src/AdvancedCalculator/ViewModels/MainViewModel.cs

@@ -35,10 +35,6 @@ public partial class MainViewModel : ViewModelBase
     [ObservableProperty]
     private int _selectedHistoryIndex = -1;
 
-    // Caret position in the input TextBox
-    [ObservableProperty]
-    private int _caretIndex;
-
     public ObservableCollection<HistoryItem> History { get; }
     public ObservableCollection<VariableItem> Variables { get; }
 
@@ -65,11 +61,6 @@ public partial class MainViewModel : ViewModelBase
         if (string.IsNullOrWhiteSpace(functionDefintionItem.FunctionName))
             return;
         InsertToken(functionDefintionItem.FunctionName + "()");
-        // Place caret inside the parentheses
-        if (!string.IsNullOrEmpty(InputText))
-        {
-            CaretIndex = Math.Max(0, InputText.Length - 1);
-        }
         // Close the functions flyout after insertion for smoother UX
         IsFunctionsPanelOpen = false;
     }

src/AdvancedCalculator/Views/MainView.axaml

@@ -136,7 +136,9 @@
             <Button.Flyout>
                 <Flyout 
                         IsOpen="{Binding IsFunctionsPanelOpen, Mode=TwoWay}"
-                        Placement="BottomEdgeAlignedLeft">
+                        Placement="BottomEdgeAlignedLeft"
+                        Opened="OnFunctionsFlyoutOpened"
+                        Closed="OnFunctionsFlyoutClosed">
                     <Border x:Name="FunctionsPanelRoot" Padding="8" MinWidth="360" MaxHeight="420"
                             Background="{DynamicResource Brush.Surface}" BorderBrush="{DynamicResource Brush.Border}" BorderThickness="1" CornerRadius="6">
                         <ScrollViewer>
@@ -183,9 +185,7 @@
             <TextBlock FontFamily="{StaticResource MDI}" Text="{x:Static m:IconFont.Function}" />
         </Button>
 
-                    <TextBox x:Name="InputBox" Grid.Column="2" Text="{Binding InputText, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
+                    <TextBox Grid.Column="2" Text="{Binding InputText, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" MinHeight="44"
-                             CaretIndex="{Binding CaretIndex, Mode=TwoWay}"
-                             MinHeight="44"
                              AutomationProperties.Name="Expression input"
                              Watermark="Type an expression (e.g., 2 + 2)">
                         <InputElement.KeyBindings>

src/AdvancedCalculator/Views/MainView.axaml.cs

@@ -21,7 +21,7 @@ public partial class MainView : UserControl
 
     private MainViewModel? _vm;
     private ListBox? _historyList;
-    // Functions flyout is handled via per-item Tapped in XAML
+    private Border? _functionsPanelRoot;
 
     private void OnAttachedToVisualTree(object? sender, VisualTreeAttachmentEventArgs e)
     {
@@ -53,6 +53,12 @@ public partial class MainView : UserControl
             _historyList.RemoveHandler(InputElement.TappedEvent, OnHistoryTapped);
             _historyList = null;
         }
+        // Detach functions panel tap handler if still attached
+        if (_functionsPanelRoot is not null)
+        {
+            _functionsPanelRoot.RemoveHandler(InputElement.TappedEvent, OnFunctionsItemTapped);
+            _functionsPanelRoot = null;
+        }
         _vm = null;
     }
 
@@ -94,12 +100,27 @@ public partial class MainView : UserControl
             _vm?.InsertFunctionCommand.CanExecute(item) == true)
         {
             _vm.InsertFunctionCommand.Execute(item);
-            // Return focus to the input box so the caret is active
-            var input = this.FindControl<TextBox>("InputBox");
-            input?.Focus();
             e.Handled = true;
         }
     }
 
-    // Removed Opened/Closed dynamic wiring; handled directly in XAML.
+
+    private void OnFunctionsFlyoutOpened(object? sender, EventArgs e)
+{
+    if (sender is Flyout flyout && sender is ContentPresenter presenter)
+    {
+        _functionsPanelRoot = presenter.FindControl<Border>("FunctionsPanelRoot");
+        _functionsPanelRoot?.AddHandler(InputElement.TappedEvent, OnFunctionsItemTapped,
+            RoutingStrategies.Tunnel | RoutingStrategies.Bubble);
+    }
+}
+
+    private void OnFunctionsFlyoutClosed(object? sender, EventArgs e)
+    {
+        if (_functionsPanelRoot is not null)
+        {
+            _functionsPanelRoot.RemoveHandler(InputElement.TappedEvent, OnFunctionsItemTapped);
+            _functionsPanelRoot = null;
+        }
+    }
 }