ios - UIGestureRecognizerState.Cancelled与UIGestureRecognizerState.Failed

.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如何影响手势识别器本身？

手势识别器的状态何时变为.Cancelled和.Failed？

手势识别器在哪一点标记为“已识别”？过渡到.Began后？

是的话，手势的状态也可以设置为.Began中的touchesMoved吗？

例如，在哪个阶段UIPinchGestureRecognizer可以识别捏捏手势？我猜只是在touchesMoved中，因为捏是一种连续手势。

最佳答案

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

但是，不同之处还在于两种状态如何影响手势处理。

这取决于手势识别器的先前状态。

如果手势识别器从.Possible(触摸的.Began阶段)中的touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent)转换为UITouchPhase.Began，而不是使用相同的方法转换为.Failed或.Cancelled，则队列中的下一个手势识别器(附加到视图)将有机会处理手势。没有动作消息将被发送。

但是，如果手势识别器在touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent)(触摸的UITouchPhase.Began阶段)中从.Possible转换为.Begin，则从touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent)方法转换为.Failed或.Cancelled时，手势识别将完全失败，并且将不会发生任何事情。但是无论如何都会发送动作消息。

如果在第8行注释掉了代码，则手势识别将失败，并且附加到视图的下一个手势识别器将有机会处理该手势。

因此，这里的视图控制器:

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")
    }
}

这里是一个自定义手势识别器:

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行上的代码，即可看到不同之处。

关于ios - UIGestureRecognizerState.Cancelled与UIGestureRecognizerState.Failed，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/38574921/