如何用GCD同步若干个异步调用

我们是工程师 ——加油 ！.jpg

• 为了方便观看，我将队列、和组的命名都加上了YG后缀

-(void)test
{
    //获取全局并发队列
    dispatch_queue_t queueYG = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

    // 创建队列组
    dispatch_group_t groupYG = dispatch_group_create();

// ----------往队列组中添加耗时操作  1.  2.  3.---------
    dispatch_group_async(groupYG, queueYG, ^{

        NSLog(@"线程：%@--加载图片1", [NSThread currentThread]);
        });

    dispatch_group_async(groupYG, queueYG, ^{

      NSLog(@"线程：%@--加载图片2", [NSThread currentThread]);;
    });

    dispatch_group_async(groupYG, queueYG, ^{

        NSLog(@"线程：%@--加载图片3", [NSThread currentThread]);
    });
//--------------------    ------------------

// 当并发队列组中的任务执行完毕后才会执行这里的代码
    dispatch_group_notify(groupYG, dispatch_get_main_queue(), ^{

      NSLog(@"线程：%@--合并图片", [NSThread currentThread]);
    });

}

当耗时操作是异步执行的工具，比如像AFNetWorking等框架，上边的方法就不灵了，这是我们可以使用下面的方法；

-(void)test
{
    //获取全局并发队列
    dispatch_queue_t queueYG = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    
    // 创建队列组
    dispatch_group_t groupYG = dispatch_group_create();
    
    // ----------往队列组中添加耗时操作  1.  2.  3.---------
    dispatch_group_enter(groupYG);
    dispatch_group_async(groupYG, queueYG, ^{
        [MLNetWork postWithURLString:@"https://api.joint-think.com/api/home/searchlog" parameters:@{@"userid":@"2"} success:^(NSDictionary *dic) {
    
            NSLog(@"111111");
            dispatch_group_leave(groupYG);
        } failure:^(NSError *error) { }];
        
    });
    
    dispatch_group_enter(groupYG);
    dispatch_group_async(groupYG, queueYG, ^{
        [MLNetWork postWithURLString:@"https://api.joint-think.com/api/home/searchlog" parameters:@{@"userid":@"2"} success:^(NSDictionary *dic) {
            
            NSLog(@"22222");
            dispatch_group_leave(groupYG);
        } failure:^(NSError *error) { }];
    });
    
    dispatch_group_enter(groupYG);
    dispatch_group_async(groupYG, queueYG, ^{
        [MLNetWork postWithURLString:@"https://api.joint-think.com/api/home/searchlog" parameters:@{@"userid":@"2"} success:^(NSDictionary *dic) {
            
            NSLog(@"333333");
            dispatch_group_leave(groupYG);
        } failure:^(NSError *error) {  }];
    });
    
    // 当并发队列组中的任务执行完毕后才会执行这里的代码
    dispatch_group_notify(groupYG, dispatch_get_main_queue(), ^{
        
        NSLog(@"刷新UI");
    });
    
}