how to cancel the pending download task using NSURLSession in ios? - ios

Question

I am creating a iPhone app which download icons using NSURLSession & NSURLDownloadTask.
In this case i want to download only the visible cell icons, when i scrolled the table all pending downloadTask get canceled (i.e download task for non-visible cells is must cancel). For this i created a method terminateAllDownloads().
// terminateAllDownloadTask
-(void)terminateAllDownloads
{
NSArray *allDownloads = [self.iconDownloadInProgress allValues];
[allDownloads makeObjectsPerformSelector:#selector(cancelDownload)];
[self.iconDownloadInProgress removeAllObjects];
}
// cancelDownload
-(void)cancelDownload
{
[self.downloadTask cancel];
[self.session invalidateAndCancel];
}
and call this function in dealloc & didRecieveMemoryWarning methods of MasterViewController.m
// dealloc
-(void)dealloc
{
[self terminateAllDownloads];
}
// didReceiveMemeoryWarning
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
[self terminateAllDownloads];
}
but this method is not called single time. how should i do this ?
I am using the NSURLSession Delegates, not completion block
//code
-(void)startDownload
{
appDelgate = [[UIApplication sharedApplication] delegate];
self.fileName = self.appData.name;
self.iconURL = self.appData.iconURL;
NSURLSessionConfiguration *sessionConfig = [NSURLSessionConfiguration defaultSessionConfiguration];
sessionConfig.allowsCellularAccess = NO;
_session = [NSURLSession sessionWithConfiguration:sessionConfig delegate:self delegateQueue:nil];
self.downloadTask = [_session downloadTaskWithURL:[NSURL URLWithString:_iconURL]];
[_downloadTask resume];
}
-(void)cancelDownload
{
[self.downloadTask cancel];
[self.session invalidateAndCancel];
}
-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location
{
NSString *trimmedString = [_fileName stringByReplacingOccurrencesOfString:#" " withString:#""];
NSString *appIconDirectory = [[documentsDirectoryForAppIcons absoluteString] stringByAppendingPathComponent:#"appIcons"];
NSURL* destinationUrlForAppIcon = [[NSURL URLWithString:appIconDirectory] URLByAppendingPathComponent:[NSString stringWithFormat:#"%#%#",trimmedString, #".png"]];
NSError *error1;
if([appIconFileManager fileExistsAtPath:[destinationUrlForAppIcon absoluteString]])
{
[appIconFileManager removeItemAtPath:[destinationUrlForAppIcon absoluteString] error:NULL];
}
BOOL status = [appIconFileManager copyItemAtURL:location toURL:destinationUrlForAppIcon error:&error1];
if (status && !error1)
{
[appDelgate.downloadedIcons setValue:destinationUrlForAppIcon.path forKey:self.iconURL];
if(self.completionHandler)
{
self.completionHandler(destinationUrlForAppIcon);
}
}
else
{
NSLog(#"File copy failed: %#", [error1 localizedDescription]);
}
}

Answer 1

Probably you refer to self in the block passed to the NSURLSession producing a retain cycle.