Xcode 4: Creating a UIView xib, not properly connecting

I got into a similar state just today. It was very odd: I could attach any XIB (new or existing) to any already-existing ViewController class in the project, but I could not create a new ViewController and have it attach properly to any XIB. The "assistant" functionality didn't work, nor did the IB-to-headerfile-connection functionality.

Closing the project and re-opening did not fix it.
Quitting XCode and restarting did not fix it.
Creating a new project and testing the functionality worked fine, which led me to believe there was something corrupt in some cache somewhere.

My solution

• Close your project.
• Go to the ~/Library/Developer/XCode/DerivedData folder and REMOVE all subfolders there referencing the project you are working on.
• Open your project in XCode. The problem should be fixed now.

Incidentally, just running a full clean did not seem to clear things up. I had to trash the derived data. I'm certain I got into this position because of git games I was playing, but I had no idea how to get out, because even switching back to earlier git revisions didn't help. (That was a big clue also that it was something untracked by the project itself.)

This might not work for your specific issue, but occasionally I get that error when working with newly created nibs. Deleting and recreating the nibs and View Controllers with the same names as before didn't resolve the issue, but relaunching Xcode did.

I just had this problem and restarting Xcode did not fix it. I removed the class files from the project then added them back in and it started working.