AFNetworking-2 waitUntilFinished 不起作用

Question

我知道有another similar question，但它是针对旧版本的 AFNetworking 的，并且无论如何都没有真正回答。

我有以下代码：

AFHTTPRequestOperationManager* manager = [AFHTTPRequestOperationManager manager];
manager.securityPolicy.allowInvalidCertificates = YES;
manager.requestSerializer = [AFJSONRequestSerializer serializer];
[manager.requestSerializer setAuthorizationHeaderFieldWithUsername: currentUser() password: currentPassword()];
__block NSDictionary* response = nil;
AFHTTPRequestOperation* operation = [manager
    GET: @"https://10.20.30.40:8765/foobar"
    parameters: [NSDictionary dictionary]
    success:^(AFHTTPRequestOperation* operation, id responseObject){
        response = responseObject;
        NSLog(@"response (block): %@", response);
    }
    failure:^(AFHTTPRequestOperation* operation, NSError* error){
        NSLog(@"Error: %@", error);}
];
[operation waitUntilFinished];
NSLog(@"response: %@", response);
...

如果我运行这个，我会在我的日志中看到：

2013-12-09 09:26:20.105 myValve[409:60b] response: (null)
2013-12-09 09:26:20.202 myValve[409:60b] response (block): {
    F00005 = "";
    F00008 = "";
    F00013 = "";
}

NSLog 是 在 waitUntilFinished 之后首先触发的。我预计它会第二次开火。我错过了什么？

Answer 1

一些想法：

1. 问题在于waitUntilFinished 将等待核心网络操作完成，但不会等待success 或failure 完成块。如果要等待完成块，可以使用信号量：

   __block NSDictionary* response = nil;
   
   dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
   
   manager.completionQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
   
   AFHTTPRequestOperation* operation = [manager GET: @"https://10.20.30.40:8765/foobar"
                                         parameters: [NSDictionary dictionary]
                                            success:^(AFHTTPRequestOperation* operation, id responseObject){
                                                response = responseObject;
                                                NSLog(@"response (block): %@", response);
                                                dispatch_semaphore_signal(semaphore);
                                            }
                                            failure:^(AFHTTPRequestOperation* operation, NSError* error){
                                                NSLog(@"Error: %@", error);
                                                dispatch_semaphore_signal(semaphore);
                                            }];
   
   NSLog(@"waiting");
   dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
   // [operation waitUntilFinished];
   NSLog(@"response: %@", response);
   

   您也可以将其包装在您自己的并发 NSOperation 子类中，将 isFinished 发布到 AFHTTPRequestOperation 完成块中，从而消除过程中的 semaphore。

   注意，如果在主队列上执行信号量，请确保指定completionQueue 因为，如果没有，AFNetworking 默认将完成处理程序分派到主队列，您可能会死锁。

2. 顺便说一句，您永远不应该阻塞主队列（糟糕的用户体验，您的应用程序可能会被看门狗进程杀死等），所以如果您是从主队列执行此操作，我不鼓励使用waitUntilFinished 或信号量。最好从完成块中启动您需要的任何内容，让主队列在此异步网络操作正在进行时继续执行，例如：

   [activityIndicatorView startAnimating];
   
   AFHTTPRequestOperation* operation = [manager GET: @"https://10.20.30.40:8765/foobar"
                                         parameters: [NSDictionary dictionary]
                                            success:^(AFHTTPRequestOperation* operation, id responseObject){
   
                                                // do whatever you want with `responseObject` here
   
                                                // now update the UI, e.g.:
   
                                                [activityIndicatorView stopAnimating];
                                                [self.tableView reloadData];
                                            }
                                            failure:^(AFHTTPRequestOperation* operation, NSError* error){
   
                                                // put your error handling here
   
                                                // now update the UI, e.g.:
   
                                                [activityIndicatorView stopAnimating];
                                            }];
   
   // NSLog(@"waiting");
   // dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
   // // [operation waitUntilFinished];
   // NSLog(@"response: %@", response);
   

---

听起来你想让你的模型在模型对象完成更新后让 UI 进行任何必要的更新。因此，您可以使用自己的块参数，以便视图控制器可以告诉模型对象在完成后要做什么（而不是使用waitUntilFinished 或信号量来使网络操作阻塞主队列）。例如，假设你的模型有这样的方法：

- (void)updateModelWithSuccess:(void (^)(void))success failure:(void (^)(NSError *error))failure
{
    AFHTTPRequestOperationManager* manager = [AFHTTPRequestOperationManager manager];
    manager.securityPolicy.allowInvalidCertificates = YES;
    manager.requestSerializer = [AFJSONRequestSerializer serializer];
    [manager.requestSerializer setAuthorizationHeaderFieldWithUsername: currentUser() password: currentPassword()];
    AFHTTPRequestOperation* operation = [manager GET: @"https://10.20.30.40:8765/foobar"
                                          parameters: [NSDictionary dictionary]
                                             success:^(AFHTTPRequestOperation* operation, id responseObject){

                                                 // do your model update here

                                                 // then call the success block passed to this method (if any),
                                                 // for example to update the UI

                                                 if (success)
                                                     success();
                                             }
                                             failure:^(AFHTTPRequestOperation* operation, NSError* error){
                                                 NSLog(@"Error: %@", error);

                                                 // if caller provided a failure block, call that

                                                 if (failure)
                                                     failure(error);
                                             }];
}

然后您的视图控制器可以执行以下操作：

[modelObject updateModelWithSuccess:^{
    // specify UI updates to perform upon success, e.g.
    // stop activity indicator view, reload table, etc.
} failure:^(NSError *error){
    // specify any UI updates to perform upon failure
}]

最重要的是，您的代码可以使用 AFNetworking 使用的相同样式的完成块。如果您希望模型将信息传回，您可以向完成块本身添加其他参数，但我认为以上说明了基本思想。