How to tell if blocks in loop all have completed executing?

Question

I have a loop set up that downloads a series a images which I will later use for to animate using the `animationImages` property of `UIImageView`. I would like to know when all the blocks inside my loops have finished executing so I could begin the animation, and was wondering how I may be able to tell when they are finished completing? Thanks! ``` for (PFObject *pictureObject in objects){ PFFile *imageFile = [pictureObject objectForKey:@"image"]; NSURL *imageFileURL = [[NSURL alloc] initWithString:imageFile.url]; NSURLRequest *imageRequest = [NSURLRequest requestWithURL:imageFileURL]; [tokenImageView setImageWithURLRequest:imageRequest placeholderImage:nil success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) { [self.downloadedUIImages addObject:image]; //This is a mutableArray that will later be set to an UIImageView's animnationImages } failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error) { NSLog(@"Error %@", error); }]; } //When I k…

Accepted Answer

Create a dispatch group, in the for loop enter the group, in the completion block leave the group. Then you can use dispatch_group_notify to find out when all blocks have completed:

```
dispatch_group_t    group = dispatch_group_create();

for (PFObject *pictureObject in objects){

PFFile *imageFile = [pictureObject objectForKey:@"image"];
    NSURL *imageFileURL = [[NSURL alloc] initWithString:imageFile.url];
    NSURLRequest *imageRequest = [NSURLRequest requestWithURL:imageFileURL];

dispatch_group_enter(group);
    [tokenImageView setImageWithURLRequest:imageRequest placeholderImage:nil success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) {
        [self.downloadedUIImages addObject:image]; //This is a mutableArray that will later be set to an UIImageView's animnationImages
        dispatch_group_leave(group);
    } failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error) {
        NSLog(@"Error %@", error);
        dispatch_group_leave(group);
    }];

}

dispatch_group_notify(group, dispatch_get_main_queue(), ^{
    // do your completion stuff here
});
```

How to tell if blocks in loop all have completed executing?

Solution

Problem

Related problems