在android中，如何在拖放后将按钮保持在上一个位置

在我的android应用程序中，我有一个gridlayout，其中有五个linearlayout。四个linearlayout分别包含一个按钮，另一个linearlayout为空。我想将一个按钮拖放到空的linearlayout，当linearlayout不为空时，在拖放后，它将采用其先前的linearlayout位置。使用此代码

 ViewGroup owner = (ViewGroup) view.getParent();    
 LinearLayout pastContainer = (LinearLayout) owner;

LinearLayout newcontainer = (LinearLayout) v;
int count = newcontainer.getChildCount();

如果目标linearlayout不为空（have child），则获取要保留按钮的linearlayout。我让TargetLinearLayout的子级使用此代码检查它是否为空

 ViewGroup owner = (ViewGroup) view.getParent();    
 LinearLayout pastContainer = (LinearLayout) owner;

LinearLayout newcontainer = (LinearLayout) v;
int count = newcontainer.getChildCount();

我可以将按钮拖放到空的linearlayout，但当我尝试将按钮拖放到带有子对象的linearlayout时，会出现错误。这是我的密码

private class MyDragListener implements OnDragListener 
{
    @Override
    public boolean onDrag(View v, DragEvent event) 
    {
        int action = event.getAction();
          switch (event.getAction()) {
          case DragEvent.ACTION_DRAG_STARTED:
            // Do nothing
            break;
          case DragEvent.ACTION_DRAG_ENTERED:
            break;
          case DragEvent.ACTION_DRAG_EXITED:
            break;
          case DragEvent.ACTION_DROP:

            View view = (View) event.getLocalState();
            ViewGroup owner = (ViewGroup) view.getParent(); 
            LinearLayout pastContainer = (LinearLayout) owner;
            LinearLayout newcontainer = (LinearLayout) v;
            int count = newcontainer.getChildCount();                           

            if(count==0)
            {
                owner.removeView(view);     
                newcontainer.addView(view);
                view.setVisibility(View.VISIBLE);
            }
            else
            {
                pastContainer.addView(view);
                view.setVisibility(View.VISIBLE);
            }

            break;
          case DragEvent.ACTION_DRAG_ENDED:
          default:
            break;
          }
          return true;
    }             
}

如果目标linearlayout不为空（有子项），如何将按钮保持为上一个linearlayout？谢谢