The GestureDetector does not work (example from android developer)

Question

I am reading the gesture in android at android developer, and following the tutorial I tried to run the following codes:

public class MainActivity extends Activity implements OnGestureListener, OnDoubleTapListener {

    private static final String DEBUG_TAG = "Gestures";
    private GestureDetectorCompat mDetector;

    // Called when the activity is first created.
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        View v = new RelativeLayout(this);
        v.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT));
        setContentView(v);
        mDetector = new GestureDetectorCompat(this, this);
        mDetector.setOnDoubleTapListener(this);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        this.mDetector.onTouchEvent(event);
        return super.onTouchEvent(event);
    }

    @Override
    public boolean onDown(MotionEvent event) {
        Log.d(DEBUG_TAG, "onDown: " + event.toString());
        return true;
    }

    @Override
    public boolean onFling(MotionEvent event1, MotionEvent event2, float velocityX, float velocityY) {
        Log.d(DEBUG_TAG, "onFling: " + event1.toString() + event2.toString());
        return true;
    }

    @Override
    public void onLongPress(MotionEvent event) {
        Log.d(DEBUG_TAG, "onLongPress: " + event.toString());
    }

    @Override
    public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
        Log.d(DEBUG_TAG, "onScroll: " + e1.toString() + e2.toString());
        return true;
    }

    @Override
    public void onShowPress(MotionEvent event) {
        Log.d(DEBUG_TAG, "onShowPress: " + event.toString());
    }

    @Override
    public boolean onSingleTapUp(MotionEvent event) {
        Log.d(DEBUG_TAG, "onSingleTapUp: " + event.toString());
        return true;
    }

    @Override
    public boolean onDoubleTap(MotionEvent event) {
        Log.d(DEBUG_TAG, "onDoubleTap: " + event.toString());
        return true;
    }

    @Override
    public boolean onDoubleTapEvent(MotionEvent event) {
        Log.d(DEBUG_TAG, "onDoubleTapEvent: " + event.toString());
        return true;
    }

    @Override
    public boolean onSingleTapConfirmed(MotionEvent event) {
        Log.d(DEBUG_TAG, "onSingleTapConfirmed: " + event.toString());
        return true;
    }
}

The codes came from the site here.

But when I ran the app, I got no debug information when I click or long press the view.

BTW, I test the app in both emulator and htc e1 device.

What is the problem?

Answer 1

You are creating a GestureDetector but you are never "hooking it up" to your View. Try changing your onCreate like this:

super.onCreate(savedInstanceState);
View v = new RelativeLayout(this);
v.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT));
setContentView(v);
mDetector = new GestureDetectorCompat(this, this);
mDetector.setOnDoubleTapListener(this);
v.setOnTouchListener(new OnTouchListener(){
    public boolean onTouch(View v, MotionEvent me){
        return mDetector.onTouchEvent(me);
    }
});

Answer 2

Little late, but my solution of this problem is:

@Override
public boolean onTouchEvent(MotionEvent event) {
    this.mDetector.onTouchEvent(event);
    return super.onTouchEvent(event);
}

The return of the Detector gone lost. Change to:

@Override
public boolean onTouchEvent(MotionEvent event) {
    if (this.mDetector != null) return this.mDetector.onTouchEvent(event);
   return super.onTouchEvent(event);
}

But is this a good solution? Time for Android Insider. ;)

Tschau Fred