CODEWITHSUNDEEP
iosiphoneobjective-cmacoscocoa
Nik
Nik

Reputation: 9472

GCD cancel async block?

I have regular code for loading images in table view cells 

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
        NSImage *image = file.image;
        dispatch_async(dispatch_get_main_queue(), ^{
            imageView.image = image;
        });
    });

The problem is when I scroll too fast I can see that last block fires several times on same imageView. And that looks really weird. Is there any way to cancel all previously scheduled operations for one imageView (lets say they all will have unique id) before scheduling new one?

I mean, I want to be sure that only last scheduled operation should be executed and all all previously scheduled should be dropped. Is that possible by means of Grand Central Dispatch? Or I have to add my own atomic flags to imageView objects and check whether flags are set before calling imageView.image = image;

Upvotes: 2

Views: 5127

Answers (2)

Stephen Paul
Stephen Paul

Reputation: 2842

Someone already said it, but using [[NSOperationQueue mainQueue] cancelAllOperations]; to cancel operations has worked like a charm for me in when managing intense networking calls.

Upvotes: 2

Michał Banasiak
Michał Banasiak

Reputation: 960

To archieve it using GCD you have to use your own atomic flag.

But there is a better solution where you have cancellation of tasks out of the box. It is a NSOperationQueue.

You can read everything you need under this link: http://www.raywenderlich.com/19788/how-to-use-nsoperations-and-nsoperationqueues

Upvotes: 8

Related Questions