How to detect swipe direction between left/right and up/down

Question

My Question: How do I detect when a user moves their finger up/down vs left/right (and how do I know which direction of those groups their finger moved)?

My Situation: I want to change the brightness of my app when they move their finger up and down (up = brighter, down = darker), and I want to switch between activities and/or views based on their left/right swipe.

Answer 1

I wrote a simple class for this: it's well documented so I wont explain it here

public class OnSwipeListener extends GestureDetector.SimpleOnGestureListener {      @Override     public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {          // Grab two events located on the plane at e1=(x1, y1) and e2=(x2, y2)         // Let e1 be the initial event         // e2 can be located at 4 different positions, consider the following diagram         // (Assume that lines are separated by 90 degrees.)         //         //         //         \ A  /         //          \  /         //       D   e1   B         //          /  \         //         / C  \         //         // So if (x2,y2) falls in region:         //  A => it's an UP swipe         //  B => it's a RIGHT swipe         //  C => it's a DOWN swipe         //  D => it's a LEFT swipe         //          float x1 = e1.getX();         float y1 = e1.getY();          float x2 = e2.getX();         float y2 = e2.getY();          Direction direction = getDirection(x1,y1,x2,y2);         return onSwipe(direction);     }      /** Override this method. The Direction enum will tell you how the user swiped. */     public boolean onSwipe(Direction direction){         return false;     }      /**      * Given two points in the plane p1=(x1, x2) and p2=(y1, y1), this method      * returns the direction that an arrow pointing from p1 to p2 would have.      * @param x1 the x position of the first point      * @param y1 the y position of the first point      * @param x2 the x position of the second point      * @param y2 the y position of the second point      * @return the direction      */     public Direction getDirection(float x1, float y1, float x2, float y2){         double angle = getAngle(x1, y1, x2, y2);         return Direction.fromAngle(angle);     }      /**      *      * Finds the angle between two points in the plane (x1,y1) and (x2, y2)      * The angle is measured with 0/360 being the X-axis to the right, angles      * increase counter clockwise.      *      * @param x1 the x position of the first point      * @param y1 the y position of the first point      * @param x2 the x position of the second point      * @param y2 the y position of the second point      * @return the angle between two points      */     public double getAngle(float x1, float y1, float x2, float y2) {          double rad = Math.atan2(y1-y2,x2-x1) + Math.PI;         return (rad*180/Math.PI + 180)%360;     }       public enum Direction{         up,         down,         left,         right;          /**          * Returns a direction given an angle.          * Directions are defined as follows:          *          * Up: [45, 135]          * Right: [0,45] and [315, 360]          * Down: [225, 315]          * Left: [135, 225]          *          * @param angle an angle from 0 to 360 - e          * @return the direction of an angle          */         public static Direction fromAngle(double angle){             if(inRange(angle, 45, 135)){                 return Direction.up;             }             else if(inRange(angle, 0,45) || inRange(angle, 315, 360)){                 return Direction.right;             }             else if(inRange(angle, 225, 315)){                 return Direction.down;             }             else{                return Direction.left;            }          }         /**          * @param angle an angle          * @param init the initial bound          * @param end the final bound          * @return returns true if the given angle is in the interval [init, end).          */         private static boolean inRange(double angle, float init, float end){             return (angle >= init) && (angle < end);         }     }  } 

To use simply extend the OnSwipeListener and override the onSwipe method

Answer 2

You simply have to extend SimpleOnGestureListener class,

Declare this in your class,

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; 

As an example for horizontal swipe you can see the below code,

 class MyGestureDetector 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;             }             // right to left swipe             if (e1.getX() - e2.getX() > SWIPE_MIN_DISTANCE                     && Math.abs(velocityX) > SWIPE_THRESHOLD_VELOCITY) {                 onLeftSwipe();             }              // left to right swipe             else if (e2.getX() - e1.getX() > SWIPE_MIN_DISTANCE                     && Math.abs(velocityX) > SWIPE_THRESHOLD_VELOCITY) {                 onRightSwipe();             }         } catch (Exception e) {          }         return false;       }    } 

You can do this similarly for vertical swipe purpose.