Detecting the direction of PAN gesture in iOS

Question

In my app there is a image view.Im adding PAN gesture to that image view.

This is working fine.

The image view is in landscape mode.

I want to increase a count in label while user pan to right direction and decrease that count while user pan to left direction.

I googled a lot but didn't find a solution for this.

Can anyone please help me how to detect the direction in which the user is panning(left/right)?

Answer 1

In the target selector of your gesture recognizer, use - (CGPoint)velocityInView:(UIView *)view; :

- (void)panRecognized:(UIPanGestureRecognizer *)rec
{
    CGPoint vel = [rec velocityInView:self.view];
    if (vel.x > 0)
    {
        // user dragged towards the right
        counter++;
    }
    else
    {
        // user dragged towards the left
        counter--;
    }
}

Ps: I didn't know about this method until approx. 3 minutes before. One of Google's first hits was the official Apple documentation.

Answer 2

Something like this:

- (void)pan:(UIPanGestureRecognizer *)sender
{

    typedef NS_ENUM(NSUInteger, UIPanGestureRecognizerDirection) {
        UIPanGestureRecognizerDirectionUndefined,
        UIPanGestureRecognizerDirectionUp,
        UIPanGestureRecognizerDirectionDown,
        UIPanGestureRecognizerDirectionLeft,
        UIPanGestureRecognizerDirectionRight
    };

    static UIPanGestureRecognizerDirection direction = UIPanGestureRecognizerDirectionUndefined;

    switch (sender.state) {

        case UIGestureRecognizerStateBegan: {

            if (direction == UIPanGestureRecognizerDirectionUndefined) {

                CGPoint velocity = [sender velocityInView:recognizer.view];

                BOOL isVerticalGesture = fabs(velocity.y) > fabs(velocity.x);

                if (isVerticalGesture) {
                    if (velocity.y > 0) {
                        direction = UIPanGestureRecognizerDirectionDown;
                    } else {
                        direction = UIPanGestureRecognizerDirectionUp;
                    }
                }

                else {
                    if (velocity.x > 0) {
                        direction = UIPanGestureRecognizerDirectionRight;
                    } else {
                        direction = UIPanGestureRecognizerDirectionLeft;
                    }
                }
            }

            break;
        }

        case UIGestureRecognizerStateChanged: {
            switch (direction) {
                case UIPanGestureRecognizerDirectionUp: {
                    [self handleUpwardsGesture:sender];
                    break;
                }
                case UIPanGestureRecognizerDirectionDown: {
                    [self handleDownwardsGesture:sender];
                    break;
                }
                case UIPanGestureRecognizerDirectionLeft: {
                    [self handleLeftGesture:sender];
                    break;
                }
                case UIPanGestureRecognizerDirectionRight: {
                    [self handleRightGesture:sender];
                    break;
                }
                default: {
                    break;
                }
            }
        }

        case UIGestureRecognizerStateEnded: {
            direction = UIPanGestureRecognizerDirectionUndefined;   
            break;
        }

        default:
            break;
    }

}

- (void)handleUpwardsGesture:(UIPanGestureRecognizer *)sender
{
    NSLog(@"Up");
}

- (void)handleDownwardsGesture:(UIPanGestureRecognizer *)sender
{
    NSLog(@"Down");
}

- (void)handleLeftGesture:(UIPanGestureRecognizer *)sender
{
    NSLog(@"Left");
}

- (void)handleRightGesture:(UIPanGestureRecognizer *)sender
{
    NSLog(@"Right");
}

Answer 3

My previous answer in Swift

public enum Direction: Int {
    case Up
    case Down
    case Left
    case Right

    public var isX: Bool { return self == .Left || self == .Right }
    public var isY: Bool { return !isX }
}

public extension UIPanGestureRecognizer {

    public var direction: Direction? {
        let velocity = velocityInView(view)
        let vertical = fabs(velocity.y) > fabs(velocity.x)
        switch (vertical, velocity.x, velocity.y) {
        case (true, _, let y) where y < 0: return .Up
        case (true, _, let y) where y > 0: return .Down
        case (false, let x, _) where x > 0: return .Right
        case (false, let x, _) where x < 0: return .Left
        default: return nil
        }
    }
}

Answer 4

Here is a cleaned up Swift 5 version, with example of usage:

public enum PanDirection: Int {
    case up, down, left, right
    public var isVertical: Bool { return [.up, .down].contains(self) }
    public var isHorizontal: Bool { return !isVertical }
}

public extension UIPanGestureRecognizer {

   var direction: PanDirection? {
        let velocity = self.velocity(in: view)
        let isVertical = abs(velocity.y) > abs(velocity.x)
        switch (isVertical, velocity.x, velocity.y) {
        case (true, _, let y) where y < 0: return .up
        case (true, _, let y) where y > 0: return .down
        case (false, let x, _) where x > 0: return .right
        case (false, let x, _) where x < 0: return .left
        default: return nil
        }
    }

}

@IBAction func pan(_ recognizer: UIPanGestureRecognizer) {        
    if let direction = recognizer.direction {
        if direction.isVertical {
            //do what you want when pan is vertical
        } else if direction == .left {
            //do what you want when pan is left
        }
    }
}

Answer 5

Rewrite Adam Waite version on Swift 3

public enum PanDirection: Int {
    case up,
    down,
    left,
    right

    public var isX: Bool {
        return self == .left || self == .right
    }

    public var isY: Bool {
        return !isX
    }
}

extension UIPanGestureRecognizer {
    var direction: PanDirection? {
        let velocity = self.velocity(in: view)
        let vertical = fabs(velocity.y) > fabs(velocity.x)
        switch (vertical, velocity.x, velocity.y) {
        case (true, _, let y):
            return y < 0 ? .up : .down

        case (false, let x, _):
            return x > 0 ? .right : .left
        }
    }
}

Answer 6

Note that Adam's Swift version above has a mistake. .up should return if y < 0 and .down should return if y > 0 (they're reversed).

So:

//MARK: - Direction
internal enum Direction {
    case up
    case down
    case left
    case right
}

//MARK: - UIPanGestureRecognizer
internal extension UIPanGestureRecognizer {
    internal var direction: Direction? {
        let velocity = velocityInView(view)
        let isVertical = fabs(velocity.y) > fabs(velocity.x)

        switch (isVertical, velocity.x, velocity.y) {
            case (true, _, let y) where y < 0: return .up
            case (true, _, let y) where y > 0: return .down
            case (false, let x, _) where x > 0: return .right
            case (false, let x, _) where x < 0: return .left
            default: return nil
        }
    }
}

Answer 7

judging by velocity is too sensitive to me, user easily mixed tapping screen with panning a small part.

So I use custom UIPanGestureRecognizer . Swift 5

enum Orientation{
    case lhs, rhs, `default`
}



class HPan: UIPanGestureRecognizer {

    var first: CGPoint?
    var orient = .default

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent) {
        super.touchesBegan(touches, with: event)

        state = .began
        first = touches.first?.location(in: view?.window)
    }


    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent) {
        super.touchesMoved(touches, with: event)
        if state == .cancelled{
            return
        }
        if let location = touches.first?.location(in: view?.window), let begin = first{
          let magicDistance: CGFloat = 20
          if location.x - begin.x > magicDistance{
               orient = .rhs
               state = .ended
          }  
          else if begin.x - location.x > magicDistance{
               orient = .lhs
               state = .ended
          }  
        }

    }



    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent) {
        super.touchesEnded(touches, with: event)
        state = .ended
    }



    override func touchesCancelled(_ touches: Set<UITouch>, with event: UIEvent) {
        super.touchesCancelled(touches, with: event)
        state = .cancelled
    }


    override func reset() {
        super.reset()

        state = .possible
        isRight = false
        orient = .default
    }
}

Call like this:

@objc func push(_ gesture: RightPan){
        if gesture.state == UIGestureRecognizer.State.ended{
            switch gesture.orient{
                case .lhs:
                     counter -= 1
                case .rhs:
                     counter += 1
                default:
                    ()        
            }
        }

    }