How to Pause and Resume Downloading Files with ASI

I m using ASIHTTP Request sample source code for downloading urls. My question is that how to pause and resume the downloading files.

Please Help.

Deprecation Notice

ASIHTTP was deprecated around 2011, if you want network connectivity now, you should look up AFNetworking for ObjC or Alamofire for Swift, or stick to the native support:

For native support, in iOS 7 Apple added the NSURLSession, which can start download tasks (NSURLSessionDownloadTask), and these can be cancelled and restarted, check the method downloadTaskWithResumeData(_:) from NSURLSession, that has a very good explanation.

ASIHTTP is no longer needed, if you gotta are keeping a legacy app running, well, good luck.

Original Answer

Posted on 2011

ASI itself can resume a download from a file using [myASIRequest setAllowResumeForFileDownloads:YES];, check out the How-to-Use for an example.

Edit: Ok, there's no easy way to pause a download (a [myRequest pause] would be ideal). After reading and trying for a while, turns out that cancelling the request and resending it again is the only way.

For example, here's an example class I made:

@interface TestViewController : UIViewController <ASIHTTPRequestDelegate>
{
    ASIHTTPRequest *requestImage;
    UIImageView *imageViewDownload;
}

@property (nonatomic, retain) IBOutlet UIImageView *imageViewDownload;

- (IBAction)didPressPauseButton:(id)sender;
- (IBAction)didPressResumeButton:(id)sender;

To start (or restart) the download:

- (IBAction)didPressResumeButton:(id)sender
{
    if (requestImage)
        return;

    NSLog(@"Resumed");

    // Request
    requestImage = [ASIHTTPRequest requestWithURL:[NSURL URLWithString:@"http://www.myheadhealth.com/_IMAGES/cheese.jpg"]];

    // Using a temporary destination path just for show. 
    // Better pick a suitable path for your download.
    NSString *destinationDownloadPath = [NSTemporaryDirectory() stringByAppendingPathComponent:@"cheese.jpg"];
    NSString *temporaryDownloadPath = [NSTemporaryDirectory() stringByAppendingPathComponent:@"cheese.jpg-part"];

    requestImage.downloadDestinationPath = destinationDownloadPath;
    requestImage.temporaryFileDownloadPath = temporaryDownloadPath;
    requestImage.allowResumeForFileDownloads = YES;
    requestImage.delegate = self;
    [requestImage startAsynchronous];
}

In the exmaple above, I'm loading a random image of cheese I found, and storing a temporary download, and a full download.

Canceling the request will keep the contents of the temporary file intact, in fact, I made an UIImageView, and when pressing "Cancel" I could see a part of the downloaded file. If you want to try it out:

- (void)didPressPauseButton:(id)sender
{
    if (requestImage)
    {
        // An imageView I made to check out the contents of the temporary file.
        imageViewDownload.image = [UIImage imageWithContentsOfFile:requestImage.temporaryFileDownloadPath];

        [requestImage clearDelegatesAndCancel];
        requestImage = nil;

        NSLog(@"Canceled");
    }
}

- (void)requestFinished:(ASIHTTPRequest *)request
{
    imageViewDownload.image = [UIImage imageWithContentsOfFile:request.downloadDestinationPath];

    requestImage = nil;
}