ObjC中_cmd的用法

1.直接代码展示

(void)viewDidLoad
{
[super viewDidLoad];
    NSLog(@"%@ call",NSStringFromSelector(_cmd));
}

输出结果如下：
2018-05-17 10:33:35.583110+0800 CoreGraphicsDemo_Example[99368:13538878] viewDidLoad call

image.png

_cmd在Objective-C的方法中表示当前方法的selector，正如同self表示当前方法调用的对象实例。

//比如需要打印当前被调用的方法，可以在一个方法中添加：
NSLog(@"%@ call",NSStringFromSelector(_cmd));
//会输出类似
//2013-01-10 11:25:46.902 TDDataViewer[855:303] applicationDidFinishLaunching: call
//这样的内容。
 
//在cocos2d中，_cmd通常用于定时调用某个函数（schedule）
//比如下面方法利用_cmd能够不定时地调用某个函数
-(void) scheduleUpdates {
    // schedule the first update as usual
    [self schedule:@selector(irregularUpdate:) interval:1]; 
}
-(void) irregularUpdate:(ccTime)delta {
    // unschedule the method first [self unschedule:_cmd];
    // I assume you’d have some kind of logic other than random to determine 
    // the next time the method should be called
    float nextUpdate = CCRANDOM_0_1() * 10;
    // then re-schedule it with the new interval using _cmd as the selector
    [self schedule:_cmd interval:nextUpdate]; 
}

2.其他用法：

- (CustomNavigationControllerDelegate *)customDelegate
{
    return objc_getAssociatedObject(self, _cmd);
}

- (void)setCustomDelegate:(CustomNavigationControllerDelegate *)customDelegate
{
    objc_setAssociatedObject(self, @selector(customDelegate), customDelegate, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}