C#

ClassA (objects are stored in SortedListA)
 |   |
 |   |----> reference to object of ClassB (objects are stored in SortedListB)
 |
 |--------> reference to object of ClassC (objects are stored in SortedListC)

private void button_DragOver(object sender, DragEventArgs e)
{
  // You can use any DragDropEffects that you want.
  if (e.Data.GetDataPresent("MyCustomFormat") &&
      (e.AllowedEffect & DragDropEffects.Link) != 0)
    e.Effect = DragDropEffects.Link;
}
private void button_DragDrop(object sender, DragEventArgs e)
{
  if ((e.AllowedEffect & DragDropEffects.Link) != 0)
  {
    object o = e.Data.GetData("MyCustomFormat");
    if (o != null)
    {
      // Store the object for the Click event handler.
      this.currentListItem = o;
 
      // Just call the Click event handler.
      this.button_Click(sender, EventArgs.Empty);
    }
  }
}