From 8032f82934445eb90d732184a416a48f32fedbaf Mon Sep 17 00:00:00 2001
From: Kevin Sommer <kevin@pasoma.de>
Date: Thu, 3 Oct 2024 12:13:52 +0200
Subject: [PATCH] Check if expected format is available

---
 .../ContextDropBehavior.cs                    | 34 ++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

diff --git a/src/Avalonia.Xaml.Interactions.DragAndDrop/ContextDropBehavior.cs b/src/Avalonia.Xaml.Interactions.DragAndDrop/ContextDropBehavior.cs
index 8d689edb..e16d6f9d 100644
--- a/src/Avalonia.Xaml.Interactions.DragAndDrop/ContextDropBehavior.cs
+++ b/src/Avalonia.Xaml.Interactions.DragAndDrop/ContextDropBehavior.cs
@@ -1,4 +1,5 @@
-using Avalonia.Controls;
+using System.Linq;
+using Avalonia.Controls;
 using Avalonia.Input;
 using Avalonia.Interactivity;
 using Avalonia.Xaml.Interactivity;
@@ -52,6 +53,7 @@ protected override void OnAttachedToVisualTree()
         {
             DragDrop.SetAllowDrop(AssociatedObject, true);
         }
+
         AssociatedObject?.AddHandler(DragDrop.DragEnterEvent, DragEnter);
         AssociatedObject?.AddHandler(DragDrop.DragLeaveEvent, DragLeave);
         AssociatedObject?.AddHandler(DragDrop.DragOverEvent, DragOver);
@@ -65,6 +67,7 @@ protected override void OnDetachedFromVisualTree()
         {
             DragDrop.SetAllowDrop(AssociatedObject, false);
         }
+
         AssociatedObject?.RemoveHandler(DragDrop.DragEnterEvent, DragEnter);
         AssociatedObject?.RemoveHandler(DragDrop.DragLeaveEvent, DragLeave);
         AssociatedObject?.RemoveHandler(DragDrop.DragOverEvent, DragOver);
@@ -73,6 +76,11 @@ protected override void OnDetachedFromVisualTree()
 
     private void DragEnter(object? sender, DragEventArgs e)
     {
+        if (!IsExpectedFormatAvailable(e))
+        {
+            return;
+        }
+
         var sourceContext = e.Data.Get(ContextDropBehavior.DataFormat);
         var targetContext = Context ?? AssociatedObject?.DataContext;
         Handler?.Enter(sender, e, sourceContext, targetContext);
@@ -85,6 +93,11 @@ private void DragLeave(object? sender, RoutedEventArgs e)
 
     private void DragOver(object? sender, DragEventArgs e)
     {
+        if (!IsExpectedFormatAvailable(e))
+        {
+            return;
+        }
+
         var sourceContext = e.Data.Get(ContextDropBehavior.DataFormat);
         var targetContext = Context ?? AssociatedObject?.DataContext;
         Handler?.Over(sender, e, sourceContext, targetContext);
@@ -92,8 +105,27 @@ private void DragOver(object? sender, DragEventArgs e)
 
     private void Drop(object? sender, DragEventArgs e)
     {
+        if (!IsExpectedFormatAvailable(e))
+        {
+            return;
+        }
+        
         var sourceContext = e.Data.Get(ContextDropBehavior.DataFormat);
         var targetContext = Context ?? AssociatedObject?.DataContext;
         Handler?.Drop(sender, e, sourceContext, targetContext);
     }
+
+
+    private static bool IsExpectedFormatAvailable(DragEventArgs e)
+    {
+        var availableFormats = e.Data.GetDataFormats();
+        if (availableFormats.Contains(ContextDropBehavior.DataFormat))
+        {
+            return true;
+        }
+
+        e.Handled = true;
+        e.DragEffects = DragDropEffects.None;
+        return false;
+    }
 }