addTarget:action:forControlEvents:实现原理？

addTarget:action:forControlEvents:实现原理是什么？另外如何自定义和触发event？

A control maintains an internal dispatch table: for each control event there is some number of target-action pairs, of which the action is a selector (the name of a method) and the target is the object to which that message is to be sent. When a control event occurs, the control consults its dispatch table, finds all the targer-action pairs associated with that control event, and sends each action message to the corresponding target.控件处理触屏事件，然后调用sendActionsForControlEvents，然后查找这个dispatch table，最后调用相关的方法

第一个不清楚第二个可以这样：接收、处理消息：[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(eventHandler:) name:@"eventType" object:nil ];-(void)eventHandler: (NSNotification *) notification{ NSLog(@"event triggered");}发送消息：[[NSNotificationCenter defaultCenter] postNotificationName:@"eventType" object:nil ];