问OnTouchScreen在安卓系统中不起作用

EN

public class GameActivity extends Activity
    implements OnTouchListener  {
    @Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    //Intent intent = getIntent();
    setContentView(R.layout.layout_game);

    //create grid view
    splitImage(); 
    GridView gridView = new GridView(this);
    gridView = (GridView)findViewById(R.id.grid_view);   
    final ImageAdapter images = new ImageAdapter(this,chunkedImages);
    final GridView gV = gridView;
     gridView.setAdapter(images);
} 
....
public boolean onTouch(View v, MotionEvent me) {

    switch(me.getAction())
    {
    case MotionEvent.ACTION_DOWN :
        Toast.makeText(GameActivity.this, "down" , Toast.LENGTH_SHORT).show();
        break;
    case MotionEvent.ACTION_UP :
        Toast.makeText(GameActivity.this, "up", Toast.LENGTH_SHORT).show();
        break;
    case MotionEvent.ACTION_MOVE :
        Toast.makeText(GameActivity.this, "move", Toast.LENGTH_SHORT).show();
        break;
    }
    return true;
}

 }