iOS 响应链探索-UIResponder

首先要先了解响应者对象UIResponder，只有继承UIResponder的的类，才能处理事件。

NS_CLASS_AVAILABLE_IOS(2_0) @interface UIApplication : UIResponder

NS_CLASS_AVAILABLE_IOS(2_0) @interface UIView : UIResponder 

NS_CLASS_AVAILABLE_IOS(2_0) @interface UIViewController : UIResponder

我们可以看出UIApplication，UIView，UIViewController都是继承自UIResponder类，可以响应和处理事件。

我们下边就来探索一下响应链
首先我们分别在自定义的UIWindow，UIView，UIViewController的View
中复写下边几个方法，添加打印，看一下打印顺序

// 判断一个点是否落在范围内
- (BOOL)pointInside:(CGPoint)point withEvent:(nullable UIEvent *)event{
    BOOL isInside = [super pointInside:point withEvent:event];
    SGTLog(@" -------- pointInside  point %@ isInside %d Event %@",NSStringFromCGPoint(point),isInside,event);
    return isInside;
}
// 此方法返回的View是本次点击事件需要的最佳View
- (nullable UIView *)hitTest:(CGPoint)point withEvent:(nullable UIEvent *)event{
    SGTLog(@" -------- hitTest  point %@  Event %@",NSStringFromCGPoint(point),event);
    return [super hitTest:point withEvent:event];
}
//开始触摸
- (void)touchesBegan:(NSSet *)touches withEvent:(nullable UIEvent *)event{
    SGTLog(@"-----  touchesBegan  touches %@  event %@",touches,event);
}
//滑动
- (void)touchesMoved:(NSSet *)touches withEvent:(nullable UIEvent *)event{
    SGTLog(@" ----  touchesMoved   touches %@  event %@",touches,event);
}
//触摸结束
- (void)touchesEnded:(NSSet *)touches withEvent:(nullable UIEvent *)event{
    SGTLog(@"  ----  touchesEnded    touches %@  event %@",touches,event);
}
//触摸取消
- (void)touchesCancelled:(NSSet *)touches withEvent:(nullable UIEvent *)event{
    SGTLog(@" ----  touchesCancelled    touches %@  event %@",touches,event);
}
- (void)touchesEstimatedPropertiesUpdated:(NSSet *)touches{
    SGTLog(@" ----  touchesEstimatedPropertiesUpdated   touches %@ ",touches);
}

点击屏幕输出日志如下：

2019-04-27 10:32:29.795751+0800 ResponderDemo[67074:1346842] 
-[SGTWindow hitTest:withEvent:] [SGTWindow.m  Line:34]
 -------- fitView >
2019-04-27 10:32:29.796317+0800 ResponderDemo[67074:1346842] 
-[SGTWindow hitTest:withEvent:] [SGTWindow.m  Line:21]
 -------- hitTest  point {173, 176.66667175292969}  Event  timestamp: 201623 touches: {(
)}
2019-04-27 10:32:29.809877+0800 ResponderDemo[67074:1346842] 
-[SGTWindow pointInside:withEvent:] [SGTWindow.m  Line:16]
 -------- pointInside  point {173, 176.66667175292969} isInside 1 Event  timestamp: 201623 touches: {(
)}
2019-04-27 10:32:29.810082+0800 ResponderDemo[67074:1346842] 
-[SGTBaseView hitTest:withEvent:] [SGTBaseView.m  Line:22]
 -------- hitTest  point {173, 176.66667175292969}  Event  timestamp: 201623 touches: {(
)}
2019-04-27 10:32:29.810289+0800 ResponderDemo[67074:1346842] 
-[SGTBaseView pointInside:withEvent:] [SGTBaseView.m  Line:17]
 -------- pointInside  point {173, 176.66667175292969} isInside 1 Event  timestamp: 201623 touches: {(
)}
2019-04-27 10:32:29.810448+0800 ResponderDemo[67074:1346842] 
-[OrangeView hitTest:withEvent:] [OrangeView.m  Line:24]
 -------- hitTest  point {-97, 26.666671752929688}  Event  timestamp: 201623 touches: {(
)}
2019-04-27 10:32:29.810640+0800 ResponderDemo[67074:1346842] 
-[OrangeView pointInside:withEvent:] [OrangeView.m  Line:19]
 -------- pointInside  point {-97, 26.666671752929688} isInside 0 Event  timestamp: 201623 touches: {(
)}
2019-04-27 10:32:29.810813+0800 ResponderDemo[67074:1346842] 
-[RedView hitTest:withEvent:] [RedView.m  Line:25]
 -------- hitTest  point {73, 76.666671752929688}  Event  timestamp: 201623 touches: {(
)}
2019-04-27 10:32:29.811021+0800 ResponderDemo[67074:1346842] 
-[RedView pointInside:withEvent:] [RedView.m  Line:20]
 -------- pointInside  point {73, 76.666671752929688} isInside 1 Event  timestamp: 201623 touches: {(
)}
2019-04-27 10:32:29.811395+0800 ResponderDemo[67074:1346842] 
-[SGTBaseView hitTest:withEvent:] [SGTBaseView.m  Line:35]
 -------- fitView >
2019-04-27 10:32:29.811686+0800 ResponderDemo[67074:1346842] 
-[SGTWindow hitTest:withEvent:] [SGTWindow.m  Line:34]
 -------- fitView >
2019-04-27 10:32:29.814371+0800 ResponderDemo[67074:1346842] 
-[RedView touchesBegan:withEvent:] [RedView.m  Line:48]
 -----  touchesBegan  touches {(
     phase: Began tap count: 1 force: 0.000 window: ; layer = > view: > location in window: {173, 176.66665649414062} previous location in window: {173, 176.66665649414062} location in view: {73, 76.666656494140625} previous location in view: {73, 76.666656494140625}
)}  event  timestamp: 201623 touches: {(
     phase: Began tap count: 1 force: 0.000 window: ; layer = > view: > location in window: {173, 176.66665649414062} previous location in window: {173, 176.66665649414062} location in view: {73, 76.666656494140625} previous location in view: {73, 76.666656494140625}
)}
2019-04-27 10:32:29.920262+0800 ResponderDemo[67074:1346842] 
-[RedView touchesEnded:withEvent:] [RedView.m  Line:56]
  ----  touchesEnded    touches {(
     phase: Ended tap count: 1 force: 0.000 window: ; layer = > view: > location in window: {173, 176.66665649414062} previous location in window: {173, 176.66665649414062} location in view: {73, 76.666656494140625} previous location in view: {73, 76.666656494140625}
)}  event  timestamp: 201623 touches: {(
     phase: Ended tap count: 1 force: 0.000 window: ; layer = > view: > location in window: {173, 176.66665649414062} previous location in window: {173, 176.66665649414062} location in view: {73, 76.666656494140625} previous location in view: {73, 76.666656494140625}
)}

我们看到主要应用到下边两个方法

// 此方法返回的View是本次点击事件需要的最佳View
- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event;

// 判断一个点是否落在范围内
- (BOOL)pointInside:(CGPoint)point withEvent:(UIEvent *)event;

这个两个方法的作用是寻找到最合适的View去响应事件，我们先了解下事件的分发和传递，更便于我们了解流程：

1.当iOS程序中发生触摸事件后，系统会将事件加入到UIApplication管理的一个任务队列中
2.UIApplication将处于任务队列最前端的事件向下分发。即UIWindow。
3.UIWindow将事件向下分发，即UIView。
4.UIView首先看自己是否能处理事件，触摸点是否在自己身上。如果能，那么继续寻找子视图。
5.遍历子控件，重复以上两步。
6.如果没有找到，那么自己就是事件处理者。如果
7.如果自己不能处理，那么不做任何处理。
其中 UIView不接受事件处理的情况主要有以下三种
1）alpha <0.01
2)userInteractionEnabled = NO
3.hidden ＝ YES.

结合我们的日志输出，我们可以看到，首先调起的是Widow的hitTest:withEvent:方法，满足(alpha >=0.01
&& userInteractionEnabled == YES && hidden == NO.) 调用pointInside:withEvent:方法判断是否在当前响应区域，如果在当前区域，从后往前轮询自己的子视图，调用子视图的hitTest:withEvent:方法，一直找到最合适的响应View，返回，代码如下：

// 此方法返回的View是本次点击事件需要的最佳View
- (nullable UIView *)hitTest:(CGPoint)point withEvent:(nullable UIEvent *)event{
    SGTLog(@" -------- hitTest  point %@  Event %@",NSStringFromCGPoint(point),event);
    // 1.判断当前控件能否接收事件
    if (self.userInteractionEnabled == NO || self.hidden == YES || self.alpha <= 0.01) return nil;
    // 2. 判断点在不在当前控件
    if ([self pointInside:point withEvent:event] == NO) return nil;
    // 3.从后往前遍历自己的子控件
    NSInteger count = self.subviews.count;
    for (NSInteger i = count - 1; i >= 0; i--) {
        UIView *childView = self.subviews[i];
        // 把当前控件上的坐标系转换成子控件上的坐标系
        CGPoint childP = [self convertPoint:point toView:childView];
        UIView *fitView = [childView hitTest:childP withEvent:event];
        if (fitView) { // 寻找到最合适的view
            SGTLog(@" -------- fitView %@",fitView);
            return fitView;
        }
    }
    // 循环结束,表示没有比自己更合适的view
    return self;
//    return [super hitTest:point withEvent:event];
}

响应者链及nextResponder

响应者链

响应链是从最合适的view开始传递，处理事件传递给下一个响应者，响应者链的传递方法是事件传递的反方法，如果所有响应者都不处理事件，则事件被丢弃。我们通常用响应者链来获取上几级响应者，方法是UIResponder的nextResponder方法。
我们从上边日志中找到最合适的View是RedView，所以RedView是响应者，最终实现的是RedView的touchesBegan:withEvent:及touchesEnded:withEvent:方法，我们可以在RedView的touchesBegan或者其他方法中处理逻辑，另外如果我们想把事件传递到RedView的父视图，可以使用nextResponder来获取，使用[self.nextResponder touchesBegan:touches withEvent:event];方法可以把响应传递到下一个响应者（一般为父视图）

//开始触摸
- (void)touchesBegan:(NSSet *)touches withEvent:(nullable UIEvent *)event{
    SGTLog(@" -----  touchesBegan  touches %@  event %@",touches,event);
    [super touchesBegan:touches withEvent:event];
    [self.nextResponder touchesBegan:touches withEvent:event];
}

nextResponder

我们有时候可能会通过nextResponder来查找控件的父视图控件。

// 通过遍历view上的响应链来查找SuperView
    UIResponder *responder = self.nextResponder;
    while (responder) {
        if ([responder isKindOfClass:[SGTBaseView class]]) {
            SGTBaseView *superView = (SGTBaseView *)responder;
            SGTLog(@" -------- superView %@ ",superView);
            break;
        }
        responder = responder.nextResponder;
    }

demo地址

iOS 响应链探索-UIResponder

响应者链及nextResponder

响应者链

nextResponder

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