How to get download progress in AFNetworking 2.0?

Question

I am using AFURLSessionManager to create a new download task:

AFURLSessionManager* manager = ...

NSProgress* p = nil;
NSURLSessionDownloadTask* downloadTask =
        [manager downloadTaskWithRequest:request
                                 progress:&p
                              destination:^NSURL*(NSURL* targetPath, NSURLResponse* response) {...}
                        completionHandler:^(NSURLResponse* response, NSURL* filePath, NSError* error) {...}
        ];
[downloadTask resume];

The file gets downloaded fine, however, how do I get progress notifications?

p is always set to nil. I've filed an issue for that.

I've also tried to call setDownloadTaskDidWriteDataBlock on the manager, and I do get progress notifications there but I receive them all grouped together after the file has been downloaded.

Seems like this area is still a bit buggy in AFNetworking 2.0

Any ideas?

Solution 1

You should observe the fractionCompleted property of your NSProgress object using KVO:

NSURL *url = [NSURL URLWithString:@"http://www.hfrmovies.com/TheHobbitDesolationOfSmaug48fps.mp4"];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
AFHTTPSessionManager *session = [AFHTTPSessionManager manager];
NSProgress *progress;
NSURLSessionDownloadTask *downloadTask = [session downloadTaskWithRequest:request progress:&progress destination:^NSURL *(NSURL *targetPath, NSURLResponse *response) {
    // …
} completionHandler:^(NSURLResponse *response, NSURL *filePath, NSError *error) {
    [progress removeObserver:self forKeyPath:@"fractionCompleted" context:NULL];
    // …
}];

[downloadTask resume];
[progress addObserver:self
            forKeyPath:@"fractionCompleted"
               options:NSKeyValueObservingOptionNew
               context:NULL];

Then add the observer method:

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    if ([keyPath isEqualToString:@"fractionCompleted"]) {
        NSProgress *progress = (NSProgress *)object;
        NSLog(@"Progress… %f", progress.fractionCompleted);
    } else {
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
    }
}

Of course, you should check keyPath and/or object parameters to decide if that's the object/property you want to observe.

You can also use the setDownloadTaskDidWriteDataBlock: method from AFURLSessionManager (from which AFHTTPSessionManager inherits) to set a block for receiving download progress updates.

[session setDownloadTaskDidWriteDataBlock:^(NSURLSession *session, NSURLSessionDownloadTask *downloadTask, int64_t bytesWritten, int64_t totalBytesWritten, int64_t totalBytesExpectedToWrite) {
    NSLog(@"Progress… %lld", totalBytesWritten);
}];

This AFNetworking method maps the URLSession:downloadTask:didWriteData:totalBytesWritten:totalBytesExpectedToWrite: method from NSURLSessionDownloadDelegate protocol to a more convenient block mechanism.

BTW, Apple's KVO implementation is severely broken. I recommend using a better implementation like the one proposed by Mike Ash with MAKVONotificationCenter. If you are interested in reading why Apple's KVO is broken, read Key-Value Observing Done Right by Mike Ash.

Solution 2

I faced a similar problem, and found a solution.

Check the link below: http://cocoadocs.org/docsets/AFNetworking/2.0.1/Categories/UIProgressView+AFNetworking.html

#import <AFNetworking/UIKit+AFNetworking.h>

and use the additional method available to your UIProgressView

setProgressWithDownloadProgressOfTask:animated:

How I did it:

NSURLSessionDownloadTask *downloadTask = [manager downloadTaskWithRequest:request  progress:nil destination:^NSURL *(NSURL *targetPath, NSURLResponse *response){
    NSURL *documentsDirectoryPath = [NSURL fileURLWithPath:[NSSearchPathForDirectoriesInDomains(NSDocumentationDirectory, NSUserDomainMask, YES) firstObject]];
    return [documentsDirectoryPath URLByAppendingPathComponent:[targetPath lastPathComponent]];
} completionHandler:^(NSURLResponse *response, NSURL *filePath, NSError *error){
    NSLog(@"File downloaded to: %@", filePath);

}];

[self.progressView setProgressWithDownloadProgressOfTask:downloadTask animated:YES];
[downloadTask resume];

Comments

[Miles]

Agreed. I'm not able to get the downloader to even work. It cancels immediately.

[TPoschel]

If you want to be iOS6/7 compliant, you should use AFHTTPRequestOperation. AFURLSessionManager only works on iOS 7. I've posted an answer showing how to get download progress using AFHTTPRequestOperation.

[Shmidt]

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFBackgroundDownloadTask fractionCompleted]: unrecognized selector sent to instance 0xd888b40'

[Sendoa]

The fractionCompleted property belongs to the NSProgress object.

[alejandromp]

Be aware that in KVO you should not call super if you handle the notification.

[Sendoa]

Thanks @alejandromp . I've just edited it. BTW, I recommend a better implementation of KVO like the one proposed by Mike Ash: github.com/mikeash/MAKVONotificationCenter.

[Cameron Lowell Palmer]

In general, you might use the pattern NSStringFromSelector(@selector(fractionCompleted)) instead of using compiler opaque strings like @"fractionCompleted".

[Everus]

missed typed NSUR should be NSURL also there is an error for "control reaches end of non-void block"

[Praveen-K]

How to add extra headers to AFHTTPSessionManager. Error Domain=NSURLErrorDomain Code=-1102 "You do not have permission to access the requested resource." UserInfo=0xb96ba30 NSLocalizedDescription=You do not have permission to access the requested resource. This is how i am doing [self.sessionManager.requestSerializer setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"]; [self.sessionManager.requestSerializer setValue:[NSString stringWithFormat:@"Bearer %@",authToken] forHTTPHeaderField:@"Authorization"]; but when i check the request header it shows as (null)

[Manav]

Note: You'll need to use setTaskDidSendBodyDataBlock for data tasks (instead of the setDownloadTaskDidWriteDataBlock mentioned in the answer).

[Aaron Vegh]

Might be helpful to note that the manager variable in this code snippet is an instance of AFURLSessionManager.

[Amin Negm-Awad]

@CameronLowellPalmer What is the advantage of generating the string at runtime? Except of the cases, where it is not possible to do so.

[Genevios]

Awesome example! Thanks!