Question

我正在实现自定义UIGestureRecognizer子类。

我希望以velocityInView:完成UIPanGestureRecognizer的方式实施{{1}}。但我不知道如何去做。如何以pts / sec计算速度？

Answer 1

首先，如果您使用的是Swift，则需要创建一个桥接标题和#import <UIKit/UIGestureRecognizerSubclass.h>，以便您可以覆盖UIGestureRegoniser的触摸开始/移动/取消/结束方法。如果您正在使用Objective-C，请将该import语句放在.h或.m文件中。

其次，一旦你创建了UIGestureRecogniser子类，你需要这些变量：

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，继续设置一切你需要覆盖以下方法，我认为这些都是相当自我解释的：

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一点 - 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
}

使用以下等式计算速度：

velocity = deltaDistance / deltaTime

在这种情况下，取速度（x和y）的每个分量，并使用该等式计算每个轴的速度。如果你想要结合速度的两个组成部分，你可以像这样使用毕达哥拉斯定理：

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，并使用action在屏幕上拖动时获取速度：

override func viewDidLoad() {
    super.viewDidLoad()

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

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

如何实现velocityInView：自定义手势识别器？

1 个答案: