Merge pull request #505 from punker76/fix/typo

Typo Detatch -> Detach in DropTargetAdorner corrected

Author: punker76

src/GongSolutions.WPF.DragDrop/DragDrop.cs

@@ -470,8 +470,8 @@ private static void DragSourceDown(object sender, DragInfo dragInfo, InputEventA
                 return;
             }
 
-            // If the sender is a list box that allows multiple selections, ensure that clicking on an 
-            // already selected item does not change the selection, otherwise dragging multiple items 
+            // If the sender is a list box that allows multiple selections, ensure that clicking on an
+            // already selected item does not change the selection, otherwise dragging multiple items
             // is made impossible.
             if ((Keyboard.Modifiers & ModifierKeys.Shift) == 0
                 //&& (Keyboard.Modifiers & ModifierKeys.Control) == 0 // #432
@@ -783,7 +783,7 @@ private static void DropTargetOnDragOver(object sender, DragEventArgs e, EventTy
             // If the target is an ItemsControl then update the drop target adorner.
             if (itemsControl != null)
             {
-                // Display the adorner in the control's ItemsPresenter. If there is no 
+                // Display the adorner in the control's ItemsPresenter. If there is no
                 // ItemsPresenter provided by the style, try getting hold of a
                 // ScrollContentPresenter and using that.
                 UIElement adornedElement;
@@ -1001,7 +1001,7 @@ private static DropTargetAdorner DropTargetAdorner
             get => dropTargetAdorner;
             set
             {
-                dropTargetAdorner?.Detatch();
+                dropTargetAdorner?.Detach();
                 dropTargetAdorner = value;
             }
         }

src/GongSolutions.WPF.DragDrop/DropTargetAdorner.cs

@@ -5,6 +5,8 @@
 
 namespace GongSolutions.Wpf.DragDrop
 {
+    using JetBrains.Annotations;
+
     public abstract class DropTargetAdorner : Adorner
     {
         public DropTargetAdorner(UIElement adornedElement, IDropInfo dropInfo)
@@ -14,8 +16,9 @@ public DropTargetAdorner(UIElement adornedElement, IDropInfo dropInfo)
             this.IsHitTestVisible = false;
             this.AllowDrop = false;
             this.SnapsToDevicePixels = true;
-            this.m_AdornerLayer = AdornerLayer.GetAdornerLayer(adornedElement);
-            this.m_AdornerLayer.Add(this);
+            this.adornerLayer = AdornerLayer.GetAdornerLayer(adornedElement);
+            // can be null but should normally not be null
+            this.adornerLayer?.Add(this);
         }
 
         public IDropInfo DropInfo { get; set; }
@@ -25,15 +28,20 @@ public DropTargetAdorner(UIElement adornedElement, IDropInfo dropInfo)
         /// </summary>
         public Pen Pen { get; set; } = new Pen(Brushes.Gray, 2);
 
-        public void Detatch()
+        public void Detach()
         {
-            if (!m_AdornerLayer.Dispatcher.CheckAccess())
+            if (this.adornerLayer is null)
+            {
+                return;
+            }
+
+            if (!this.adornerLayer.Dispatcher.CheckAccess())
             {
-                m_AdornerLayer.Dispatcher.Invoke(this.Detatch);
+                this.adornerLayer.Dispatcher.Invoke(this.Detach);
                 return;
             }
 
-            this.m_AdornerLayer.Remove(this);
+            this.adornerLayer.Remove(this);
         }
 
         internal static DropTargetAdorner Create(Type type, UIElement adornedElement, IDropInfo dropInfo)
@@ -42,9 +50,11 @@ internal static DropTargetAdorner Create(Type type, UIElement adornedElement, ID
             {
                 throw new InvalidOperationException("The requested adorner class does not derive from DropTargetAdorner.");
             }
+
             return type.GetConstructor(new[] { typeof(UIElement), typeof(DropInfo) })?.Invoke(new object[] { adornedElement, dropInfo }) as DropTargetAdorner;
         }
 
-        private readonly AdornerLayer m_AdornerLayer;
+        [CanBeNull]
+        private readonly AdornerLayer adornerLayer;
     }
 }