NSURL iPhone应用程序的连接下载在完成之前终止

Question

我有这段代码从服务器下载mp3。所有设置都使用Table View解析播客，而mp3的链接是_entry.articleURL。短短几分钟后，iPhone终止连接，最终我只下载了一小部分mp3。任何想法可能造成这种情况？

-(void)didSelectRowAtIndexPath 
{  RSSEntry *entry = [_allEntries objectAtIndex:indexPath.row]; 

      self.nameit = entry.articleTitle; 
      NSURL *url = [NSURL URLWithString:entry.articleUrl];  
      NSURLRequest *theRequest = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestReloadIgnoringLocalCacheData timeoutInterval:60]; 
      __block NSURLConnection *connection = [NSURLConnection connectionWithRequest:theRequest delegate:self]; 

      UIApplication *application = [UIApplication sharedApplication]; //Get the shared application instance 

      __block UIBackgroundTaskIdentifier background_task; //Create a task object 

      background_task = [application beginBackgroundTaskWithExpirationHandler:^{ 
       // This code gets called when your app has been running in the background too long and the OS decides to kill it 
       // You might want to cancel your connection in this case, that way you won't receive delegate methods any longer. 
       [connection cancel]; 
       [application endBackgroundTask: background_task]; //Tell the system that we are done with the tasks 
       background_task = UIBackgroundTaskInvalid; //Set the task to be invalid 

       //System will be shutting down the app at any point in time now 
      }]; 

      self.backgroundTaskIdentifier = background_task; 
      if (connection) { 
       receivedData = [[NSMutableData data] retain]; 
       self.thetable = tableView; 
       self.thepath = indexPath; 
      } 
      else { 
       UIAlertView *cancelled = [[UIAlertView alloc] initWithTitle:@"Download Failed" message:@"Please check your network settings, and then retry the download." delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil]; 
       [cancelled show]; 
       [cancelled release]; 
      } 
} 

- (void) connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response { 
[UIApplication sharedApplication].networkActivityIndicatorVisible = YES; 
progress.hidden = NO; 
downloadInProgress = YES; 
RSSEntry *entry = [_allEntries objectAtIndex:thepath.row]; 

self.nameit = entry.articleTitle; 
downloadlabel.text = [NSString stringWithFormat:@"%@", nameit]; 
[thebar addSubview:downloadlabel]; 
[receivedData setLength:0]; 
expectedBytes = [response expectedContentLength]; 
} 

- (void) connection:(NSURLConnection *)connection didReceiveData:(NSData *)data { 
[receivedData appendData:data]; 
float progressive = (float)[receivedData length]/(float)expectedBytes; 
[progress setProgress:progressive]; 


} 

- (void) connection:(NSURLConnection *)connection didFailWithError:(NSError *)error { 
[UIApplication sharedApplication].networkActivityIndicatorVisible = NO; 
[connection release]; 
UIAlertView *connectionfailed = [[UIAlertView alloc] initWithTitle:@"Download Failed" message:@"Please check your network settings, and then retry the download." delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil]; 
[connectionfailed show]; 
[connectionfailed release]; 
progress.hidden = YES; 
downloadInProgress = NO; 
[downloadlabel removeFromSuperview]; 
[thetable deselectRowAtIndexPath:thepath animated:YES]; 
[[UIApplication sharedApplication] endBackgroundTask:self.backgroundTaskIdentifier]; 
self.backgroundTaskIdentifier = UIBackgroundTaskInvalid; 
[connection release]; 



} 

- (NSCachedURLResponse *) connection:(NSURLConnection *)connection willCacheResponse:(NSCachedURLResponse *)cachedResponse { 
return nil; 
} 

- (void) connectionDidFinishLoading:(NSURLConnection *)connection { 
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 

NSString *documentsDirectory = [paths objectAtIndex:0]; 
NSString *pdfPath = [documentsDirectory stringByAppendingPathComponent:[nameit stringByAppendingString:@".mp3"]]; 
NSLog(@"Succeeded! Received %d bytes of data",[receivedData length]); 
[UIApplication sharedApplication].networkActivityIndicatorVisible = NO; 
[receivedData writeToFile:pdfPath atomically:YES]; 
progress.hidden = YES; 
downloadInProgress = NO; 
[downloadlabel removeFromSuperview]; 

[thetable deselectRowAtIndexPath:thepath animated:YES]; 

[[UIApplication sharedApplication] endBackgroundTask:self.backgroundTaskIdentifier]; 
self.backgroundTaskIdentifier = UIBackgroundTaskInvalid; 
} 

问题是，似乎connectionDidFinishLoading一直在调用，即使不完整。有什么想法吗？

Answer 1

不确定为什么你使用beginBackgroundTaskWithExpirationHandler来完成这项工作 - 它的目的是完成一个完全不同的任务（在你的应用程序移动到后台后做一些工作，在前台使用这个工作很可能你做你的问题的原因。

我所说的其实是走在github等打交道了一个样本并行的NSOperation示范项目，并使用它们做你的异步NSURLConnections。

此外，要更新GUI请注意，您必须在主线程上使用UIKit，如果您需要更新某些内容，只需使用一个块并将其分派到主队列中进行更新。