iPhone上NSOperationQueue中的AFNetworking同步操作

Question

我的应用程序是这样工作的： - 创建相册并拍照 - 将它们发送到我的服务器上 - 图片分析后得到答案/补充信息。

发送部分有问题。这是代码

@interface SyncAgent : NSObject <SyncTaskDelegate>

@property  NSOperationQueue* _queue;
-(void)launchTasks;

@end


@implementation SyncAgent

@synthesize _queue;

- (id)init
{
    self = [super init];
    if (self) {
        self._queue = [[NSOperationQueue alloc] init];
        [self._queue setMaxConcurrentOperationCount:1];
    }
    return self;
}

-(void) launchTasks {

    NSMutableArray *tasks = [DataBase getPendingTasks];

    for(Task *t in tasks) {
        [self._queue addOperation:[[SyncTask alloc] initWithTask:t]];
    }
}
@end

还有 SyncTask ：

@interface SyncTask : NSOperation

@property (strong, atomic) Task *_task;
-(id)initWithTask:(Task *)task;
-(void)mainNewID;
-(void)mainUploadNextPhoto:(NSNumber*)photoSetID;

@end

@implementation SyncTask

@synthesize _task;

-(id)initWithTask:(Task *)task {
    if(self = [super init]) {
        self._task = task;
    }
    return self;
}

-(void)main {

    NSLog(@"Starting task : %@", [self._task description]);
    // checking if everything is ready, sending delegates a message etc

    [self mainNewID];
}

-(void)mainNewID {

    __block SyncTask *safeSelf = self;

    [[WebAPI sharedClient] createNewPhotoSet withErrorBlock:^{
        NSLog(@"PhotoSet creation : error")
    } andSuccessBlock:^(NSNumber *photoSetID) {
        NSLog(@"Photoset creation : id is %d", [photoSetID intValue]);
        [safeSelf mainUploadNextPhoto:photoSetID];
    }];
}

-(void)mainUploadNextPhoto:(NSNumber*) photoSetID {

    //just admit we have it. won't explain here how it's done
    NSString *photoPath;

    __block SyncTask *safeSelf = self;

    [[WebAPI sharedClient] uploadToPhotosetID:photoSetID withPhotoPath:photoPath andErrorBlock:^(NSString *photoPath) {
        NSLog(@"Photo upload error : %@", photoPath);

    } andSuccessBlock:^(NSString *photoPath) {

        NSLog(@"Photo upload ok : %@", photoPath);
        //then we delete the file
        [safeSelf mainUploadNextPhoto:photoSetID];
    }];
}
@end

每一个网络操作都是通过这种方式使用 AFNetworking 完成的：

-(void)myDummyDownload:(void (^)(NSData * data))successBlock
{
    AFHTTPClient* _httpClient = [[AFHTTPClient alloc] initWithBaseURL:[NSURL URLWithString:@"http://www.google.com/"]];
    [_httpClient registerHTTPOperationClass:[AFHTTPRequestOperation class]];

    NSMutableURLRequest *request = [_httpClient requestWithMethod:@"GET" path:@"/" nil];
    [request setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];

    AFHTTPRequestOperation *operation = [_httpClient HTTPRequestOperationWithRequest:(NSURLRequest *)request
        success:^(AFHTTPRequestOperation *operation, id data) {
            if(dataBlock)
                dataBlock(data);
        } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
            NSLog(@"Cannot download : %@", error);
    }];

    [operation setShouldExecuteAsBackgroundTaskWithExpirationHandler:^{
        NSLog(@"Request time out");
    }];

    [_httpClient enqueueHTTPRequestOperation:operation];
}

我的问题是：我的连接是异步建立的，因此即使在SyncAgent 中使用[self._queue setMaxConcurrentOperationCount:1]，每个任务也会一起启动而无需等待前一个任务完成。

我需要同步执行每个连接吗？我认为这不是一个好主意，因为永远不应该以这种方式进行连接，而且我可能会在其他地方使用这些方法并且需要在后台执行它们，但我找不到更好的方法。有什么想法吗？

哦，如果我的代码中有任何错误/错字，我可以向您保证，当我在粘贴之前尝试对其进行总结时，它出现了，它现在可以正常工作。

谢谢！

PS：抱歉，我找不到更好的方法来解释问题。

编辑：我发现使用信号量更容易设置和理解：How do I wait for an asynchronously dispatched block to finish?

Answer 1

如果你对服务器有任何控制权，你真的应该考虑创建一个 API，允许你以任意顺序上传照片，以支持多个同时上传（这对于大批量可能会更快一些)。

但如果您必须同步执行操作，最简单的方法可能是将新请求排入请求的完成块中。即

// If [operations length] == 1, just enqueue it and skip all of this
NSEnumerator *enumerator = [operations reverseObjectEnumerator];
AFHTTPRequestOperation *currentOperation = nil;
AFHTTPRequestOperation *nextOperation = [enumerator nextObject]; 
while (nextOperation != nil && (currentOperation = [enumerator nextObject])) {
  currentOperation.completionBlock = ^{
    [client enqueueHTTPRequestOperation:nextOperation];
  }
  nextOperation = currentOperation;
}
[client enqueueHTTPRequestOperation:currentOperation];

Answer 2

以下代码对我有用，但我不确定它的缺点。用少许盐服用。

 - (void) main {

  NSCondition* condition = [[NSCondition alloc] init];  
  __block bool hasData = false;
  [condition lock];

  [[WebAPI sharedClient] postPath:@"url" 
                        parameters:queryParams 
                           success:^(AFHTTPRequestOperation *operation, id JSON) {
                             //success code
                             [condition lock];
                             hasData = true;
                             [condition signal];
                             [condition unlock];

                           } 
                           failure:^(AFHTTPRequestOperation *operation, NSError *error) {

                             //failure code

                             [condition lock];
                             hasData = true;
                             [condition signal];
                             [condition unlock];
                           }];

  while (!hasData) {
    [condition wait];
  }
  [condition unlock];

}