feat: ComboBox.OnDropDownOpened/Closed

Author: MartinZikmund

src/Uno.UI/Generated/3.0.0.0/Windows.UI.Xaml.Controls/ComboBox.cs

@@ -242,14 +242,14 @@ public  object Description
 		// Forced skipping of method Windows.UI.Xaml.Controls.ComboBox.Description.set
 		// Forced skipping of method Windows.UI.Xaml.Controls.ComboBox.TextSubmitted.add
 		// Forced skipping of method Windows.UI.Xaml.Controls.ComboBox.TextSubmitted.remove
-		#if __ANDROID__ || __IOS__ || NET461 || __WASM__ || __SKIA__ || __NETSTD_REFERENCE__ || __MACOS__
+		#if false
 		[global::Uno.NotImplemented("__ANDROID__", "__IOS__", "NET461", "__WASM__", "__SKIA__", "__NETSTD_REFERENCE__", "__MACOS__")]
 		protected virtual void OnDropDownClosed( object e)
 		{
 			global::Windows.Foundation.Metadata.ApiInformation.TryRaiseNotImplemented("Windows.UI.Xaml.Controls.ComboBox", "void ComboBox.OnDropDownClosed(object e)");
 		}
 		#endif
-		#if __ANDROID__ || __IOS__ || NET461 || __WASM__ || __SKIA__ || __NETSTD_REFERENCE__ || __MACOS__
+		#if false
 		[global::Uno.NotImplemented("__ANDROID__", "__IOS__", "NET461", "__WASM__", "__SKIA__", "__NETSTD_REFERENCE__", "__MACOS__")]
 		protected virtual void OnDropDownOpened( object e)
 		{

src/Uno.UI/UI/Xaml/Controls/ComboBox/ComboBox.cs

@@ -165,6 +165,16 @@ private protected override void OnUnloaded()
 			Xaml.Window.Current.SizeChanged -= OnWindowSizeChanged;
 		}
 
+		protected virtual void OnDropDownClosed(object e)
+		{
+			DropDownClosed?.Invoke(this, null!);
+		}
+
+		protected virtual void OnDropDownOpened(object e)
+		{
+			DropDownOpened?.Invoke(this, null!);
+		}
+
 		private void OnWindowSizeChanged(object sender, Windows.UI.Core.WindowSizeChangedEventArgs e)
 		{
 			IsDropDownOpen = false;
@@ -370,9 +380,10 @@ partial void OnIsDropDownOpenChangedPartial(bool oldIsDropDownOpen, bool newIsDr
 				_popup.IsOpen = newIsDropDownOpen;
 			}
 
+			var args = new RoutedEventArgs() { OriginalSource = this };
 			if (newIsDropDownOpen)
 			{
-				DropDownOpened?.Invoke(this, newIsDropDownOpen);
+				OnDropDownOpened(args);
 
 				RestoreSelectedItem();
 
@@ -383,8 +394,11 @@ partial void OnIsDropDownOpenChangedPartial(bool oldIsDropDownOpen, bool newIsDr
 			}
 			else
 			{
-				DropDownClosed?.Invoke(this, newIsDropDownOpen);
+				OnDropDownClosed(args);
 				UpdateContentPresenter();
+
+				// Focus moves to ComboBox after item is selected.
+				Focus(FocusState.Programmatic);
 			}
 
 			UpdateDropDownState();