选择器是发送消息的机制，通过 @selector（方法名）或者 创建SEL 类型的变量来调用执行方法。

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//通过方法名创建选择器
        SEL sel=@selector(dogEat);
        
        Dog *xiaobai = [[Dog alloc]init];
        
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"  //告诉编译器不会造成内存泄漏
        if ([xiaobai respondsToSelector:sel]){ //判断对象所属类是否实现了selector中的方法
            NSLog(@"方法1");
        [xiaobai performSelector:sel]; //通过performSelector关键字，执行了选择器中的方法。
        }
    
        
        
//用方法名对的字符串对象生成选择器
        SEL sel2=NSSelectorFromString(@"dogBark:");
        
         if ([xiaobai respondsToSelector:sel2]){
             NSLog(@"方法2");
             [xiaobai performSelector:sel2 withObject:[NSNumber numberWithInt:5]];
        }

//用方法名的c语言字符串生成选择器
        SEL sel3 = sel_getUid("dogBark:");
        if ([xiaobai respondsToSelector:sel3]) {
            NSLog(@"方法3");
            [xiaobai dogBark:[NSNumber numberWithInt:4]];
        }
        
//获取选择器中的方法名
        NSLog(@"name = %@", NSStringFromSelector(sel)); //方法名字符串对象
        NSLog(@"name = %s", sel_getName(sel2));