Drop hint IDropInfoBuilder is used renders incorrect VisualTarget

src/Directory.packages.props

@@ -18,6 +18,7 @@
         <PackageVersion Include="MahApps.Metro.IconPacks.FeatherIcons" Version="5.1.0" />
         <PackageVersion Include="MahApps.Metro.IconPacks.Material" Version="5.1.0" />
         <PackageVersion Include="MahApps.Metro.IconPacks.Octicons" Version="5.1.0" />
+        <PackageVersion Include="Microsoft.Xaml.Behaviors.Wpf" Version="1.1.37" />
         <PackageVersion Include="Faker.Net" Version="2.0.163" />
         <PackageVersion Include="Costura.Fody" Version="6.0.0" />
 

src/GongSolutions.WPF.DragDrop/DragDrop.cs

@@ -735,7 +735,7 @@ private static void OnRealTargetDragLeave(object sender, DragEventArgs e)
                 dropHandler.DragLeave(dropInfo);
                 if(_dragInProgress)
                 {
-                    DropHintHelpers.OnDragLeave(sender, dropHandler, dragInfo);
+                    DropHintHelpers.OnDragLeave(dropHandler, dragInfo, dropInfo);
                 }
             }
 
@@ -782,7 +782,7 @@ private static void DropTargetOnDragOver(object sender, DragEventArgs e, EventTy
             }
 
             dropHandler.DragOver(dropInfo);
-            DropHintHelpers.DragOver(sender, dropInfo);
+            DropHintHelpers.DragOver(dropInfo);
 
             if (dragInfo is not null)
             {

src/GongSolutions.WPF.DragDrop/DropHintHelpers.cs

@@ -76,10 +76,10 @@ public static void OnDropFinished()
         /// </summary>
         /// <param name="dropHandler">The <see cref="IDropTarget"/> for the operation</param>
         /// <param name="dragInfo">The <see cref="IDragInfo"/> initiating the drag</param>
-        /// <param name="sender">The target element of the drag</param>
-        public static void OnDragLeave(object sender, IDropTarget dropHandler, IDragInfo dragInfo)
+        /// <param name="dropInfo">Drop info containing with target.</param>
+        public static void OnDragLeave(IDropTarget dropHandler, IDragInfo dragInfo, IDropInfo dropInfo)
         {
-            var wrapper = _dropTargetHintReferences.Find(m => m.Target == sender);
+            var wrapper = _dropTargetHintReferences.Find(m => m.Target == dropInfo.VisualTarget);
             if (wrapper != null)
             {
                 var dropHintInfo = new DropHintInfo(dragInfo);
@@ -92,10 +92,9 @@ public static void OnDragLeave(object sender, IDropTarget dropHandler, IDragInfo
         /// Update drop hint for the current element.
         /// </summary>
         /// <param name="dropInfo"></param>
-        /// <param name="sender"></param>
-        public static void DragOver(object sender, IDropInfo dropInfo)
+        public static void DragOver(IDropInfo dropInfo)
         {
-            var wrapper = _dropTargetHintReferences.Find(m => m.Target == sender);
+            var wrapper = _dropTargetHintReferences.Find(m => m.Target == dropInfo.VisualTarget);
             if (wrapper != null)
             {
                 UpdateHintAdorner(wrapper, dropInfo.DropTargetHintAdorner, new DropHintData(dropInfo.DropTargetHintState, dropInfo.DropHintText));

src/Showcase/Models/ComboBoxDropBehavior.cs

@@ -0,0 +1,36 @@
+namespace Showcase.WPF.DragDrop.Models;
+
+using System.Windows;
+using System.Windows.Controls;
+using Microsoft.Xaml.Behaviors;
+using DragDrop = GongSolutions.Wpf.DragDrop.DragDrop;
+
+public class ComboBoxDropBehavior : Behavior<ComboBox>
+{
+    protected override void OnAttached()
+    {
+        base.OnAttached();
+        AssociatedObject.Loaded += AssociatedObject_Loaded;
+    }
+
+    protected override void OnDetaching()
+    {
+        base.OnDetaching();
+        AssociatedObject.Loaded -= AssociatedObject_Loaded;
+    }
+
+    private void AssociatedObject_Loaded(object sender, RoutedEventArgs e)
+    {
+        if (AssociatedObject.Template.FindName("PART_EditableTextBox", AssociatedObject) is not TextBox textBox)
+        {
+            return;
+        }
+
+        // Create and set the custom drop info builder
+        var dropInfoBuilder = new ComboBoxDropInfoBuilder(AssociatedObject);
+        DragDrop.SetDropInfoBuilder(textBox, dropInfoBuilder);
+
+        // Attach Gong DragDrop manually
+        DragDrop.SetIsDropTarget(textBox, DragDrop.GetIsDropTarget(AssociatedObject));
+    }
+}

src/Showcase/Models/ComboBoxDropHandler.cs

@@ -0,0 +1,71 @@
+namespace Showcase.WPF.DragDrop.Models;
+
+using System.Windows;
+using System.Windows.Controls;
+using GongSolutions.Wpf.DragDrop;
+
+public class ComboBoxDropHandler : IDropTarget
+{
+    public void DragEnter(IDropInfo dropInfo)
+    {
+        // nothing here
+    }
+
+    public void DragLeave(IDropInfo dropInfo)
+    {
+        // nothing here
+    }
+
+    private bool IsAcceptedItem(IDragInfo data)
+    {
+        return data?.Data is ListBoxItem;
+    }
+
+    public void DropHint(IDropHintInfo dropHintInfo)
+    {
+        if (!IsAcceptedItem(dropHintInfo.DragInfo))
+        {
+            if (dropHintInfo.DragInfo == null)
+            {
+                return;
+            }
+
+            dropHintInfo.DropHintText = "Cannot drop here";
+            dropHintInfo.DropTargetHintAdorner = DropTargetAdorners.Hint;
+            dropHintInfo.DropTargetHintState = DropHintState.Error;
+            return;
+        }
+
+        dropHintInfo.DropHintText = "Drop here";
+        dropHintInfo.DropTargetHintAdorner = DropTargetAdorners.Hint;
+    }
+
+    public void DragOver(IDropInfo dropInfo)
+    {
+        if (!IsAcceptedItem(dropInfo.DragInfo))
+        {
+            if (dropInfo.DragInfo == null)
+            {
+                return;
+            }
+
+            dropInfo.DropHintText = "Cannot drop here";
+            dropInfo.DropTargetHintAdorner = DropTargetAdorners.Hint;
+            dropInfo.DropTargetHintState = DropHintState.Error;
+            return;
+        }
+
+        dropInfo.DropHintText = "Let go!";
+        dropInfo.DropTargetHintState = DropHintState.Active;
+        dropInfo.DropTargetHintAdorner = DropTargetAdorners.Hint;
+        dropInfo.Effects = DragDropEffects.Copy;
+        dropInfo.EffectText = "drop";
+        dropInfo.DestinationText = "Drop";
+    }
+
+    public void Drop(IDropInfo dropInfo)
+    {
+        dropInfo.DropTargetAdorner = DropTargetAdorners.Hint;
+        dropInfo.Effects = DragDropEffects.Copy;
+    }
+}

src/Showcase/Models/ComboBoxDropInfoBuilder.cs

@@ -0,0 +1,33 @@
+namespace Showcase.WPF.DragDrop.Models;
+
+using System.Windows;
+using System.Windows.Controls;
+using GongSolutions.Wpf.DragDrop;
+using GongSolutions.Wpf.DragDrop.Utilities;
+
+/// <summary>
+/// Drop info builder for ComboBox to redirect drop information to the ComboBox itself instead
+/// of the internal TextBox.
+/// </summary>
+/// <param name="comboBox"></param>
+public class ComboBoxDropInfoBuilder(ComboBox comboBox) : IDropInfoBuilder
+{
+    public IDropInfo CreateDropInfo(object sender, DragEventArgs e, IDragInfo dragInfo, EventType eventType)
+    {
+        if (!comboBox.IsEditable)
+        {
+            return null;
+        }
+
+        // If the target is the TextBox inside ComboBox, we want to create
+        // drop info as if the drop happened on the ComboBox itself
+        if (e.Source is TextBox || (e.Source is UIElement element && element.GetVisualAncestor<TextBox>() != null))
+        {
+            e.Source = comboBox;
+            e.Handled = true;
+            return new DropInfo(comboBox, e, dragInfo, eventType);
+        }
+
+        return null;
+    }
+}

src/Showcase/Showcase.WPF.DragDrop.csproj

@@ -22,6 +22,7 @@
     </ItemGroup>
 
     <ItemGroup>
+        <PackageReference Include="Microsoft.Xaml.Behaviors.Wpf" />
         <PackageReference Include="MahApps.Metro.IconPacks.FeatherIcons" />
         <PackageReference Include="MahApps.Metro.IconPacks.Material" />
         <PackageReference Include="MahApps.Metro.IconPacks.Octicons" />

src/Showcase/Views/Issues.xaml

@@ -8,6 +8,7 @@
              xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
              xmlns:models="clr-namespace:Showcase.WPF.DragDrop.Models"
              xmlns:viewModels="clr-namespace:Showcase.WPF.DragDrop.ViewModels"
+             xmlns:b="http://schemas.microsoft.com/xaml/behaviors"
              d:DataContext="{d:DesignInstance viewModels:MainViewModel}"
              d:DesignHeight="400"
              d:DesignWidth="600"
@@ -1248,6 +1249,94 @@
                 </DockPanel>
             </TabItem>
 
+            <TabItem Header="#519">
+                <TabItem.Resources>
+                    <models:ComboBoxDropHandler x:Key="ComboBoxDropHandler"/>
+                    <DataTemplate x:Key="DefaultDropHintTemplate" DataType="{x:Type dd:DropHintData}">
+                        <Border x:Name="RootBorder"
+                                Background="#008000"
+                                BorderBrush="#008000"
+                                BorderThickness="1"
+                                CornerRadius="5">
+                            <TextBlock HorizontalAlignment="Center"
+                                       VerticalAlignment="Center"
+                                       Foreground="White"
+                                       Text="{Binding HintText}"
+                                       TextWrapping="Wrap" />
+                        </Border>
+                        <DataTemplate.Triggers>
+                            <DataTrigger Binding="{Binding Path=HintState}" Value="Active">
+                                <Setter TargetName="RootBorder" Property="Background" Value="#263B80" />
+                            </DataTrigger>
+                            <DataTrigger Binding="{Binding Path=HintState}" Value="Error">
+                                <Setter TargetName="RootBorder" Property="Background" Value="#8B0000" />
+                            </DataTrigger>
+                        </DataTemplate.Triggers>
+                    </DataTemplate>
+                </TabItem.Resources>
+                <DockPanel LastChildFill="True">
+                    <Grid DockPanel.Dock="Top">
+                        <TextBlock Style="{StaticResource SampleHeaderTextBlockStyle}" Text="Drop hint not available for TextBox part of ComboBox when IsEditable=true." />
+                        <Button CommandParameter="519"
+                                Style="{StaticResource GitHubPullRequestButtonStyle}"
+                                ToolTip="Open #519 on Github" />
+                    </Grid>
+                    <ScrollViewer HorizontalScrollBarVisibility="Disabled" VerticalScrollBarVisibility="Auto">
+                        <StackPanel>
+
+                            <UniformGrid Columns="3">
+                                <TextBlock Text="#1 allows drop only on glyph" TextWrapping="Wrap"/>
+                                <TextBlock Text="#2 allows on whole (behavior)" TextWrapping="Wrap"/>
+                                <TextBlock Text="#3 allows on whole " TextWrapping="Wrap"/>
+                                <ComboBox IsEditable="True"
+                                          Text="IsEditable"
+                                          Margin="2"
+                                          Width="150"
+                                          dd:DragDrop.IsDropTarget="True"
+                                          dd:DragDrop.DropHandler="{StaticResource ComboBoxDropHandler}"
+                                          dd:DragDrop.UseDropTargetHint="True"
+                                          dd:DragDrop.DropHintDataTemplate="{StaticResource DefaultDropHintTemplate}"
+                                />
+                                <ComboBox IsEditable="True"
+                                          Text="IsEditable Behavior"
+                                          Margin="2"
+                                          Width="150"
+                                          dd:DragDrop.IsDropTarget="True"
+                                          dd:DragDrop.DropHandler="{StaticResource ComboBoxDropHandler}"
+                                          dd:DragDrop.UseDropTargetHint="True"
+                                          dd:DragDrop.DropHintDataTemplate="{StaticResource DefaultDropHintTemplate}">
+                                    <b:Interaction.Behaviors>
+                                        <models:ComboBoxDropBehavior />
+                                    </b:Interaction.Behaviors>
+                                </ComboBox>
+                                <ComboBox IsEditable="False"
+                                          Text="IsEditable False"
+                                          Margin="2"
+                                          Width="150"
+                                          dd:DragDrop.IsDropTarget="True"
+                                          dd:DragDrop.DropHandler="{StaticResource ComboBoxDropHandler}"
+                                          dd:DragDrop.UseDropTargetHint="True"
+                                          dd:DragDrop.DropHintDataTemplate="{StaticResource DefaultDropHintTemplate}"
+                                />
+                            </UniformGrid>
+                            <Grid>
+                                <Grid.ColumnDefinitions>
+                                    <ColumnDefinition Width="Auto" />
+                                </Grid.ColumnDefinitions>
+
+                                <ListBox MinWidth="200"
+                                         dd:DragDrop.IsDragSource="True">
+                                    <ListBoxItem Content="Item 1" />
+                                    <ListBoxItem Content="Item 2" />
+                                    <ListBoxItem Content="Item 3" />
+                                    <ListBoxItem Content="Item 4" />
+                                    <ListBoxItem Content="Item 5" />
+                                </ListBox>
+                            </Grid>
+                        </StackPanel>
+                    </ScrollViewer>
+                </DockPanel>
+            </TabItem>
         </TabControl>
 
     </Grid>