iOS事件处理和响应链

说到iOS中的触摸事件不得不提到两个内容：一个是UIResponder、一个是事件的响应链

什么UIResponser？

Responsder objects是UIResponder的实例化对象，他组成了事件处理的骨架，许多关键对象都是UIResponder对象包括UIApplication、UIViewController、UIView也包括UIWindow。
也就是说只要继承UIResponder的类都可以相应事件。

一般我们通过重写UIResponder的四个方法来处理事件

// 一根或者多根手指开始触摸view
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
// 一根或者多根手指在view上移动，【会多次调用】
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
// 一根或者多根手指离开view
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
// 触摸结束前，某个系统事件(例如电话呼入)会打断触摸过程
- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event
// 提示：touches中存放的都是UITouch对象

响应链

一个触摸事件是从用户点击屏幕开始 由UIApplication向下分发 经由 UIWindow 在向下传递给UIViewController和UIVIew
那么 我们一个UIViewController有那么多View到底事件应该交给谁消费掉呢？
有两个重要的方法

• hitTest:withEvent:
• pointInside:withEvent:

他们的作用分别是
hitTest:withEvent:寻找并返回最合适的view、
pointInside:withEvent: 判断点是否在当前的View上

• 两个方法调用顺序
  我们通过实例验证一下 新建四个View并重写他们的touchesXXX方法、hitTest:withEvent: 方法、以及pointInside:withEvent:方法并打印方法名和类名

  
  
  views

//示例 其他View以此为模板
#import "GrayView.h"

@implementation GrayView

- (void)layoutSubviews
{
    self.backgroundColor = [UIColor grayColor];
}

- (BOOL)pointInside:(CGPoint)point withEvent:(UIEvent *)event
{
    NSLog(@"%@ pointInside", NSStringFromClass([self class]));
    return [super pointInside:point withEvent:event];
}

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

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    
    NSLog(@"%@ touchBegan", NSStringFromClass([self class]));
    [super touchesBegan:touches withEvent:event];
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    NSLog(@"%@ touchesMoved",NSStringFromClass([self class]));
    [super touchesMoved:touches withEvent:event];
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    NSLog(@"%@ touchesEnded", NSStringFromClass([self class]));
    [super touchesEnded:touches withEvent:event];
}

- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event
{
    NSLog(@"%@ touchesCancelled", NSStringFromClass([self class]));
    [super touchesCancelled:touches withEvent:event];
}

@end

//在ViewController中添加他们
//ViewController.m
GrayView *grayView = [[GrayView alloc] initWithFrame:CGRectMake(50.f, 100.f, 260.f, 200.f)];
    
    RedView *redView = [[RedView alloc] initWithFrame:CGRectMake(0.f, 0.f, 120.f, 100.f)];
    
    BlueView *blueView = [[BlueView alloc] initWithFrame:CGRectMake(140.f, 100.f, 100.f, 100.f)];
    
    YellowView *yellowView = [[YellowView alloc] initWithFrame:CGRectMake(50.f, 360.f, 200.f, 200.f)];
    
    [self.view addSubview:grayView];
    [grayView addSubview:redView];
    [grayView addSubview:blueView];
    [self.view addSubview:yellowView];

运行后的效果图

运行图

当我们点击灰色View时，控制台打印如下信息

console

我们看到最先调用了YellowView的hitTest方法而后调用pointInside方法，如果pointInside返回NO说明这个触摸点不在这个View上就遍历跟他同一级的下一个View，如果pointInside返回YES说明触摸点在这个View的范围内，则逆序遍历他的子View，如果子View的pointInside都返回NO那么说明这个触摸点在当前返回YES的这个View上

有几点回影响hitTest流程当

• alpha<=0.01
• userInterActionEnabled = NO
• hidden = YES;
  pointInside都会返回NO

我们可以根据上面的结论自己写一下hitTest的内部逻辑验证推论是否正确

//GrayView.m
- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event
{
   
    NSLog(@"%s",__func__);
    //逆序遍历子VIew看触摸点是否在子View中
    NSArray *subViews = [[self.subviews reverseObjectEnumerator] allObjects];
    UIView *tmpView = nil;
    for (UIView *view in subViews) {
        
        CGPoint convertedPoint = [self convertPoint:point toView:view];
        if ([view pointInside:convertedPoint withEvent:event]) {
            
            tmpView = view;
            break;
            
        }
        
    }
    
  
    
    if (tmpView) {
    //在子View中
        return tmpView;
    } else if([self pointInside:point withEvent:event]) {
        //点不在子View中而在自己身上
        return self;
    } else {
        //触摸点不在当前View上
        return nil;
        
    }
    

}

我们依然点击GrayView发现依然可以找到正确被点击的View

console

现在我们给RedView的hitTest方法打一个断点看并点击RedView查看调用层级

responder_chain