android - Control which directions the ViewPager can be scrolled, dynamically with UI feedback

Question

I'm working on an app which uses many pages to swipe through, however at some pages I would like to be able to prevent scrolling to the next page until they've selected something.

At the moment I've extended ViewPager:

/* (non-Javadoc)
 * @see android.support.v4.view.ViewPager#onInterceptTouchEvent(android.view.MotionEvent)
 */
@Override
public boolean onInterceptTouchEvent(MotionEvent event) {
    if (this.canGoLeft || this.canGoRight) {
        return super.onInterceptTouchEvent(event);
    }

    return false;
}

/* (non-Javadoc)
 * @see android.support.v4.view.ViewPager#onTouchEvent(android.view.MotionEvent)
 */
@Override
public boolean onTouchEvent(MotionEvent ev) {
    boolean lockScroll = false;
    switch (ev.getAction()) {
    case MotionEvent.ACTION_DOWN:
        lastX = ev.getX();
        lockScroll = false;
        return super.onTouchEvent(ev);
    case MotionEvent.ACTION_MOVE:
        if (canGoLeft && lastX < ev.getX()) {
            lockScroll = false;
        } else if (canGoRight && lastX > ev.getX()) {
            lockScroll = false;
        } else {
            lockScroll = true;
        }


        lastX = ev.getX();

        break;
    }

    lastX = ev.getX();

    if (lockScroll) {
        //make callback to prevent movement
        if (mOnPreventCallback != null) {
            mOnPreventCallback.onPreventMovement();
        }
        return false;
    } else {
        return super.onTouchEvent(ev);
    }
}

Note: I've tried to implement prevent swiping to previous however you can still swipe to the previous page but you need to swipe from the uttermost left side and swipe right a bit. It's temperamental but it does not prevent swiping completely.

Three things I want to do here:

1. Prevent scrolling to next screen until they have selected an item or something
2. Prevent scrolling to previous screen throughout (partially implemented)
3. Give feedback to the user to show that scrolling is disabled, like the way Android shows the top and bottom screens with a gradient.

Answer 1

When I faced a similar problem, I made my own Listener with a gestureDetector and made it not respond to swiping at all, you can easily adjust it to not respond to swiping to the right only under some condition. This should answer your numbers 1 and 2.

This is the listener:

public class OnSwipeTouchListener implements OnTouchListener {

@SuppressWarnings("deprecation")
private final GestureDetector gestureDetector = new GestureDetector(new GestureListener());

public boolean onTouch(final View v, final MotionEvent event) {
    return gestureDetector.onTouchEvent(event);
}

private final class GestureListener extends SimpleOnGestureListener {

    private static final int SWIPE_THRESHOLD = 100;
    private static final int SWIPE_VELOCITY_THRESHOLD = 100;

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


    @Override
    public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
        boolean result = false;
        try {
            float diffY = e2.getY() - e1.getY();
            float diffX = e2.getX() - e1.getX();
            if (Math.abs(diffX) > Math.abs(diffY)) {
                if (Math.abs(diffX) > SWIPE_THRESHOLD && Math.abs(velocityX) > SWIPE_VELOCITY_THRESHOLD) {
                    if (diffX > 0) {
                        onSwipeRight();
                    } else {
                        onSwipeLeft();
                    }
                }
            } else {
               // onTouch(e);
            }
        } catch (Exception exception) {
            exception.printStackTrace();
        }
        return result;
    }
}
public void onTouch(MotionEvent e) {
}
public void onSwipeRight() {
//call this only if your condition was set
}

public void onSwipeLeft() {
//nothing, this means,swipes to left will be ignored
}

public void onSwipeTop() {
}

public void onSwipeBottom() {
}
}

and this is an example of use :

viewPager.setOnTouchListener(new OnSwipeTouchListener() {
public void onSwipeRight() {
  if(your conditionIsMet){
// move your pager view to the right
     }
   }

});

There might be a simpler and more elegant solution, but this worked well for me.