事件的传递和响应

响应链

image.png

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    self.window.rootViewController = [[ViewController alloc] init];
    [self.window makeKeyAndVisible];
    return YES;
}
 
- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    UIView *view = [[UIView alloc] init];
    [self.view addSubview:view];
    
    UILabel *label = [[UILabel alloc] init];
    [view addSubview:label];
    [self logOutResponderChain:label];
}

- (void)logOutResponderChain:(UIResponder *)responder {
    UIResponder *nextResponder = responder.nextResponder;
    NSLog(@"%@ -> ", NSStringFromClass([responder class]));
    while (nextResponder) {
        NSLog(@"%@ -> ", NSStringFromClass([nextResponder class]));
        nextResponder = nextResponder.nextResponder;
    }
    NSLog(@"*");
}
// - 打印结果 : UILabel -> UIView -> UIView -> ViewController -> UIDropShadowView -> UITransitionView -> UIWindow -> UIWindowScene -> UIApplication -> AppDelegate -> *

1. 能响应事件的 必须是UIResponser的子类;
2. 响应链是 子视图-> 父视图的.

传递链

image.png

1. 首先判断主窗口（keyWindow）自己是否能接受触摸事件
2. 判断触摸点是否在自己身上
3. 子控件数组中从后往前遍历子控件，重复前面的两个步骤（所谓从后往前遍历子控件，就是首先查找子控件数组中最后一个元素(后添加到view上的子view - > 先添加到view上的子view)，然后执行1、2步骤）
4. view，比如叫做fitView，那么会把这个事件交给这个fitView，再遍历这个fitView的子控件，直至没有更合适的view为止。
5. 如果没有符合条件的子控件，那么就认为自己最合适处理这个事件，也就是自己是最合适的view。

- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event {
    NSLog(@"AView --- hitTest");
    UIView * view = [super hitTest:point withEvent:event];
    NSLog(@"AView --- hitTest --- return %@", view.class);
    return view;
}

- (BOOL)pointInside:(CGPoint)point withEvent:(UIEvent *)event {
    NSLog(@"AView --- pointInside");
    return [super pointInside:point withEvent:event];
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    NSLog(@"AView --- touchesBegan");
}
// - [vc.view addSubView: AView]; [AView addSubView: BView]; [BView addSubView: CView];

// - 触摸CView
AView --- hitTest
AView --- pointInside --- Yes
BView --- hitTest
BView --- pointInside --- Yes
CView --- hitTest
CView --- pointInside --- Yes
CView --- hitTest --- return CView
BView --- hitTest --- return CView
AView --- hitTest --- return CView
CView --- touchesBegan

// - 触摸BView但是不触摸CView
AView --- hitTest
AView --- pointInside --- Yes
BView --- hitTest
BView --- pointInside --- Yes
CView --- hitTest
CView --- pointInside --- No
CView --- hitTest --- return (null)
BView --- hitTest --- return BView
AView --- hitTest --- return BView
BView --- touchesBegan

总结

用户产生触摸事件 -> 事件进入UIApplication事件队列 -> UIApplication分发事件给keyWindow -> [UIWindow hitTest:withEvent:] -> [UIView hitTest:withEvent:] -> … -> [UIView hitTest:withEvent:] -> 返回最合适的view给keyWindow -> [UIWindow _sendTouchesForEvent:] -> [UIView touchesBegan:withEvent:]。