Android - Trouble with swipe gesture

Question

I'm trying to implement a swipe gesture in my app. I've made almost all code but it doesn't work.

Here is the code I have in my Activity:

// Swipe detector
gestureDetector = new GestureDetector(new SwipeGesture(this));
gestureListener = new OnTouchListener() {
    public boolean onTouch(View v, MotionEvent event)
    {
        Log.e("", "It works");
        return gestureDetector.onTouchEvent(event);
    }
};

LinearLayout root = (LinearLayout) findViewById(R.id.rules_root);
root.setOnTouchListener(gestureListener);

When I touch the screen, the logcat displays it works.

Here he my the code of the class SwipeGesture:

public class SwipeGesture extends SimpleOnGestureListener
{
    private static final int SWIPE_MIN_DISTANCE = 120;
    private static final int SWIPE_MAX_OFF_PATH = 250;
    private static final int SWIPE_THRESHOLD_VELOCITY = 200;

    private Activity activity;

    public SwipeGesture(Activity activity)
    {
        super();
        this.activity = activity;
    }

    @Override
    public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY)
    {
        Log.e("", "Here I am");
        try
        {
            if (Math.abs(e1.getY() - e2.getY()) > SWIPE_MAX_OFF_PATH) return false;
            if(e1.getX() - e2.getX() > SWIPE_MIN_DISTANCE && Math.abs(velocityX) > SWIPE_THRESHOLD_VELOCITY)
            {
                if ( ((TabActivity) activity.getParent()).getTabHost() != null )
                {
                    TabHost th = ((TabActivity) activity.getParent()).getTabHost();
                    th.setCurrentTab(th.getCurrentTab() - 1);
                }
                else
                {
                    activity.finish();
                }
                Log.e("", "Swipe left");
            }
            else if (e2.getX() - e1.getX() > SWIPE_MIN_DISTANCE && Math.abs(velocityX) > SWIPE_THRESHOLD_VELOCITY)
            {
                if ( ((TabActivity) activity.getParent()).getTabHost() != null )
                {
                    TabHost th = ((TabActivity) activity.getParent()).getTabHost();
                    th.setCurrentTab(th.getCurrentTab() + 1);
                }
                Log.e("", "Swipe right");
            }
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
        return false;
    }
}

The line Log.e("", "Here I am"); is never displayed. So I presume the onFling method is never called.

Any ideas of why this doesn't work?

Thanks.

Regards.

V.

Answer 1

In your SimpleOnGestureListener, override onDown for your gestures to register. It can just return true but it has to be defined like this..

@Override
    public boolean onDown(MotionEvent e) {
            return true;
    }

....See this link.. and the comment below the answer..

Answer 2

You need to change a couple of things, here's an example.

Set your OnTouchListener:

root.setOnTouchListener(new View.OnTouchListener() {
            public boolean onTouch(View v, MotionEvent event) {
                if (gestureDetector.onTouchEvent(event)) {
                    return false;
                }
                return false;
            }
        });

SwipeGesture class:

class SwipeGesture extends SimpleOnGestureListener {
    @Override
    public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX,
            float velocityY) {

        try {
            if (Math.abs(e1.getY() - e2.getY()) > SWIPE_MAX_OFF_PATH)
                return false;
            if (e1.getX() - e2.getX() > SWIPE_MIN_DISTANCE
                    && Math.abs(velocityX) > SWIPE_THRESHOLD_VELOCITY) {
//Do something

                return true;
            } else if (e2.getX() - e1.getX() > SWIPE_MIN_DISTANCE
                    && Math.abs(velocityX) > SWIPE_THRESHOLD_VELOCITY) {
//Do something
                return true;

            }

        } catch (Exception e) {
            Log.e("Fling", "There was an error processing the Fling event:"
                    + e.getMessage());
        }
        return true;
    }

    // Necessary for the onFling event to register
    @Override
    public boolean onDown(MotionEvent e) {
        return true;
    }
}

It looks like you're swiping between Tabs. Using Fragments and ViewPager is much easier and smoother for your users.