处理unrecognized selector 这个方法 利用runtime 机制当中的消息转发机制
拯救报错三步
1Method resolution
objc+resolveInstanceMethod:+resolveClassMethod:
Message Forwarding
2Fast forwarding
-forwardingTargetForSelector:Runtime nilselfNormal FowardingFastNSInvocation
3Normal forwarding
RuntimenilRuntime-doesNotRecognizeSelector:RuntimeNSInvocation-forwardInvocation: