Load Images One At A Time

问题:

So this code basically gets data from a server, creates an image, and then adds it to the view.

However, I would like it to update the view one at a time.

Right now, the view is updated with all the images at once after all are loaded.

I would like to update the view, everytime a new image is uploaded - This should happen in the addImage method, but instead, it is just waiting for all the images to load.

I tried using a dispatch_async to solve this problem, but it did not work.

So how do I load images one at at a time?

    AFJSONRequestOperation *operation =
        [AFJSONRequestOperation JSONRequestOperationWithRequest:request
                                                        success:^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) {
       //some code not displayed here that parses the JSON
       for (NSDictionary *image in images){
           if ([[image objectForKey:@"ContentType"] isEqualToString:@"image/png"]){
               NSString *imgLink = [[image objectForKey:@"MediaUrl"] JSONStringWithOptions:JKSerializeOptionPretty includeQuotes:NO error:nil];
               NSURL *url = [NSURL URLWithString:path];
               NSData *data = [NSData dataWithContentsOfURL:url];
               UIImage *img = [[UIImage alloc] initWithData:data cache:NO]
               dispatch_async(dispatch_get_main_queue(), ^{
                   [self addImage:img];
                   //This method adds the image to the view
                });
           }
       }
   }

---

Update: This is not a tableview, images are added as subviews to a UIView

回答1:

I believe you are looking for a form of lazy loading. Try this example: Apple Lazy Loading example

回答2:

[NSData dataWithContentsOfURL:url];

is a synch operation so you have to wait for each image one by one, a proper lazy loading implementation of the picture based on the url is the best solution, in the meantime you can try to do something like this

AFJSONRequestOperation *operation =
[AFJSONRequestOperation JSONRequestOperationWithRequest:request
                                                success:^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) {
                                                    //some code not displayed here that parses the JSON
                                                    for (NSDictionary *image in images){
                                                        if ([[image objectForKey:@"ContentType"] isEqualToString:@"image/png"]){
                                                            NSString *imgLink = [[image objectForKey:@"MediaUrl"] JSONStringWithOptions:JKSerializeOptionPretty includeQuotes:NO error:nil];
                                                            NSURL *url = [NSURL URLWithString:path];

                                        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
                                                                NSData *data = [NSData dataWithContentsOfURL:url];
                                                                UIImage *img = [[UIImage alloc] initWithData:data cache:NO]
                                                                dispatch_async(dispatch_get_main_queue(), ^{
                                                                    [self addImage:img];
                                                                    //This method adds the image to the view
                                                                });
                                                            })

                                                        }
                                                    }
                                                }

if you want to use this solution a recommend you to create your own concurrent queue rather than use the global_queue