[self performSelector:@selector(test:)withObject:nil afterDelay:1];
//延時1秒執行 方法將會在當前線程的Run Loop中根據afterDelay參數創建一個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];