How to Empty Caches and Clean All Targets Xcode 4 and later

Command-Option-Shift-K to clean out the build folder. Even better, quit Xcode and clean out ~/Library/Developer/Xcode/DerivedData manually. Remove all its contents because there's a bug where Xcode will run an old version of your project that's in there somewhere. (Xcode 4.2 will show you the Derived Data folder: choose Window > Organizer and switch to the Projects tab. Click the right-arrow to the right of the Derived Data folder name.)

In the simulator, choose iOS Simulator > Reset Content and Settings.

Finally, for completeness, you can delete the contents of /var/folders; some caching happens there too.

WARNING: Deleting /var/folders can cause issues, and you may need to repair or reinstall your operating system after doing so.

EDIT: I have just learned that if you are afraid to grapple with /var/folders/ you can use the following command in the Terminal to delete in a more targeted way:

rm -rf "$(getconf DARWIN_USER_CACHE_DIR)/org.llvm.clang/ModuleCache"

EDIT: For certain Swift-related problems I have found it useful to delete ~/Library/Caches/com.apple.dt.Xcode. You lose a lot when you do this, like your spare copies of the downloaded documentation doc sets, but it can be worth it.

I found another way in addition to command+option+shift+K. In XCode 4.2 there is an organizer that can be opened from top-right icon. You can clean all archives and saved project options from there. This helped my situation (I was seeing old removed files in the mainBundle).

Command-Option-Shift-K should do it. Alternatively, go to product menu, press the option key, now the option "Clean" will change to "Clean Build Folder ..." select that option.

In addition to doing the following, you may experience this issue if your app's Storyboard's files are localized. First, do each of these:

• Clean Build
• Reset Simulator
• Restart Xcode
• Delete your DerivedData folder in ~/Library/Developer/Xcode/DerivedData
• Restart Computer

What finally worked for me was re-generating the storyboard localization files and deleting the English localization (which was unneeded because the Base Locale is English). To reload your Storyboard strings, see this answer on StackOverflow.

I had noticed that the non-text parts of my Storyboard were being updated, but not the localized text. If you have a localization in your app, I would recommend checking to make sure your localizations are updated (even if they're .strings files).