Programming iOS 6, 3rd Edition

Clean

From time to time, during repeated testing and debugging, and before making a different sort of build (switching from Debug to Release, or running on a device instead of the Simulator), it is a good idea to clean your target. This means that existing builds will be removed and caches will be cleared, so that all code will be considered to be in need of compilation and the next build will build your app from scratch.

The first build of your app after you clean will take longer than usual. But it’s worth it, because cleaning removes the cruft, quite literally. For example, suppose you have been including a certain resource in your app, and you decide it is no longer needed. You can remove it from the Copy Bundle Resources build phase (or from your project as a whole), but that doesn’t remove it from your built app. Only cleaning will do that, because it removes the built app completely.

To clean, choose Product → Clean. For more complete cleaning, hold Option to get Product → Clean Build Folder.

In addition, Xcode stores builds and project indexes in ~/Library/Developer/Xcode/DerivedData. From time to time, with Xcode not running, I like to move the contents of that folder to the trash. This is effectively a massive and even more complete clean of every project that you’ve opened recently. Alternatively, to trash the folder in DerivedData for a single project from within Xcode, switch to the Projects tab of the Organizer window (Window → Organizer), select the project at the left, ...