How to restrict a draggable UIView to specific bounds - ios

Question

I have a UIImageView which I have made Draggable via a custom class called DraggableImageView2. The class is then instantiated in a UIViewController with an image and can be dragged within a UIView. The thing is I want to restrict the UIImageView not to go past the specific boundaries when dragged. Here is my current code:
import UIKit
class DraggableImageView2: UIImageView, UIGestureRecognizerDelegate {
var dragStartPositionRelativeToCenter : CGPoint?
var dragGesture: UIGestureRecognizer!
var zoomGesture: UIGestureRecognizer!
var lastKnownCenterX: CGFloat = 0.0
var lastKnownCenterY: CGFloat = 0.0
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
self.initializeGestures()
}
override init(image: UIImage?) {
super.init(image: image)
self.initializeGestures()
}
override init(frame: CGRect) {
super.init(frame: frame)
self.initializeGestures()
}
func initializeGestures() {
self.userInteractionEnabled = true
self.multipleTouchEnabled = true
dragGesture = UIPanGestureRecognizer(target: self, action: #selector(DraggableImageView.handlePan(_:)))
self.addGestureRecognizer(dragGesture)
}
func handlePan(recognizer: UIPanGestureRecognizer!) {
Scripts.log("PAN >>> MOVE ACTIVATED")
if recognizer.state == UIGestureRecognizerState.Began {
let locationInView = recognizer.locationInView(superview)
dragStartPositionRelativeToCenter = CGPoint(x: locationInView.x - center.x, y: locationInView.y - center.y)
return
}
if recognizer.state == UIGestureRecognizerState.Ended {
dragStartPositionRelativeToCenter = nil
return
}
let locationInView = recognizer.locationInView(superview)
Scripts.log("PAN LOCATION >>> X = \(self.frame.origin.x) | Y = \(self.frame.origin.y) | LX = \(locationInView.x) | LY = \(locationInView.y) | DX = \(self.dragStartPositionRelativeToCenter!.x) | DY = \(self.dragStartPositionRelativeToCenter!.y)")
let xDragMin: CGFloat = 1.0
let yDragMin: CGFloat = 1.0
let xDragMax: CGFloat = kDEVICE_WIDTH - self.frame.size.width - 1.0
let yDragMax: CGFloat = kDEVICE_WIDTH - self.frame.size.height - 1.0
var newCenterX: CGFloat = locationInView.x - self.dragStartPositionRelativeToCenter!.x
var newCenterY: CGFloat = locationInView.y - self.dragStartPositionRelativeToCenter!.y
if self.frame.origin.x < xDragMin {
Scripts.log("PAN LOCATION >>> X MIN PAST BOUNDS")
newCenterX = lastKnownCenterX
}
if self.frame.origin.y < yDragMin {
Scripts.log("PAN LOCATION >>> Y MIN PAST BOUNDS")
newCenterY = lastKnownCenterY
}
if self.frame.origin.x > xDragMax {
Scripts.log("PAN LOCATION >>> X MAX PAST BOUNDS")
}
if self.frame.origin.y > yDragMax {
Scripts.log("PAN LOCATION >>> Y MAX PAST BOUNDS")
}
UIView.animateWithDuration(0.1) {
self.center = CGPoint(x: newCenterX,
y: newCenterY)
}
lastKnownCenterX = newCenterX
lastKnownCenterY = newCenterY
}
func handlePinch(recognizer: UIPinchGestureRecognizer!) {
Scripts.log("PINCH >>> ZOOM ACTIVATED")
//self.bringSubviewToFront(recognizer.view!)
recognizer.view?.transform = CGAffineTransformScale((recognizer.view?.transform)!, recognizer.scale, recognizer.scale)
recognizer.scale = 1
}
func gestureRecognizer(gestureRecognizer: UIGestureRecognizer, shouldRecognizeSimultaneouslyWithGestureRecognizer otherGestureRecognizer: UIGestureRecognizer) -> Bool {
Scripts.log("shouldRecognizeSimultaneouslyWithGestureRecognizer WAS CALLED")
return true
}
}
I've only started working on the xDragMin and yDragMin portion. Everything works for stopping it when it is less than the xDragMin, but the problem becomes for some strange reason, when you try to drag out of it, it gets frozen in that X Point. Same for the yDragMin, one if reaches the min, it stops as it should, but can't drag out of the Y Point.

Answer 1

So after some more digging and playing around, I seem to have been able to solve my own problem, at least for the X Bounds Min. Here is what I did:
(1) Added these new variables
var isWithinXBounds: Bool = true
var lastKnownLX: CGFloat = 0.0
(2) The logic starting with "if self.frame.origin.x < xDragMin" needed to be fine tuned. This condition is perfectly fine until it hits the X bounds. Once it does then self.frame.origin.x will never change (DUH) cos now its position is locked. I need another condition to check that once the bounds has been hit i.e. locked, check if the users touch is moving in a +ve direction. If so, then set the BOOL value back to TRUE which will unlock the x position
if self.frame.origin.x < xDragMin {
Scripts.log("PAN LOCATION >>> X MIN PAST BOUNDS")
self.isWithinXBounds = false
//If TOUCH still moving in negative direction
if locationInView.x - lastKnownLX < 0 {
newCenterX = lastKnownCenterX
}
else {
self.isWithinXBounds = true
}
}
(3) Here is the condition that will then unlock the UIImageView based on the BOOL value:
if isWithinXBounds {
lastKnownCenterX = newCenterX
lastKnownLX = locationInView.x
}