Add hook in drag handler to handle exceptions occurred when data is d…

…ropped.

Examples/DefaultsExample/Data.cs

@@ -49,6 +49,12 @@ public virtual void Dropped(IDropInfo dropInfo)
     public virtual void DragCancelled()
     {
     }
+
+
+    public bool ExceptionOccurred(Exception ex)
+    {
+        return false;
+    }
   }
 
   internal class Data : IDropTarget

GongSolutions.Wpf.DragDrop/DefaultDragHandler.cs

@@ -33,5 +33,11 @@ public virtual void Dropped(IDropInfo dropInfo)
     public virtual void DragCancelled()
     {
     }
+
+
+    public virtual bool ExceptionOccurred(System.Exception ex)
+    {
+        return false;
+    }
   }
 }

GongSolutions.Wpf.DragDrop/DragDrop.cs

@@ -797,6 +797,11 @@ private static void DragSource_PreviewMouseMove(object sender, MouseEventArgs e)
                 if (result == DragDropEffects.None)
                   dragHandler.DragCancelled();
               }
+              catch (Exception ex)
+              {
+                  if (!dragHandler.ExceptionOccurred(ex))
+                      throw;
+              }
               finally {
                 m_DragInProgress = false;
               }

GongSolutions.Wpf.DragDrop/IDragSource.cs

@@ -44,5 +44,17 @@ public interface IDragSource
     /// Notifies the drag handler that a drag has been aborted.
     /// </summary>
     void DragCancelled();
+
+    /// <summary>
+    /// Notifies that an exception has occurred upon dragging.
+    /// </summary>
+    /// <param name="ex">
+    ///     The exception that occurrred.
+    /// </param>
+    /// <returns>
+    /// Boolean indicating whether the exception is handled in the drag handler.
+    /// False will rethrow the exception.
+    /// </returns>
+    bool ExceptionOccurred(Exception ex);
   }
 }