How to get current running background session of NSURLSession while navigating view controller?

Question

I am developing an iOS application for downloading file from server (<10MB). I use NSURLSession and NSURLSessionDownloadTask for downloading.

My problem is that, the download view controller is not the rootViewController. When I turn back to the root view controller, I could see the download progress still work (from NSLog). But when I move to download view controller again, I could not see my label updated according to the progress. In this case, how could I get current running background session of NSURLSession to update my status label? Or any other solutions?

//Start downloading
-(void)startDownload: (NSString *)url{
    NSString *sessionId = MY_SESSION_ID;
    NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration backgroundSessionConfiguration:sessionId];
    sessionConfiguration.HTTPMaximumConnectionsPerHost = 1;
    self.session = [NSURLSession sessionWithConfiguration:sessionConfiguration
                                                    delegate:self
                                            delegateQueue:nil];
    self.downloadTask = [self.session downloadTaskWithURL:[NSURL URLWithString:url]];
    [self.downloadTask resume];
}

//Delegate
-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite{

    if (totalBytesExpectedToWrite == NSURLSessionTransferSizeUnknown) {
        NSLog(@"Unknown transfer size");
    }
    else{
        [[NSOperationQueue mainQueue] addOperationWithBlock:^{
            NSInteger percentage = (double)totalBytesWritten * 100 / (double)totalBytesExpectedToWrite;
            self.percentageLabel.text = [NSString stringWithFormat:@"Downloading (%ld%%)", (long)percentage];
            NSLog(@"Progress: %ld", (long)percentage);
        }];
    }
}

possible duplicate of [Add NSURLConnection loading process on UIProgressView](http://stackoverflow.com/questions/4255261/add-nsurlconnection-loading-process-on-uiprogressview) — novalagung, May 20 '14 at 03:53

Pravesh Singh · Answer 1 · 2014-07-25T10:20:50.033

This is what I did in my code and it worked:

[self performSelectorOnMainThread:@selector(setuploadStatus:) withObject:[NSString stringWithFormat:@"Upload %ld%%", (long)percentage] waitUntilDone:NO];

-(void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didSendBodyData:(int64_t)bytesSent totalBytesSent:(int64_t)totalBytesSent totalBytesExpectedToSend:(int64_t)totalBytesExpectedToSend {

    NSInteger percentage = (double)totalBytesSent * 100 / (double)totalBytesExpectedToSend;

    **[self performSelectorOnMainThread:@selector(setuploadStatus:) withObject:[NSString stringWithFormat:@"Upload %ld%%", (long)percentage] waitUntilDone:NO];**

    NSLog(@"Upload %ld%% ",(long)percentage);

}

-(void) setuploadStatus : (NSString *) setStat  {

    [_notifyTextLabel setText:setStat];

}

How to get current running background session of NSURLSession while navigating view controller?

1 Answers1