iPhoneアプリ開発でコードの補完ができなくなったとき。

参照：
http://stackoverflow.com/questions/5431501/xcode-4-code-sense-is-not-working

１．Close the project, leaving XCode still running.

２．Open XCode’s Organizer window, go to the Projects Tab, select the correct project, and hit the Delete button next to “Derived Data”.

３．Quit XCode.

４．Navigate to your project’s .xcodeproject file in Finder. Right-click, choose “Show Package Contents.”

５．Leave the project.pbxproj file, but delete the project.xcworkspace file, any .pbxuser files, and the entire userdata folder.

６．Open the project in XCode. You will see XCode riding high on the CPU usage for around 10-60 seconds, depending on the size of your project. The activity window will say “Indexing”

７．When your CPU spike returns to earth, code completion will be working again.