无法在Android中设置自定义界面侦听器

Question

我正在尝试从活动到自定义视图设置接口侦听器，但它正在抛出NullPointerException。当我触摸CustomRelativeLayout时，它将通过dispatchTouchEvent回调方法处理，但它会抛出异常 请帮帮我...

CustomRelativeLayout.class

public class CustomRelativeLayout extends RelativeLayout {

private static final String TAG = "CustomRelative";


private MapsActivity.MapTouchable mapTouchable;

public CustomRelativeLayout(Context context) {
    super(context);
}

public CustomRelativeLayout(Context context, AttributeSet attrs) {
    super(context, attrs);
}

public CustomRelativeLayout(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
}

@Override
public boolean dispatchTouchEvent(MotionEvent event) {


    switch (event.getAction()) {

        case MotionEvent.ACTION_DOWN:
            Log.e(TAG, "dispatchTouchEvent: Action Down");
            mapTouchable.onMapTouchEvent(true);
            break;

        case MotionEvent.ACTION_UP:
            Log.e(TAG, "dispatchTouchEvent: Action Up");
            mapTouchable.onMapTouchEvent(false);

            break;
        case MotionEvent.ACTION_MOVE:
            Log.e(TAG, "dispatchTouchEvent: Action Move");
            mapTouchable.onMapTouchEvent(true);

            break;
    }
    return super.dispatchTouchEvent(event);
}



public void setOnMapTouchListner(MapsActivity.MapTouchable mapsActivity) {
    mapTouchable =  mapsActivity;
}
}

这里是活动类

public class MapsActivity extends FragmentActivity {

private static final String TAG = "MapsActivity";


private CustomRelativeLayout rl_screenview;


public interface MapTouchable {
    void onMapTouchEvent(boolean isTouch);
}

MapTouchable mapTouchable = new MapTouchable() {
    @Override
    public void onMapTouchEvent(boolean isTouch) {
        Log.e(TAG, "onMapTouchEvent() called with: " + "isTouch = [" + isTouch + "]");
    }
};


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_maps);
    Log.e(TAG, "onCreate: ");

    rl_screenview = (CustomRelativeLayout)findViewById(R.id.rl_screenview);
    // here i am setting listner to customrelativelayout
    rl_screenview.setOnMapTouchListner(mapTouchable);

}
}

帮助将被宣布......