直接撸代码

1. 看一下下面的输出log
   现在一个页面有很多请求, 有的时候, 需要等请求全部完成,才能去刷新页面,这样就用到队列,GCD, 下面就是一个例子

 dispatch_group_t group = dispatch_group_create();
        dispatch_queue_t queue = dispatch_queue_create(0, 0);
        dispatch_group_enter(group);
        dispatch_group_enter(group);
        dispatch_group_enter(group);
        dispatch_async(queue, ^{
            [NSThread sleepForTimeInterval:1.0];
            dispatch_async(dispatch_get_global_queue(0, 0), ^{
                [NSThread sleepForTimeInterval:1];
                NSLog(@"任务1 完成");
                dispatch_group_leave(group);
            });
        });
        
        dispatch_async(queue, ^{
             [NSThread sleepForTimeInterval:2.0];
             dispatch_async(dispatch_get_global_queue(0, 0), ^{
                 [NSThread sleepForTimeInterval:2];
                 NSLog(@"任务2 完成");
                 dispatch_group_leave(group);
             });
         });
        

        dispatch_async(queue, ^{
            [NSThread sleepForTimeInterval:3.0];
            dispatch_async(dispatch_get_global_queue(0, 0), ^{
               [NSThread sleepForTimeInterval:3];
               NSLog(@"任务3 完成");
               dispatch_group_leave(group);
           });
        });
    
        NSLog(@"开始执行");
        dispatch_group_notify(group, queue, ^{
            NSLog(@"全部完成");
        });
        NSLog(@"最后一步");