关于代码添加Fragmnet问题

*/
private void addContentFragment(){
//Fragmnet管理器
android.app.FragmentManager fragmentManager = getFragmentManager();
//开启一个事物
android.app.FragmentTransaction ft = fragmentManager.beginTransaction();
contentFragment = new ContentFragment();
ft.add(R.id.ff,contentFragment);
//提交事物
ft.commit();
}
以上代码添加Fragmnet 时错误提示:
java.lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first.
如何解决呢

http://jingyan.baidu.com/article/3ea51489c40bdc52e71bba69.html