UI视图1、事件传递&响应UIView/CALayerUIView提供内容，负责处理触摸等事件，继承UIResponsd

1、事件传递 & 响应

UIView/CALayer

UIView提供内容，负责处理触摸等事件，继承UIResponsder
CALayer负责内容显示

事件传递

- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event;
- (BOOL)pointInside:(CGPoint)point withEvent:(UIEvent *)event;

- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event
{
    if (!self.userInteractionEnabled || [self isHidden] || self.alpha <= 0.01) {
        return nil;
    }
    
    if ([self pointInside:point withEvent:event]) {
        __block UIView *hit = nil;
        [self.subviews enumerateObjectsWithOptions:NSEnumerationReverse usingBlock:^(__kindof UIView * _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
            CGPoint convertPoint = [self convertPoint:point toView:obj];
            hit = [obj hitTest:convertPoint withEvent: event];
            if (hit) {
                *stop = YES;
            }
        }];
        
        if (hit) {
            return hit;
        } else {
            return self;
        }
    } else {
        return nil;
    }
}

- (BOOL)pointInside:(CGPoint)point withEvent:(UIEvent *)event {
    CGFloat x1 = point.x;
    CGFloat y1 = point.y;
    
    CGFloat x2 = self.frame.size.width / 2;
    CGFloat y2 = self.frame.size.height / 2;
    
    double dis = sqrt((X1 - X2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
    
    if (dis <= self.frame.size.width / 2) {
        return YES;
    } else {
        return NO;
    }
}

事件响应

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event;
- (void)touchsMoved:(NSSet *)touches withEvent:(UIEvent *)event;
- (void)touchedEnded:(NSSet *)touches withEvent:(UIEvent *)event;