Question

I have this bit of code to download an mp3 from the server. All is set up with Table View parsing a podcast, and the link for the mp3 is the _entry.articleURL. After just a few minutes, the iPhone kills the connection, and I end up with just a small portion of the mp3 downloaded. Any ideas what may be causing this?

-(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;
}

The issue is that it seems the connectionDidFinishLoading keeps getting called, even if incomplete. Any thoughts?

Answer 1

Not sure why you are using beginBackgroundTaskWithExpirationHandler to do this work – its purpose is for a completely different task (doing a bit of work after your app gets moved to the background. Your usage of this while in the foreground is most likely the reason for your problems.

What I suggest you do is go poking around on github etc for a sample Concurrent NSOperation demo project, and use those to do your asynchronous NSURLConnections.

Also, you are updating a GUI element in a view in the callbacks. Keep in mind you must be on the main thread do work with UIKit. If you need to update something, just use a block and dispatch it to the main queue to do the updating.