A category on UIView that allows you to progressively download images. Leverages AFNetworking's image cache to make seamless image enhancements really easy.

Why is this useful?

It is common to download smaller images for use as thumbnails when rendering many records in a table view. When you visit the detail for a given page, you'd like to download a higher resolution image, but use the one we've already downloaded as a starting point, so the user doesn't get a flash of no content when the detail view controller loads.

This leverages AFNetworking's image cache, so all you need is a set of progressively enhanced URLs. It supports any number of requests, but you'll probably only use 2 (small/large).

Requirements

• iOS 6.0
• AFNetworking

Installation

TODO

Usage

Import the header:

#import "UIImageView+AFProgressiveDownload.h"

Prepare a list of URLs:

NSArray *urls = @[ smallUrl, largeUrl ];

Load it on the image view:

[self.imageView setImageProgressivelyWithImageURLs:progressiveURLS
                                      placeholderImage:self.placeholderImage
                                            completion:^(NSURL *imageURL, BOOL success, NSError *error, BOOL completed) {
                                                NSLog(@"Completed %@", imageURL);

                                                // just to make the effect more obvious
                                                sleep(1);
    }];

Demo

Check out the provided sample project for a live demo. Here's what it looks like:

It's hard to see with scaled down images, but the one on the right is retina resolution.

License

AFProgressiveImageDownload is provided under the MIT license. See LICENSE for specifics.

Attribution

This library is made possible by AFNetworking, which is doing all of the heavy lifting here. The demo project uses Creative Commons licensed images. Credits to Eugene Kukulka and WPZOOM.

Created as part of the Objective-C Hackathon on June 29th, 2013.