UIApplication管理事件队列,当事件发生时,UIApplication把事件依次向下传,直到找到最适合的控件未知。
控件是通过- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event来寻找的。比如如果这个方法返回self,则不会再往下找了。。。
UIApplication -> [UIWindow hitTest:withEvent:] -> subView hitTest:withEvent........
判断原则:
- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)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 return fitView; } } // 循环结束,表示没有比自己更合适的view return self; }