Merge pull request #3659 from Deadpikle/feature/textbox-fix-right-click

Adjusted TextBox right-click behavior

src/Avalonia.Controls/TextBox.cs

@@ -683,12 +683,12 @@ namespace Avalonia.Controls
 
         protected override void OnPointerPressed(PointerPressedEventArgs e)
         {
-            var point = e.GetPosition(_presenter);
-            var index = CaretIndex = _presenter.GetCaretIndex(point);
             var text = Text;
 
-            if (text != null && e.MouseButton == MouseButton.Left)
+            if (text != null && e.GetCurrentPoint(this).Properties.IsLeftButtonPressed)
             {
+                var point = e.GetPosition(_presenter);
+                var index = CaretIndex = _presenter.GetCaretIndex(point);
                 switch (e.ClickCount)
                 {
                     case 1:
@@ -714,7 +714,8 @@ namespace Avalonia.Controls
 
         protected override void OnPointerMoved(PointerEventArgs e)
         {
-            if (_presenter != null && e.Pointer.Captured == _presenter)
+            // selection should not change during pointer move if the user right clicks
+            if (_presenter != null && e.Pointer.Captured == _presenter && e.GetCurrentPoint(this).Properties.IsLeftButtonPressed)
             {
                 var point = e.GetPosition(_presenter);
 
@@ -727,6 +728,22 @@ namespace Avalonia.Controls
         {
             if (_presenter != null && e.Pointer.Captured == _presenter)
             {
+                if (e.InitialPressMouseButton == MouseButton.Right)
+                {
+                    var point = e.GetPosition(_presenter);
+                    var caretIndex = _presenter.GetCaretIndex(point);
+
+                    // see if mouse clicked inside current selection
+                    // if it did not, we change the selection to where the user clicked
+                    var firstSelection = Math.Min(SelectionStart, SelectionEnd);
+                    var lastSelection = Math.Max(SelectionStart, SelectionEnd);
+                    var didClickInSelection = SelectionStart != SelectionEnd && 
+                        caretIndex >= firstSelection && caretIndex <= lastSelection;
+                    if (!didClickInSelection)
+                    {
+                        CaretIndex = SelectionEnd = SelectionStart = caretIndex;
+                    }
+                }
                 e.Pointer.Capture(null);
             }
         }