Question

我想使用async req来获取json数据，我已经通过syncrouns这样做，但现在要求是更改，但我无法将此代码修改为aync，因为我必须返回NSdata

+ (NSString *)stringWithUrl:(NSURL *)url
{

//    if(kShowLog)
        NSLog(@"%@", url);

    NSURL *newURL = [NSURL URLWithString:[NSString stringWithFormat:@"%@",url]];

    NSURLRequest *urlRequest = [NSURLRequest requestWithURL:newURL
                                                cachePolicy:NSURLRequestReloadIgnoringCacheData
                                            timeoutInterval:1];
    // Fetch the JSON response
    NSData *urlData;
    NSURLResponse *response;
    NSError *error;
//    NSOperationQueue *opQueue;

    // Make synchronous request
    urlData = [NSURLConnection sendSynchronousRequest:urlRequest returningResponse:&response error:&error];
    return [[NSString alloc] initWithData:urlData encoding:NSUTF8StringEncoding];
}

Answer 1

如果要继续返回数据，请在2.线程上调用stringWithUrl。（我会使用异步数据

dispatch_async(dispatch_get_global_queue(), ^{
     NSData *d = [self stringWithUrl:myURL];
     ...

     //update ui
     dispatch_sync(dispatch_get_main_queue(), ^{
         ...
     });
});

Answer 2

一种方法可行但是QUITE the hack（苹果公司一直在mac上使用旧苹果）将在等待时运行runloop：

hackisch ::但是如果完成块在同一个线程上运行，那么同步包装异步，那么runloop

    __block NSString *responseString = nil;
   [NSURLConnection sendAsynchronousRequest:[NSURLRequest requestWithURL:myurl] 
                                      queue:[NSOperationQueue mainQueue] 
                          completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
    responseString = [[NSString alloc] initWithData:Data encoding:NSUTF8StringEncoding];
    if(!responseString) {
         responseString = @"";
    }
   }];

   while(!responseString) { 
       [NSRunloop currentRunloop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:0.1];
   }

   return responseString;

Answer 3

您必须为此进程创建一个单独的线程，获取json数据的同步调用将阻止您的主线程。

我正在更改您的代码以执行异步操作以从Web服务获取json数据。

+ (void)stringWithUrl:(NSURL *)url
{

 dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
 dispatch_async(queue, ^{

    //    if(kShowLog)
    NSLog(@"%@", url);

    NSURL *newURL = [NSURL URLWithString:[NSString stringWithFormat:@"%@",url]];

    NSURLRequest *urlRequest = [NSURLRequest requestWithURL:newURL
                                                cachePolicy:NSURLRequestReloadIgnoringCacheData
                                            timeoutInterval:1];
    // Fetch the JSON response
    NSData *urlData;
    NSURLResponse *response;
    NSError *error;
    //    NSOperationQueue *opQueue;

    // Make synchronous request
    urlData = [NSURLConnection sendSynchronousRequest:urlRequest returningResponse:&response error:&error];

    dispatch_sync(dispatch_get_main_queue(), ^{

        //Here you have to put your code, which you wanted to get executed after your data successfully retrived.
        //This block will get executed after your request data load to urlData.
    });

 });

}

Answer 4

Asynchronous当时有什么问题，

     NSString *responseString;
     NSOperationQueue *operation = [[NSOperationQueue alloc]init];
       [NSURLConnection sendAsynchronousRequest:request queue:operation completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
           NSLog(@"data %@", data);
        responseString = [[NSString alloc] initWithData:Data encoding:NSUTF8StringEncoding];
       }];
     return responseString;

JSON异步请求

4 个答案: