Often I’ll see an app incorporate a new UI implementation that really impresses me. Still being a learner, I always wonder how these elements are coded or put together — is it an image trick? Maybe a CGGradientLayer? How are they able to achieve so much speed? It’s times like these that it helps to get a small peek under the hood. Like Mac apps, iOS apps are bundled together basically as a zip file — you can actually change the IPA extension to ZIP and unarchive the app very easily. The limitation here is Xcode compresses (or ‘crushes’) the png’s used in an app to keep the file size down. Luckily, since iOS 3.2, the command line tool that compressed these images included the added functionality of decompressing them. Peter Boctor (of iDevRecipes) wrote a Ruby script called App Crush that would uncrush the png files (with instructions here) but it hasn’t been updated in about a year. Since then, Apple has changed how Xcode is deployed (through the App Store these days) and the location in which they put it. It’s very easy to update the Ruby script to find the new Xcode and several have. I wanted to make it just a tad easier and created an Applescript Droplet that allows you to drag the IPA onto it and uncrushes the png files. You can download it here. I’ve also made this version’s source available here. This is my first attempt at an AppleScript Droplet (which seems like a dying tech) so if you see something that could be done better, let me know!
If you don’t know the location of the IPA (app) you’d like to uncrush, open iTunes and click the apps tab, right click on the app you’d like and click “Reveal in Finder”
Drag IPA onto the App Uncrusher
It’ll take up to a few minutes to finish and you’ll have a folder called “APPNAME images” on your desktop that should be full of pngs.
Be ethical with this. Don’t steal another app’s images and call them your own.
In my recent post about reducing load time for iOS apps, I discussed the importance of a proper Default.png. In the past I’ve made my Default.png “splash screen” image manually from mock ups and screenshots from the simulator — it can be very tedious with mixed results.
There is another way.
Before I show you, you need to know something — it uses a private API function. What does that mean? You need to remove this code before you submit your app to the App Store or it will be rejected. Private APIs are functions not to be used by anyone but Apple. So without further ado:
That’s it. You should put this code somewhere in your viewDidLoad function before you load all (but after you load some) of your UI elements. You’ll have to be the judge of the appropriate timing. Once this function is run, it’ll store a PNG screenshot of your application in the following location: