private void ttddMain_TabDrop(object sender, TabDropEventArgs args)
 {
     if (DropLocation.Center == args.Location || 0 == ttcMain.Items.Count)
     {
         ttcMain.DropTab(args.TearableTab);
     }
     else
     {
         AddSplitControl(args.Location, DropLocation.NA, args.TearableTab);
     }
 }
 public abstract void OnTabDrop(object sender, TabDropEventArgs args);