NSObject中取消selector的方法

[self performSelector:@selector(test:)withObject:nil afterDelay:1];

//延时1秒执行 方法将会在当前线程的Run Loop中根据afterDelay参数创建一个Timer

[NSObject cancelPreviousPerformRequestsWithTarget:self];

//取消selector 方法

[self performSelector:@selector(test:)withObject:nil afterDelay:1];

[NSObject cancelPreviousPerformRequestsWithTarget:self selector:@selector(test:) object:nil];