Initiating Background transfer service in background fetch ios

Question

My objective is to send data/image to the server when the app is in background. From iOS7, we can do this using background fetch. But the background fetch only offers 30 sec time limit. The data which I am sending to the server may take longer time since it has more images. While googling I came across Background Transfer Service which offers unlimited time to upload/download data in the background. Is it possible to initiate the background transfer service in the background fetch code? If so how to handle it.

Answer 1

Whenever you want to start your upload/download (in your case during your 30secs of background fetch) execute the following lines:

        NSString *downloadURLString = //Your link here;
        NSURL* downloadURL = [NSURL URLWithString:downloadURLString];

        NSURLRequest *request = [NSURLRequest requestWithURL:downloadURL];


        // Create a background session
        static NSURLSession *session = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        NSString *identifier = @"com.yourcompany.yourapp";
        NSURLSessionConfiguration* sessionConfig = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:identifier];

        session = [NSURLSession sessionWithConfiguration:sessionConfig delegate:self delegateQueue:nil];
    });


        //Init a NSURLSessionDownloadTask with the just-created request and resume it
        NSURLSessionDownloadTask *task = [session downloadTaskWithRequest:request];
        [task resume];

    });

Also, don't forget to implement those delegate methods:

- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
                              didFinishDownloadingToURL:(NSURL *)location;

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


- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
                                      didResumeAtOffset:(int64_t)fileOffset
                                     expectedTotalBytes:(int64_t)expectedTotalBytes;

For a detailed sample, have a look at this sample app