Merge pull request #4526 from AvaloniaUI/fixes/textbox-caret-index-lost-on-focus-lost

Fixes/textbox caret index lost on focus lost

src/Avalonia.Controls/TextBox.cs

@@ -369,6 +369,14 @@ namespace Avalonia.Controls
             get { return _newLine; }
             set { SetAndRaise(NewLineProperty, ref _newLine, value); }
         }
+        
+        /// <summary>
+        /// Clears the current selection, maintaining the <see cref="CaretIndex"/>
+        /// </summary>
+        public void ClearSelection()
+        {
+            SelectionStart = SelectionEnd = CaretIndex;
+        }
 
         protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
         {
@@ -413,8 +421,7 @@ namespace Avalonia.Controls
 
             if (ContextMenu == null || !ContextMenu.IsOpen)
             {
-                SelectionStart = 0;
-                SelectionEnd = 0;
+                ClearSelection();
                 RevealPassword = false;
             }
             
@@ -444,7 +451,7 @@ namespace Avalonia.Controls
                     text = Text ?? string.Empty;
                     SetTextInternal(text.Substring(0, caretIndex) + input + text.Substring(caretIndex));
                     CaretIndex += input.Length;
-                    SelectionStart = SelectionEnd = CaretIndex;
+                    ClearSelection();
                     _undoRedoHelper.DiscardRedo();
                 }
             }
@@ -662,7 +669,7 @@ namespace Avalonia.Controls
                             SetTextInternal(text.Substring(0, caretIndex - removedCharacters) +
                                             text.Substring(caretIndex));
                             CaretIndex -= removedCharacters;
-                            SelectionStart = SelectionEnd = CaretIndex;
+                            ClearSelection();
                         }
                         _undoRedoHelper.Snapshot();
 
@@ -735,7 +742,7 @@ namespace Avalonia.Controls
             }
             else if (movement)
             {
-                SelectionStart = SelectionEnd = CaretIndex;
+                ClearSelection();
             }
 
             if (handled || movement)
@@ -1042,7 +1049,8 @@ namespace Avalonia.Controls
                     var end = Math.Max(selectionStart, selectionEnd);
                     var text = Text;
                     SetTextInternal(text.Substring(0, start) + text.Substring(end));
-                    SelectionStart = SelectionEnd = CaretIndex = start;
+                    CaretIndex = start;
+                    ClearSelection();
                     return true;
                 }
                 else
@@ -1131,7 +1139,8 @@ namespace Avalonia.Controls
             set
             {
                 Text = value.Text;
-                SelectionStart = SelectionEnd = CaretIndex = value.CaretPosition;
+                CaretIndex = value.CaretPosition;
+                ClearSelection();
             }
         }
     }

tests/Avalonia.Controls.UnitTests/TextBoxTests.cs

@@ -562,6 +562,41 @@ namespace Avalonia.Controls.UnitTests
             }
         }
         
+        [Fact]
+        public void TextBox_CaretIndex_Persists_When_Focus_Lost()
+        {
+            using (UnitTestApplication.Start(FocusServices))
+            {
+                var target1 = new TextBox
+                {
+                    Template = CreateTemplate(),
+                    Text = "1234"
+                };
+                var target2 = new TextBox
+                {
+                    Template = CreateTemplate(),
+                    Text = "5678"
+                };
+                var sp = new StackPanel();
+                sp.Children.Add(target1);
+                sp.Children.Add(target2);
+
+                target1.ApplyTemplate();
+                target2.ApplyTemplate();
+                
+                var root = new TestRoot { Child = sp };
+
+                target2.Focus();
+                target2.CaretIndex = 2;
+                Assert.False(target1.IsFocused);
+                Assert.True(target2.IsFocused);
+
+                target1.Focus();
+                
+                Assert.Equal(2, target2.CaretIndex);
+            }
+        }
+        
         [Fact]
         public void TextBox_Reveal_Password_Reset_When_Lost_Focus()
         {