I found existing tutorials on how to do this to be a bit complicated. Here's how to do simple fling detection in four directions: public interface FlingListener {   void onTopToBottom();   void onBottomToTop();   void onLeftToRight();   void onRightToLeft(); }  public class FlingDetector {   static final int SWIPE_MIN_DISTANCE = 120;   static final int SWIPE_MAX_OFF_PATH = 250;   static final int SWIPE_THRESHOLD_VELOCITY = 200;      private final GestureDetector gestureDetector;    public FlingDetector(final FlingListener listener) {     gestureDetector = new GestureDetector(new GestureDetector.SimpleOnGestureListener() {       @Override       public boolean onFling(MotionEvent e1, MotionEvent e2,           float velocityX, float velocityY) {         if (Math.abs(e1.getY() - e2.getY()) > SWIPE_MAX_OFF_PATH) {           if (Math.abs(e1.getX() - e2.getX()) > SWIPE_MAX_OFF_PATH               || Math.abs(velocityY)  SWIPE_MIN_DISTANCE) {             listener.onBottomToTop();     ...
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