UIGestureRecognizerState.Cancelled 对比 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 'recognized'？过渡到 .Began 之后？

如果是，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 因为捏是一个连续的手势。

Answer 1

以下是

之间的区别

.Cancelled

The gesture recognizer has received touches resulting in the cancellation of a continuous gesture. It sends its action message (or messages) at the next cycle of the run loop and resets its state to UIGestureRecognizerStatePossible.

和

.Failed

The gesture recognizer has received a multi-touch sequence that it cannot recognize as its gesture. No action message is sent and the gesture recognizer is reset to UIGestureRecognizerStatePossible.

换句话说，.Cancelled在连续手势被打断时被调用。 .Failed 当手势未被识别为某种类型的手势时调用。

Answer 2

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，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。

如果手势识别器在 touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent)（触摸的 UITouchPhase.Began 阶段）从 .Possible 过渡到 .Began，则与 .Failed 或 .Cancelled，队列中的下一个手势识别器（附加到视图）将有机会处理该手势。不会发送任何操作消息。
但是如果手势识别器在 touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent)（触摸的 UITouchPhase.Began 阶段）从 .Possible 过渡到 .Began，则比在 touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent) 方法中过渡到 .Failed或 .Cancelled 手势识别将完全失败，什么也不会发生。但是无论如何都会发送操作消息。
如果注释掉第 8 行的代码，那么手势识别将失败，下一个附加到视图的手势识别器将有机会处理该手势。

所以这里是视图控制器：

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 comment/uncomment 第 8、10 和 23 行的代码即可查看差异。

UIGestureRecognizerState.Cancelled 对比 UIGestureRecognizerState.Failed

UIGestureRecognizerState.Cancelled vs UIGestureRecognizerState.Failed

objective-c

gesture-recognition

uigesturerecognizer

ios

swift