ios - UIGestureRecognizerState.Cancelled 与 UIGestureRecognizerState.Failed

Question

.Cancelled 和 .Failed 状态有什么区别？

将手势识别器的状态设置为.Cancelled 或.Failed 对手势识别器本身有何影响？

手势识别器的状态何时变为.Cancelled 和.Failed？

手势识别器在什么时候被标记为“已识别”？在过渡到 .Began 之后？

当是时，手势的状态是否也可以在 touchesMoved 中设置为 .Began？

例如，UIPinchGestureRecognizer 在哪个阶段识别捏合手势？我猜只在 touchesMoved 中，因为捏合是一种连续手势。

Answer 1

实际上.Cancelled 和.Failed 状态之间没有区别。两者都导致手势识别器无法处理手势。我想这只是一个命名约定。

不过，区别还在于两种状态如何影响手势处理。

这取决于手势识别器之前的状态。

1. 如果手势识别器从 .Possible 转换而来至 .Began在 touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent) (UITouchPhase.Began触摸阶段)，比用同样的方法.Failed或 .Cancelled ，队列中的下一个手势识别器(附加到 View )将有机会处理该手势。不会发送任何操作消息。
2. 但是如果手势识别器从 .Possible 转换为 .Began in touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent) (UITouchPhase.Began触摸阶段)，比在touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent) .Failed 的方法或 .Cancelled手势识别只会失败，什么也不会发生。但无论如何都会发送操作消息。
3. 如果注释掉第 8 行的代码，则手势识别将失败，下一个附加到 View 的手势识别器将有机会处理该手势。

所以这里是 View Controller :

class ViewController: UIViewController {

    func panHandler(sender: UIPanGestureRecognizer) {
         print("panHandler")
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        let customRecognizer = CustomGestureRecognizer(target: self, action: #selector(ViewController.customHandler(_:)))
        view.addGestureRecognizer(customRecognizer)

        let panRecognizer = UIPanGestureRecognizer(target: self, action: #selector(ViewController.panHandler(_:)))
        view.addGestureRecognizer(panRecognizer)

    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    func customHandler(c: CustomGestureRecognizer) {
        print("customHandler")
    }
}

这里是自定义手势识别器:

import UIKit
import UIKit.UIGestureRecognizerSubclass

class CustomGestureRecognizer: UIGestureRecognizer {

    override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent) {
        super.touchesBegan(touches, withEvent: event)
        state = .Began
        if touches.count == 1 {
            //state = .Failed
        }
        print("CustomGestureRecognizer.touchesBegan")
    }

    override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent) {
        super.touchesMoved(touches, withEvent: event)

        if state == .Failed {
            return
        }

        if touches.count == 1 {
            state = .Failed //.Cancelled
        }

        state = .Changed
        print("CustomGestureRecognizer.touchesMoved")
    }

    override func touchesEnded(touches: Set<UITouch>, withEvent event: UIEvent) {
        super.touchesEnded(touches, withEvent: event)
        state = .Ended
        print("CustomGestureRecognizer.touchesEnded")
    }
}

只需注释/取消注释第 8、10 和 23 行的代码即可查看差异。