with NavigationPage
- ShellDemo: Comprehensive control showcase

Removed:
- ControlGallery (replaced by ShellDemo)
- LinuxDemo (replaced by TodoApp)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Handlers/PickerHandler.cs

@@ -6,6 +6,7 @@ using Microsoft.Maui.Graphics;
 using Microsoft.Maui.Controls;
 using Microsoft.Maui.Platform;
 using SkiaSharp;
+using System.Collections.Specialized;
 
 namespace Microsoft.Maui.Platform.Linux.Handlers;
 
@@ -25,6 +26,7 @@ public partial class PickerHandler : ViewHandler<IPicker, SkiaPicker>
             [nameof(IPicker.HorizontalTextAlignment)] = MapHorizontalTextAlignment,
             [nameof(IPicker.VerticalTextAlignment)] = MapVerticalTextAlignment,
             [nameof(IView.Background)] = MapBackground,
+            [nameof(Picker.ItemsSource)] = MapItemsSource,
         };
 
     public static CommandMapper<IPicker, PickerHandler> CommandMapper =
@@ -32,6 +34,8 @@ public partial class PickerHandler : ViewHandler<IPicker, SkiaPicker>
         {
         };
 
+    private INotifyCollectionChanged? _itemsCollection;
+
     public PickerHandler() : base(Mapper, CommandMapper)
     {
     }
@@ -51,6 +55,13 @@ public partial class PickerHandler : ViewHandler<IPicker, SkiaPicker>
         base.ConnectHandler(platformView);
         platformView.SelectedIndexChanged += OnSelectedIndexChanged;
 
+        // Subscribe to items collection changes
+        if (VirtualView is Picker picker && picker.Items is INotifyCollectionChanged items)
+        {
+            _itemsCollection = items;
+            _itemsCollection.CollectionChanged += OnItemsCollectionChanged;
+        }
+
         // Load items
         ReloadItems();
     }
@@ -58,9 +69,21 @@ public partial class PickerHandler : ViewHandler<IPicker, SkiaPicker>
     protected override void DisconnectHandler(SkiaPicker platformView)
     {
         platformView.SelectedIndexChanged -= OnSelectedIndexChanged;
+
+        if (_itemsCollection != null)
+        {
+            _itemsCollection.CollectionChanged -= OnItemsCollectionChanged;
+            _itemsCollection = null;
+        }
+
         base.DisconnectHandler(platformView);
     }
 
+    private void OnItemsCollectionChanged(object? sender, NotifyCollectionChangedEventArgs e)
+    {
+        ReloadItems();
+    }
+
     private void OnSelectedIndexChanged(object? sender, EventArgs e)
     {
         if (VirtualView is null || PlatformView is null) return;
@@ -130,4 +153,9 @@ public partial class PickerHandler : ViewHandler<IPicker, SkiaPicker>
             handler.PlatformView.BackgroundColor = solidPaint.Color.ToSKColor();
         }
     }
+
+    public static void MapItemsSource(PickerHandler handler, IPicker picker)
+    {
+        handler.ReloadItems();
+    }
 }