title: MessageBox in file drag+drop event-handler causes Windows explorer to freeze
body: <p><strong>Scenario:</strong> C#/WPF application with dragdrop enabled for a UI-Control. When dragging a file from Windows Explorer and dropping it on the UI-Control a MessageBox appears.</p>
  
  <p><strong>Problem:</strong> As long as the MessageBox is not clicked away (by hitting "OK") Windows Explorer is frozen and (probably) waits for the drag-drop event to return.</p>
  
  <p><strong>Question:</strong> Is there any way to release Windows Explorer from its wait <em>before</em> the MessageBox is shown? What about the "<a href="https://msdn.microsoft.com/en-us/library/system.windows.drageventargs(v=vs.110).aspx" rel="nofollow noreferrer">Handled</a>" property of the "DragEventArgs" Class?</p>
  
  <p><strong>Code:</strong></p>
  
  <pre><code> private void OnDrop_ButtonOpen(object sender, DragEventArgs e)
   {
     if (e.Data.GetDataPresent(DataFormats.FileDrop))
     {
       string[] files = (string[])e.Data.GetData(DataFormats.FileDrop);
       MessageBox.Show(files[0]);
     }
   }
  </code></pre>
  
  <p>PS: Others similar questions exist. However, no solution to "prematurely" return the event.</p>