How to know if AfNetworking has downloaded all the image - ios

Question

I think I am asking a silly question but just curious.
Is there any way to know if all the images are downloaded.
My motive behind this is that I want to invoke one function once all the images are downloaded.
I am using UIImageview setImageWithURL in a for loop
Thanks in Advance :)

Answer 1

You'll want to use UIImageView+AFNetworking's setImageWithURLRequest method. The success block is executed when the image has finished loading.
#param urlRequest The URL request used for the image request.
#param placeholderImage The image to be set initially, until the image request finishes. If `nil`, the image view will not change its image until the image request finishes.
#param success A block to be executed when the image request operation finishes successfully. This block has no return value and takes three arguments: the request sent from the client, the response received from the server, and the image created from the response data of request. If the image was returned from cache, the request and response parameters will be `nil`.
#param failure A block object to be executed when the image request operation finishes unsuccessfully, or that finishes successfully. This block has no return value and takes three arguments: the request sent from the client, the response received from the server, and the error object describing the network or parsing error that occurred.
*/
- (void)setImageWithURLRequest:(NSURLRequest *)urlRequest
placeholderImage:(UIImage *)placeholderImage
success:(void (^)(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image))success
failure:(void (^)(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error))failure;

Answer 2

Since setImageWithURL is asynchronous, it makes it a bit difficult to keep track of whether or not all the images have been downloaded. One solution that might work would be to use the setImageWithURLRequest:placeholderImage:success:failure: method, which allows you to execute code whenever the image URL request succeeds or fails.
Since you're running a for loop, you probably have a fixed number of images to run through. In this case, you can set up a property that keeps track of the images that have been downloaded in the success/failure blocks. When this value is equal to the number that you're wanting, then you can run some kind of logic (i.e. post a notification, delegation) to trigger that all downloads have been completed. (Or, if there were any failures, you can add some logic for retrying/post a message saying there was an error, etc.)
For example (assume numberOfImagesToDownload is some constant value set):
- (void)processImageForURL:(NSURL *)url {
// Assume `placeholderImage` is a reference to an image.
[imageView setImageWithURLRequest:[NSURLRequest requestWithURL:url]
placeholderImage:placeholderImage
success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) {
// Logic here to set the imageView's image (for the example's sake, assume
// we have access to the respective UIImageView.)
imageView.image = image;
// Hold onto a property to keep track of how many images you've downloaded,
// under the assumption that there's a set number of images you need to download.
// Since you're running this under a for loop, you could probably check if the
// for's max condition is equal to the number of downloaded images.
self.numberOfImagesDownloaded++;
if(self.numberOfImagesDownloaded == numberOfImagesToDownload) {
// All images have been downloaded.
}
}
failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error) {
// You can also keep track of which images failed, if that's important.
}];
}

Answer 3

You can queue your requests using NSOperationQueue and use KVO to observe the operations property of your queue, then you can tell if your queue has completed by checking for [queue.operations count] == 0.
Add a observer of the operations property:
[self.queue addObserver:self forKeyPath:#"operations" options:0 context:NULL];
Handle the event when operations count hits 0:
- (void) observeValueForKeyPath:(NSString *)keyPath
ofObject:(id)object
change:(NSDictionary *)change
context:(void *)context
{
if (object == self.queue && [keyPath isEqualToString:#"operations"])
{
if ([self.queue.operations count] == 0)
{
// Your downloads have completed
}
}
else
{
[super observeValueForKeyPath:keyPath
ofObject:object
change:change
context:context];
}
}
And you add your requests like this:
AFImageRequestOperation *imgRequest = [AFImageRequestOperation imageRequestOperationWithRequest:urlRequest success:^(UIImage *image) { }
[self.queue addOperation: imgRequest]
This is only a pseudocode. I haven't tested it but it should point you to the right direction.