如何为自定义手势识别器实现 velocityInView:？

Question

我正在实现自定义 UIGestureRecognizer 子类。

我想按照 UIPanGestureRecognizer 的方式实施 velocityInView:。但我不确定该怎么做。如何计算以点/秒为单位的速度？

Answer 1

首先， 如果您使用 Swift，您将需要创建一个桥接头和 #import <UIKit/UIGestureRecognizerSubclass.h>，这样您就可以覆盖 UIGestureRegoniser 涉及 began/moved/cancelled/ended 方法。如果您使用 Objective-C，只需将 import 语句放在 .h 或 .m 文件中即可。

其次，一旦您创建了 UIGestureRecognizer 子类，您需要在其中添加这些变量：

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link用于更新currentTime和previousTime。

第三，要继续设置您需要重写以下方法的所有内容，我认为这一切都是不言自明的：

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，现在我们可以进入更有趣的部分 - 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
}

使用以下公式计算速度：

velocity = deltaDistance / deltaTime

在这种情况下，取速度的每个分量（x 和 y）并使用该方程式计算每个轴上的速度。如果你想结合速度的两个分量，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， 在您的视图控制器中，您现在可以添加手势识别器并使用 action 获取在屏幕上拖动时的速度：

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)")
}

如何为自定义手势识别器实现 velocityInView:？

How do I implement velocityInView: for a custom gesture recognizer?

subclass

objective-c

uigesturerecognizer

ios