Add Gesture Recognizer to element off-screen

Question

I have a view that is twice as wide as my device screen and have swiping gesture recognizers that move the view either left or right. But I have come to realize that the view will not perform the gesture action if the swipe is performed on a portion of the view that was initially off-screen.

// View twice as wide as the device screen
let masterView = UILabel(frame: CGRect(x: 0, y: 0, width: self.view.frame.width * 2, height: 100))

let swipeLeftGesture = UISwipeGestureRecognizer(target: self, action: #selector(ThisViewController.swipeLeft))
let swipeRightGesture = UISwipeGestureRecognizer(target: self, action: #selector(ThisViewController.swipeRight))
swipeLeftGesture.direction = UISwipeGestureRecognizerDirection.left
swipeRightGesture.direction = UISwipeGestureRecognizerDirection.right
masterView.addGestureRecognizer(swipeLeftGesture)
masterView.addGestureRecognizer(swipeRightGesture)
self.addSubview(masterView)


func swipeLeft() {        
    // Moves masterView to the left equal to that of the width of the screen (or half of masterView's total width)
    let moveLeftFrame = CGRect(x: (masterView.frame.width / 2) * -1, y: masterView.frame.minY, width: masterView.frame.width, height: masterView.frame.height)

    UIView.animateKeyframes(withDuration: 0.5, delay: 0, options: .calculationModeCubic, animations: {
        UIView.addKeyframe(withRelativeStartTime: 0.0, relativeDuration: 0.4, animations: {
            masterView.frame = moveLeftFrame
        })
    }, completion: { (true) in

    })
}


func swipeRight() {        
    // Moves masterView back to original location
    let moveRightFrame = CGRect(x: 0, y: masterView.frame.minY, width: masterView.frame.width, height: masterView.frame.height)

    UIView.animateKeyframes(withDuration: 0.5, delay: 0, options: .calculationModeCubic, animations: {
        UIView.addKeyframe(withRelativeStartTime: 0.0, relativeDuration: 0.4, animations: {
            masterView.frame = moveRightFrame
        })
    }, completion: { (true) in

    })
}

So after swiping to the left to see the other half of the view (which is loaded off-screen), I am unable to swipe back to the right. Can gestures not be performed on a location that was loaded off-screen?

EDIT: So after tinkering a bit, I see that the gesture is not recognized on any location of the view that is loaded off-screen. So if I move the view to see, say, 50 pixels that started off off-screen, gestures aren't being recognized on that 50 pixels.

Answer 1

I don't really understand your answer but hopefully this helps

So what I think your problem is

1. the way you're declaring your swiping function is wrong. Instead of func swipeLeft() change it to func swipeLeft(sender: UISwipeGestureRecognizer)

or

2. the problem could be the way you're declaring your frame variables. you can view the changed one in my code.

.code.

func swipeLeft(sender: UISwipeGestureRecognizer) {        
    // Moves masterView to the left equal to that of the width of the screen (or half of masterView's total width)
    let moveLeftFrame = CGRect(x: -view.frame.width, y: 0, width: masterView.frame.width, height: masterView.frame.height)

    UIView.animateKeyframes(withDuration: 0.5, delay: 0, options: .calculationModeCubic, animations: {
        UIView.addKeyframe(withRelativeStartTime: 0.0, relativeDuration: 0.4, animations: {
            masterView.frame = moveLeftFrame
        })
    }, completion: { (true) in

    })
}

func swipeRight(sender: UISwipeGestureRecognizer) {        
    // Moves masterView back to original location
    let moveRightFrame = CGRect(x: 0, y: 0, width: masterView.frame.width, height: masterView.frame.height)

    UIView.animateKeyframes(withDuration: 0.5, delay: 0, options: .calculationModeCubic, animations: {
        UIView.addKeyframe(withRelativeStartTime: 0.0, relativeDuration: 0.4, animations: {
            masterView.frame = moveRightFrame
        })
    }, completion: { (true) in

    })
}