首先，如果您使用Swift，则需要创建一个桥接头和#import <UIKit/UIGestureRecognizerSubclass.h>，以便可以覆盖UIGestureRegoniser的开始/移动/取消/结束方法。如果使用的是Objective，只需将import语句放在.h或.m文件中即可。

其次，一旦创建了UIGestureRecognizer子类，就需要在其中包含以下变量：

private lazy var displayLink: CADisplayLink = {
    let link = CADisplayLink(target: self, selector: Selector("timerCalled"))
    link.addToRunLoop(NSRunLoop.currentRunLoop(), forMode: NSRunLoopCommonModes)
    return link
}()

private var previousTouchLocation: CGPoint?
private var currentTouchLocation : CGPoint?

private var previousTime: Double?
private var currentTime : Double?

显示链接用于更新currentTime和previousTime。

第三，继续设置您需要覆盖以下方法所需的一切，我认为这都是不言自明的：

override func touchesBegan(touches: Set<NSObject>!, withEvent event: UIEvent!) {
    self.state = .Began
    displayLink.paused = false
}

override func touchesMoved(touches: Set<NSObject>!, withEvent event: UIEvent!) {
    if let view = self.view,
        touch = touches.first as? UITouch {
        self.state = .Changed

        let newLocation = touch.locationInView(view)
        self.previousTouchLocation = self.currentTouchLocation
        self.currentTouchLocation = newLocation
    }
}

override func touchesEnded(touches: Set<NSObject>!, withEvent event: UIEvent!) {
    self.state = .Ended
    displayLink.paused = true
}

override func touchesCancelled(touches: Set<NSObject>!, withEvent event: UIEvent!) {
    self.state = .Cancelled
    displayLink.paused = true
}

第四，，现在我们可以得到更有趣的位--计算速度：

func velocityInView(targetView: UIView) -> CGPoint {
    var velocity = CGPoint.zeroPoint

    if let view = self.view,
        prevTouchLocation = self.previousTouchLocation,
        currTouchLocation = self.currentTouchLocation,
        previousTime = self.previousTime,
        currentTime  = self.currentTime {

        let targetPrevLocation = view.convertPoint(prevTouchLocation, toView: targetView)
        let targetCurrLocation = view.convertPoint(currTouchLocation, toView: targetView)

        let deltaTime = CGFloat(currentTime - previousTime)

        let velocityX = (targetCurrLocation.x - targetPrevLocation.x) / deltaTime
        let velocityY = (targetCurrLocation.y - targetPrevLocation.y) / deltaTime

        velocity = CGPoint(x: velocityX, y: velocityY)
    }

    return velocity
}

速度是用以下公式计算的：

velocity = deltaDistance / deltaTime

在这种情况下，取速度的每个分量(x和y)，并使用这个方程来计算每个轴上的速度。如果你想把速度的两个成分结合起来，你可以使用毕达哥拉斯定理，如下所示：

let distance = hypot(targetCurrLocation.x - targetPrevLocation.x, 
                     targetCurrLocation.y - targetPrevLocation.y)
let velocity = distance / deltaTime

第五，在视图控制器中，您现在可以添加手势识别器，并在拖动屏幕时使用action获取速度：

override func viewDidLoad() {
    super.viewDidLoad()

    let recognizer = VelocityGestureRecognizer(target: self, action: Selector("movedGesture:"))
    self.view.addGestureRecognizer(recognizer)
}

func movedGesture(recognizer: VelocityGestureRecognizer) {
    let v = recognizer.velocityInView(self.view)
    println("velocity = \(v)")
}

票数 2

页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持

原文链接：

https://stackoverflow.com/questions/28552408

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问如何为自定义手势识别器实现velocityInView：？
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