The delegates receive messages from a gesture recognizer, and their responses to these messages enable them to affect the operation of the gesture recognizer or to specify a relationship between it and another gesture recognizer, such as allowing simultaneous recognition or setting up a dynamic failure requirement.

　　这些委托从手势识别器接收消息，它们会响应这些消息以能够影响到手势识别器的操作或指定它与另外一个手势识别器的关系，例如，允许同时识别或设置动态的失败需求。

　　An example of a situation where dynamic failure requirements are useful is in an app that attaches a screen-edge pan gesture recognizer to a view. In this case, you might want all other relevant gesture recognizers associated with that view's subtree to require the screen-edge gesture recognizer to fail so you can prevent any graphical glitches that might occur when the other recognizers get canceled after starting the recognition process. To do this, you could use code similar to the following:

　　在应用程序中动态的失败需求例子，应用程序将屏幕边缘的pan手势绑定到一个视图上，在这种情况下，您可能希望与该视图的子树关联的所有其他相关手势识别器都要求屏幕边缘手势识别器失败，这样就可以防止在启动识别过程后取消其他识别器时可能出现的任何图形错误。如果想做到这一点，你可以使用类似于下面的代码：

let myScreenEdgePanGestureRecognizer = UIScreenEdgePanGestureRecognizer(target: self, action:#selector(handleScreenEdgePan))

myScreenEdgePanGestureRecognizer.delegate = self

    // Configure the gesture recognizer and attach it to the view.

...

func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldBeRequiredToFailBy otherGestureRecognizer: UIGestureRecognizer) -> Bool {

    guard let myView = myScreenEdgePanGestureRecognizer.view,

          let otherView = otherGestureRecognizer.view else { return false }

    return gestureRecognizer == myScreenEdgePanGestureRecognizer &&

           otherView.isDescendant(of: myView)}

gestureRecognizer(_:shouldRecognizeSimultaneouslyWith:)

　　Asks the delegate if two gesture recognizers should be allowed to recognize gestures simultaneously.

　　询问委托代理是否允许两个手势识别器同时识别手势。

optional func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer,

shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer) -> Bool

　Return Value

　Discussion