ios - 如何将可拖动的 UIView 限制在特定范围内

Question

我有一个 UIImageView，我通过名为 DraggableImageView2 的自定义类将其设置为 Draggable。然后该类在带有图像的 UIViewController 中实例化，并且可以在 UIView 中拖动。问题是我想限制 UIImageView 在拖动时不要超过特定边界。这是我当前的代码:

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

    }

}

我才开始处理 xDragMin 和 yDragMin 部分。当它小于 xDragMin 时，一切都可以停止它，但是由于一些奇怪的原因，问题变成了，当你试图拖出它时，它被卡住在那里X 点。 yDragMin也是一样，如果到达最小值，它应该停止，但不能拖出 Y 点。

Answer 1

所以经过更多的挖掘和尝试，我似乎已经能够解决我自己的问题，至少对于 X Bounds Min。这是我所做的:

(1) 添加了这些新变量

var isWithinXBounds: Bool = true
var lastKnownLX: CGFloat = 0.0

(2) 需要微调以“if self.frame.origin.x < xDragMin”开头的逻辑。在达到 X 边界之前，这种情况非常好。一旦完成，self.frame.origin.x 将永远不会改变 (DUH) 因为现在它的位置被锁定了。我需要另一个条件来检查一旦边界被击中即锁定，检查用户触摸是否在 +ve 方向移动。如果是，则将 BOOL 值设置回 TRUE，这将解锁 x 位置

  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) 下面是根据 BOOL 值解锁 UIImageView 的条件:

if isWithinXBounds {

        lastKnownCenterX = newCenterX
        lastKnownLX = locationInView.x

    }