Merge pull request #19318 from ramezgerges/textbox_selection_shift_tap

fix(textbox): extend selection when on tapping when shift is held

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml_Controls/Given_TextBox.skia.cs

@@ -935,6 +935,45 @@ public async Task When_Pointer_Tap()
 			Assert.AreEqual(0, SUT.SelectionLength);
 		}
 
+		[TestMethod]
+		public async Task When_Pointer_Shift_Tap()
+		{
+			using var _ = new TextBoxFeatureConfigDisposable();
+
+			var SUT = new TextBox
+			{
+				Width = 130,
+				Text = "Hello world",
+			};
+
+			WindowHelper.WindowContent = SUT;
+
+			await WindowHelper.WaitForIdle();
+			await WindowHelper.WaitForLoaded(SUT);
+
+			SUT.Focus(FocusState.Programmatic);
+			await WindowHelper.WaitForIdle();
+
+			var injector = InputInjector.TryCreate() ?? throw new InvalidOperationException("Failed to init the InputInjector");
+			using var mouse = injector.GetMouse();
+
+			mouse.MoveTo(SUT.GetAbsoluteBounds().GetCenter());
+			await WindowHelper.WaitForIdle();
+
+			mouse.Press();
+			mouse.Release();
+			await WindowHelper.WaitForIdle();
+
+			var selectionEnd = SUT.SelectionStart;
+
+			mouse.MoveBy(-20, 0);
+			mouse.Press(VirtualKeyModifiers.Shift);
+			mouse.Release(VirtualKeyModifiers.Shift);
+			await WindowHelper.WaitForIdle();
+
+			Assert.AreEqual(selectionEnd, SUT.SelectionStart + SUT.SelectionLength);
+		}
+
 		[TestMethod]
 		public async Task When_Pointer_RightClick_No_Selection()
 		{

src/Uno.UI/UI/Xaml/Controls/TextBox/TextBox.pointers.skia.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Diagnostics;
 using Windows.Foundation;
+using Windows.System;
 using Microsoft.UI.Xaml.Input;
 using Uno.Extensions;
 using Uno.UI.Helpers.WinUI;
@@ -163,7 +164,15 @@ partial void OnPointerPressedPartial(PointerRoutedEventArgs args)
 			{
 				// single click
 				CaretMode = CaretDisplayMode.ThumblessCaretShowing;
-				Select(index, 0);
+				if ((args.KeyModifiers & VirtualKeyModifiers.Shift) != 0)
+				{
+					var selectionInternalStart = _selection.selectionEndsAtTheStart ? _selection.start + _selection.length : _selection.start;
+					SelectInternal(selectionInternalStart, index - selectionInternalStart);
+				}
+				else
+				{
+					Select(index, 0);
+				}
 				_lastPointerDown = (currentPoint, 0);
 			}
 		}