从异步block中取到数据

-(void)getTN{    //GCD 异步操作    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{        //异步现场 请求网络数据 耗时操作        AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];        manager.responseSerializer = [AFHTTPResponseSerializer serializer];        __block NSString * t =[[NSString alloc] init];        [manager GET:kURL_TN_Normal parameters:nil success:^(AFHTTPRequestOperation *operation, id responseObject) {            NSLog(@"Bloct >> tn ====  %@" , operation.responseString);            t = operation.responseString;            //返回主线程 拿到数据            dispatch_async(dispatch_get_main_queue(), ^{                t = operation.responseString;                NSLog(@"t ===== %@",t);                if ([_delegate respondsToSelector:@selector(getTNWithString:)]) {                    [_delegate getTNWithString:t];                }            });        } failure:^(AFHTTPRequestOperation *operation, NSError *error) {        }];    });}
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首先 ,你要把AFNetworking的处理方法  
放到全局队列里面 ,(应该是这样理解的吧)

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{....});
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然后,在这个代码块里,进行网络数据请求,

请求到网络数据之后, 立即在主线程更新数据

之后,使用代理 ,去别的ViewController里面传递要获取的数据,

over,下班