AFNetworking-2 waitUntilFinished无法正常工作

Question

我知道还有另外一个类似的问题,但它适用于较旧版本的AFNetworking,并且无论如何都没有真正回答它.

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);
...

如果我运行它,我将在日志中看到的是:

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 = "";
}

本NSLog是后的waitUntilFinished火灾第一.我预计它会第二次开火.我错过了什么？

Answer 1

几点想法:

1. 问题是waitUntilFinished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);
   

   或者,您可以将它包装在您自己的并发NSOperation子类中,isFinished在AFHTTPRequestOperation完成块中发布,从而消除semaphore过程中的内容.

   注意,请确保指定completionQueue是否在主队列上执行信号量,因为如果没有,则AFNetworking默认将完成处理程序分派到主队列,并且您可以死锁.

2. 顺便说一句,你永远不应该阻止主队列(可怜的用户体验,你的应用程序可能被监视程序进程杀死等等),所以如果你是从主队列中执行此操作,我不鼓励使用其中任何一个waitUntilFinished或者信号.最好只在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);
   

听起来您希望让模型让UI在模型对象完成更新时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完成后要做什么(而不是使用waitUntilFinished或信号量使网络操作阻塞主队列).例如,假设您的模型有一些这样的方法:

- (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
}]

最后,您的代码可以使用AFNetworking使用的相同样式的完成块.如果您希望模型返回信息,您可以将其他参数添加到完成块本身,但我认为上面说明了基本概念.