NSURLSession Download Task- Progress Bar Issue

Question

I am working with a Non-ARC project, where i have to downloads video's, and once downloaded i will be displaying them. I am using NSURLSession for downloading it.

Problem is in Progress bar. I can download first two or three file correctly through progress bar when i start downloading fourth file, the progress bar is not updating properly but file s getting downloaded with last deleted file.

Getting crash on this when deleting and downloading again n again

Attempted to create a task in a session that has been invalidated

 - (void)startOrPauseDownloadingSingleFile : (UIButton *)sender
  {
    self.part_id_Value = self.part_id;
    m_Web getIconPathForAnimation:self.part_id];

     [UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
      NSURL *urlVideo=[NSURL URLWithString:self.NonInteractiveMP4URL];
      NSString *strlastcomponent=[urlVideo lastPathComponent];


      FileDownloadInfo *fdi = [[FileDownloadInfo alloc] initWithFileTitle:strlastcomponent andDownloadSource:[NSString stringWithFormat:@"%@",urlVideo]];



        if (!fdi.isDownloading)
        {
            // Check if should create a new download task using a URL, or using resume data.


            if (fdi.taskIdentifier == -1)
            {
             **Getting Crash Here**

                fdi.downloadTask = [self.session downloadTaskWithURL:[NSURL URLWithString:fdi.downloadSource]];
            }
            else
            {
                fdi.downloadTask = [self.session downloadTaskWithResumeData:fdi.taskResumeData];
            }

            // Keep the new taskIdentifier.
            fdi.taskIdentifier = fdi.downloadTask.taskIdentifier;

            // Start the download.
            [fdi.downloadTask resume];

            // Indicate for each file that is being downloaded.
            fdi.isDownloading = YES;
        }
    }

My Methods for downloading and updating progress bar -

- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite
 {
   double Progress = (double)totalBytesWritten / (double)totalBytesExpectedToWrite;
   NSLog(@"Progressview progress : %f",Progress);

if (totalBytesExpectedToWrite == NSURLSessionTransferSizeUnknown)
{
    NSLog(@"Unknown transfer size");
}
else
{
    [self performSelectorOnMainThread:@selector(updateProgress:) withObject:[NSString stringWithFormat:@"%f",Progress] waitUntilDone:NO];
 }
}

- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location
 {
 NSError *error;
 NSFileManager *fileManager = [NSFileManager defaultManager];
 NSString *destinationFilename = downloadTask.originalRequest.URL.lastPathComponent;
 NSURL *destinationURL = [self.docDirectoryURL URLByAppendingPathComponent:destinationFilename];

 if ([fileManager fileExistsAtPath:[destinationURL path]])
 {
    [fileManager removeItemAtURL:destinationURL error:nil];
 }
 BOOL success = [fileManager copyItemAtURL:location
                                    toURL:destinationURL
                                    error:&error];
 if (success)
  {
    [[NSOperationQueue mainQueue] addOperationWithBlock:^{
        NSLog(@"Download completed!");
        NSLog(@"destination file name : %@!",destinationFilename);
        NSLog(@"Part id of file name : %@!",self.part_id);
        [self performSelectorOnMainThread:@selector(updateProgress:) withObject:[NSString stringWithFormat:@"1.0"] waitUntilDone:NO];

        [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;

        NSString *filenameValue=[NSString stringWithFormat:@"%@",destinationFilename];
        NSString *hideExtension=[filenameValue substringToIndex:filenameValue.length-4];
        NSLog(@"filenameValue == %@", filenameValue);

        [self DBUpdateVideoURLStatus:self.part_id andFileName:filenameValue];
        [self DBInsertDownloads:self.part_id andFileName:filenameValue];

        UIAlertView *alert=[[UIAlertView alloc]initWithTitle:NSLocalizedString(@"Success", @"Success message") message:[NSString localizedStringWithFormat:@"%@ downloaded successfully!",hideExtension] delegate:self cancelButtonTitle:NSLocalizedString(@"Ok", @"Ok action") otherButtonTitles:nil];
        alert.tag = 1;
        [alert show];
        [alert release];
        [self.session finishTasksAndInvalidate];
    }];
 }
 else
  {
    NSLog(@"Unable to copy temp file. Error: %@", [error localizedDescription]);
  }
}

-(void)updateProgress:(id)progress
{
  float currentProgress = [progress floatValue];
  [self.downloadProgress setProgress:currentProgress animated:YES];
  [self.downloadProgress setNeedsDisplay];
  [self.tblview reloadData];
}

Answer 1

You said:

When i am trying to download and delete it and again download Attempted to create a task in a session that has been invalidated *** Terminating app due to uncaught exception 'NSGenericException', reason: 'Task created in a session that has been invalidated'

This is because you're calling finishTasksAndInvalidate, which tells NSURLSession that it should not only finish all queues tasks, but invalidate the session and not permit any more tasks. But there's another task to run, but you invalidated the session.

Bottom line, feel free to cancel a task, but don't invalidate the session object if you're going to start more tasks for the same session object.

Answer 2

Well I noticed one mistake:

mainQueue is processed on the main thread so you should not call performSelectorOnMainThread from the block performed on the main queue.

The standard pattern to get to the main thread at the end of a download task is to dispatch async onto main queue, rather than add an operation to the mainQueue as you have done.

Answer 3

Can you please try changing the following code and let us know what it results:

-(void)updateProgress:(id)progress
{
    dispatch_async(dispatch_get_main_queue(), ^{

        float currentProgress = [progress floatValue];
        [self.downloadProgress setProgress:currentProgress animated:YES];
        [self.downloadProgress setNeedsDisplay];

    });
    [self.tblview reloadData];
}