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事件传递:响应链
当我们在设计应用的时候,很可能希望应用可以对事件做出动态响应。比如,一个触摸可能会发生在屏幕上不同的对象上,我们需要决定让哪个对象来对指定的事件作出响应,并且理解这个对象是如何接收这个事件的。
当发生了一个由用户生成的事件时,UIKit创建一个包含处理这个事件所需信息的event对象,之后它会将这个event对象放到当前活跃的app的事件队列中。对于touch事件,这个event对象是一个一系列touch集合的UIEvent对象。对于motion事件,这个事件由我们所使用的框架和我们想要处理的motion事件类型而决定。
event会沿着特定的路径进行传递,直到它被传送到可以处理它的对象那里。首先,UIApplication单例对象会从最顶层的队列中接收事件,然后将其分发下去以便对其进行处理。
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