iOS - 点击事件与响应链

一、点击事件涉及到哪些？

touchBegan
uicontrol
gestureRecognizer

二、点击事件如何传递和响应？

传递链
响应链
hitTest/pointInside

三、结合以上原理处理的问题和应用

iOS中的事件可以分为3大类型：

触屏事件(例如点击按钮、通过手势缩放图片、拖动上下滚动页面等)
传感器事件(例如摇一摇红包、通过旋转设备控制赛车方向、指南针等)
远程控制事件(例如耳机的线控、外接手柄、遥控器等)

UITouch/UIEvent

点击事件都是基于触屏事件，执行以下代码看看。

override func touchesBegan(_ touches: Set, with event: UIEvent?) {
        print(touches)
        print(event)
    }

我单手指点击了1次屏幕，得到以下结果。

[ 
phase: Began 
tap count: 1 
window: ;
        layer = > 
        
view: > 
        
location in window: {128, 505} 
previous location in window: {128, 505}

location in view: {128, 505} 
previous location in view: {128, 505}]

Optional(
timestamp: 351596 
touches: {(
     
    phase: Began 
    tap count: 1 
        window: ; 
        layer = >
        
        view: >
        
        location in window: {128, 505}
        previous location in window: {128, 505} 
        location in view: {128, 505} 
        previous location in view: {128, 505}
)})

UITouch的Set中的这个UITouch包含了

phase
tap count
window
view
location in window(this/previous)
location in view(this/previous)

这边的UIEvent是自己的子类UITouchesEvent，这边UIEvent包含的属性看起来其实就是UITouch。既然是完全包含关系，为什么要有两个参数呢？

于是我两个手指同时点击屏幕了1次，得到以下结果。

[ phase: Began 
tap count: 1 
window: ;
         layer = > 

view: > 

location in window: {62.5, 444.5} 
previous location in window: {62.5, 444.5}
location in view: {62.5, 444.5} 
previous location in view: {62.5, 444.5}]

Optional( timestamp: 352692 touches: {(
     phase: Began tap count: 1 window: ; layer = > view: > location in window: {62.5, 444.5} previous location in window: {62.5, 444.5} location in view: {62.5, 444.5} previous location in view: {62.5, 444.5},
     phase: Began tap count: 1 window: ; layer = > view: (null) location in window: {256, 545.5} previous location in window: {256, 545.5} location in view: {256, 545.5} previous location in view: {256, 545.5}
)})

UITouchedEvent我就不展开了，这边看到里面是有两个UITouch，所以1个手指点击1次屏幕是一个UITouch。

那我快速点击屏幕两次。

[ phase: Began tap count: 1 window: ; layer = > view: > location in window: {182, 504} previous location in window: {182, 504} location in view: {182, 504} previous location in view: {182, 504}]
Optional( timestamp: 352928 touches: {(
     phase: Began tap count: 1 window: ; layer = > view: > location in window: {182, 504} previous location in window: {182, 504} location in view: {182, 504} previous location in view: {182, 504}
)})
[ phase: Began tap count: 2 window: ; layer = > view: > location in window: {182.5, 504.5} previous location in window: {182.5, 504.5} location in view: {182.5, 504.5} previous location in view: {182.5, 504.5}]
Optional( timestamp: 352928 touches: {(
     phase: Began tap count: 2 window: ; layer = > view: > location in window: {182.5, 504.5} previous location in window: {182.5, 504.5} location in view: {182.5, 504.5} previous location in view: {182.5, 504.5}
)})

看到这边第二次的时候，tap count是2

我慢速点击屏幕2次，结果如下：

[ phase: Began tap count: 1 window: ; layer = > view: > location in window: {182.5, 480} previous location in window: {182.5, 480} location in view: {182.5, 480} previous location in view: {182.5, 480}]
Optional( timestamp: 353057 touches: {(
     phase: Began tap count: 1 window: ; layer = > view: > location in window: {182.5, 480} previous location in window: {182.5, 480} location in view: {182.5, 480} previous location in view: {182.5, 480}
)})
[ phase: Began tap count: 1 window: ; layer = > view: > location in window: {186, 493.5} previous location in window: {186, 493.5} location in view: {186, 493.5} previous location in view: {186, 493.5}]
Optional( timestamp: 353058 touches: {(
     phase: Began tap count: 1 window: ; layer = > view: > location in window: {186, 493.5} previous location in window: {186, 493.5} location in view: {186, 493.5} previous location in view: {186, 493.5}
)})

两次Tap count都是1，所以连续点击的时候，时间间隔是一个重要标志。某一个时间段内，会作为count为2次，而过了这个时间段，都变成独立的点击了。所以联想到了tapgesture numberoftaps，应该也是基于这个机制。

这里有个小发现，iOS10及以上在UITouch里面多了Force属性，即压力传感器。当然屏幕压力force属性，在touchBegan和touchEnded是0，只有TouchMove的时候才有值，最大值是6.667，最小是0

[ phase: Moved 
tap count: 1 
force: 6.667 
window: ; layer = > view: > location in window: {221.5, 449.5} previous location in window: {221.5, 449.5} location in view: {221.5, 449.5} previous location in view: {221.5, 449.5}]

Optional( timestamp: 51618.7 touches: {(
     phase: Moved tap count: 1 force: 6.667 window: ; layer = > view: > location in window: {221.5, 449.5} previous location in window: {221.5, 449.5} location in view: {221.5, 449.5} previous location in view: {221.5, 449.5}
)})

而location的精度是0.5pt。这里关于iOS系统版本对UITouch支持，大家可以看一下UITouch在UIKit中的接口，就是Control+Command+点击进去看看。

Gesture recognizer和UIKit的一些控件如UIButton等都是基于UITouch/UIEvent和Began/Moved/Ended/Cancelled。

iOS处理触屏事件，触屏事件分为两种方式：

高级事件处理：利用UIKit提供的各种用户控件或者手势识别器来处理事件。
低级事件处理：在UIView的子类中重写触屏回调方法，直接处理触屏事件。
如果想监听一个view上面的触摸事件，之前的做法是：

（1）自定义一个view。

（2）实现view的touches方法，在方法内部实现具体处理代码。

通过touches方法监听view触摸事件，有很明显的几个缺点：

（1）必须得自定义view。

（2）由于是在view内部的touches方法中监听触摸事件，因此默认情况下，无法让其他外界对象监听view的触摸事件。

（3）不容易区分用户的具体手势行为。

UIGestureRecognizer

iOS 3.2后，苹果推出了手势识别功能（Gesture Recognizer），在触摸事件处理方面，大大简化了开发者的开发难度。

手势识别器UIGestureRecognizer类的实例也是处理触屏事件的好帮手，其内部也使用目标行为表。
包含了7种手势

UITapGestureRecognizer：点击（单击、双击、三连击等）手势
UIPinchGestureRecognizer：缩放手势
UIPanGestureRecognizer：拖拽手势
UISwipeGestureRecognizer：滑动手势
UIRotationGestureRecognizer：旋转手势
UILongPressGestureRecognizer：长按手势
UIScreenEdgePanGestureRecognizer: 屏幕边缘平移

UIControl

UIKit中我们常用的是UIControl类实例的addTarget:action:forControlEvents:方法维护控件目标行为表，除了UIKit控件外，

点击后如何找到响应者

hitTest

hitTest: withEvent:方法
事件传递的时候调用
当事件传递给控件的时候，就会调用控件的这个方法，去寻找最合适的view
作用：寻找最合适的view

pointInside

pointInside:withEvent:方法
作用：判断当前这个点在不在方法调用者（控件）上
当两个控件有重叠，需要将事件判断是哪一个控件执行的时候

响应是如何传递的

在iOS中只有继承了UIResponder的对象才能接收并处理事件称为响应者对象
UIApplication,UIViewController,UIView都继承自UIResponder,因此他们都是响应者对象, 都能够接收并处理事件。

继承自UIResponder的类能处理事件是由于UIResponder内部提供了以下方法

override func touchesBegan(_ touches: Set, with event: UIEvent?) {}
override func touchesMoved(_ touches: Set, with event: UIEvent?) {}
override func touchesEnded(_ touches: Set, with event: UIEvent?) {}
override func touchesCancelled(_ touches: Set, with event: UIEvent?) {}

通过如下方法传递给下一个响应者

override func touchesBegan(_ touches: Set, with event: UIEvent?) {
    self.next?.touchesBegan(touches, with: event)
}

手势和点击事件重叠如何响应

如何解决手势和手势重叠？

覆盖在上一层的View实现UIGestureRecognizerDelegate协议中的方法

gestureRecognizer:shouldRecognizeSimultaneouslyWithGestureRecognizer

如何解决手势和单击事件重叠?

UIGestureRecognizer 有个属性cancelsTouchesInView,这个属性默认值是true，即当手势识别成功后，会发送touchesCancelled消息给view来结束view的响应。
如果cancelsTouchesInView为false，那么gestureRecognizer和view都可以响应