Listfragment重叠

Question

我想创建一个音乐列表，但是当我调用listfragment时会发生与previus布局的重叠

layout

list

这是我的代码MainActivity.java

public class MainActivity extends AppCompatActivity {
Fragment_list fl;
FragmentManager fm;
FragmentTransaction ft;
Button btn;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);


}

public void click(View v)
{
    btn=(Button)findViewById(R.id.button);
    btn.setText("OK");
    fl=new Fragment_list();
    fm=getSupportFragmentManager();
    ft=fm.beginTransaction();
    ft.addToBackStack(null);
    ft.replace(R.id.Contenedor,fl);
    ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
    ft.commit();

}

}

这是listfragment代码：

public class Fragment_list extends ListFragment {

MediaPlayer player;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceStatus)
{
    File scan= Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MUSIC);
    File [] list=scan.listFiles();
    ArrayAdapter<File>adapter=new ArrayAdapter<File>(getContext(),android.R.layout.simple_list_item_1,list);
    setListAdapter(adapter);
    return super.onCreateView(inflater,container,savedInstanceStatus);
}

@Override
public void onListItemClick(ListView l,View v,int position,long id)
{
    Toast.makeText(getActivity(),"Posicion"+getListAdapter().getItem(position),Toast.LENGTH_SHORT).show();
    player= MediaPlayer.create(getActivity(), Uri.parse(String.valueOf(getListAdapter().getItem(position))));
    player.setLooping(true);
    player.start();
}

}

我只想要一个可以使用addToBack的Listfragment，如果我使用FragmentTransition发生重叠但addToBack有效，如果我使用xml片段没有重叠但我不知道如何使用addToBack