如何将可拖动的 UIView 限制在特定范围内

Posted 2023-03-13

【中文标题】如何将可拖动的 UIView 限制在特定范围内

【英文标题】：How to restrict a draggable UIView to specific bounds

【发布时间】：2016-06-02 14:29:55

【问题描述】：

我有一个 UIImageView，我通过一个名为 DraggableImageView2 的自定义类将其设为 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 在拖动时不要越过特定边界。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

    

我才开始研究xDragMin 和yDragMin 部分。当它小于 xDragMin 时，一切都可以阻止它，但是由于某种奇怪的原因，当你试图拖出它时，它会冻结在那个 X 点。 yDragMin 也一样，如果达到最小值，它会按原样停止，但不能拖出 Y 点。

【问题讨论】：

您可以尝试记录lastKnownCenterX 和lastKnownCenterY 吗？如果这些值以某种方式设置为小于 xDragMin 或 xDragY 的值，那么您的视图框架肯定会卡在该位置。

@KyleParent 刚刚尝试记录它。不，似乎最后一个已知点的设置小于 Drag Min Points。这是一个冻结的示例输出： LAST KNOWN LOCATION :PRE: >>> X = 56.75 | Y = 301.75 最后一个已知位置 :POST: >>> X = 56.75 | Y = 301.75

当lastKnownCenterX 为56.75 时，视图的frame.origin.x 是多少？

啊，所以我的怀疑是正确的 - 不知何故，您的视图被允许通过 xDragMin 阈值。一旦发生这种情况，您将始终点击第一个条件并设置newCenterX = lastKnownCenterX，其中lastKnownCenterX 已经离左边太远了。我建议重新审视用于计算 newCenterX 和 newCenterX 的逻辑。不应该是var newCenterX: CGFloat = locationInView.x + self.dragStartPositionRelativeToCenter!.x吗？

@KyleParent 这不起作用，但我认为您的线索和建议帮助我确定了我认为问题所在，尤其是在添加更多日志之后。我认为的问题是这种逻辑“如果 self.frame.origin.x

【参考方案1】：

所以经过更多的挖掘和玩耍之后，我似乎已经能够解决我自己的问题，至少对于 X Bounds Min 而言。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) 以“if self.frame.origin.x

  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