updated 03:45 pm EDT, Wed July 20, 2011
Makes Lion mandatory
Shortly after Xcode 4 went missing from the Mac App Store, Apple has replaced it with an updated suite, Xcode 4.1. The software is used to develop apps for OS X and iOS, and in its new incarnation includes SDKs for both OS X Lion and iOS 4.3. It has also been made free, with the catch that the suite requires Lion to run.
In terms of improvements the v4.1 update adds Interface Builder support for Auto Layout and new Aqua controls, such as NSPopover. Like the updated versions of iTunes and iWork a fullscreen mode has been added, though this works only in the workspace, project and organizer windows. A project modernization function can be used to find and fix outdated build settings.
Other changes include custom key bindings for behaviors, source control enhancements for pushing, pulling, and managing remote servers, and finally assistant editor support for the display of generated assembly and preprocessed output. Xcode 4.1 is a 2.96GB download. As with Xcode 4, users must be a registered developer to submit apps to the Mac or iOS App Stores, or even test and deploy in the case of iOS.