Hacker News Reader

Comment by thathoo | Hacker News Reader

How is this better than SDWebImage or AFNetworking libraries? Any quick comparisons?

I have not seen SDWebImage. From what I can recall about AFNetworking (a fantastic library, by the way), it provides a category on UIImageView whose methods can download and display web images. I don't think it provides any help for loading images in a UITableViewController context. In other words, the app developer still needs to state what URL to load and when to load the images. With PFQueryTableViewController, you just state which image each cell should load, and the loading is managed by the controller.

SDWebImage provides a nifty category extension UIImageView+WebCache which provides a setImageWithURL:placeholderImage: method on UIImageViews and uses the SDWebImageCache to cache the images locally for you. It is excellent and I use it everywhere.

AFNetworking provides a similar category extension, but there is no obvious way to make it use an ondisk cache that survives app restarts, so its caching is not as useful as SDWebImage's.

I could be wrong, but as of iOS5, NSURLConnection does disk caching by default, and therefore so does AFNetworking. Source: http://petersteinberger.com/blog/2012/nsurlcache-uses-a-disk...

Yes, There is disk caching for NSURLConnection by default, but in my experience it does not cache it across app restarts, so each time the app starts again all the images have to be fetched all over again... SDWebImage gives the persistent disk caching I want.

If I'm misunderstanding what's happening please let me know...

NSURLCache does disk caching in iOS 5 and up, but only for http (no https) requests. Use SDURLCache if you want more options there.

Just glanced through SDWebImage's source code. Think this is quite similar to AFNetworking's UIImageView category. My comment below should also apply here.

In the Parse framework, the equivalent class is PFImageView. We chose to design our API differently; from my experience, I believe the assignment of the web image to load and the actual download of the images should be two different steps. This is evident in UITableViewController. In tableView:objectForRowAtIndexPath:, the app developer should know which URL to load, but we should not load the images at this point. Although you CAN achieve the same goal via the other two libraries' API, I feel strongly the API becomes more intuitive to use when the two steps are broken apart.

By the looks of it, Parse is still downloading the image as the table view scrolls (that would be only reasonable). The behavior of not displaying until the table stops moving would appear to be a shortcoming of Parse not executing its operation using NSRunLoopCommonModes. AFNetworking gets this right.

Hi Mattt, in PFQueryTableViewController, the downloading does not start until the scrolling stops. We chose to do this because we wanted the default loading behavior to be very passive. You could verify this is indeed the behavior from the animated gif - the network activity does not start until the table finished scrolling.

Reply on news.ycombinator.com