ios - AFNetworking-2 waitUntilFinished无法正常工作

我知道有another similar question，但是它是针对AFNetworking的较旧版本的，反正并没有真正回答。

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);
...

如果运行此命令，我将在日志中看到:

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之后的waitUntilFinished首先触发。我希望它能排第二。我想念什么？

最佳答案

有两个想法:

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，可以使用信号灯:

__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自己的并发NSOperation子类中，将isFinished张贴在AFHTTPRequestOperation完成块中，从而消除该过程中的semaphore。

注意，如果在主队列上进行信号量，请确保指定completionQueue因为在没有这种情况的情况下，AFNetworking默认将完成处理程序分派(dispatch)到主队列，并且您可能会死锁。

顺便说一句，您永远不应阻塞主队列(UX较差，您的应用可能会被看门狗进程杀死，等等)，因此，如果您从主队列中执行此操作，则我不建议您使用waitUntilFinished或信号量。最好只在完成模块中启动所需的任何内容，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);

听起来您想让模型对象完成更新后，让模型让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 View Controller 可以告诉模型对象完成后的操作(而不是使用waitUntilFinished或信号量使网络操作阻止主队列)。例如，假设您的模型具有如下所示的方法:

- (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 View Controller 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，您的代码可以使用与AFNetworking使用的样式相同的完成块。如果希望模型将信息传递回去，则可以将其他参数本身添加到完成模块中，但是我想上面的示例说明了基本思想。