Failed to load NSMainNibFile

This post is only for the technically-minded out there

I spent some time tonight trying to figure out the cause of the above error, along with:

“Unknown class … in Interface Builder file.
*** Terminating app due to uncaught exception ‘NSUnknownKeyException’, reason: ‘[ setValue:forUndefinedKey:]:this class is not key value coding-compliant for the key …”

It turns out that the cause is fairly simple: the nib file was not included in the target. And for the second error, the .m file for my UIViewController subclass wasn’t included in the target. When you drag files into the project from another project, they’re not necessarily included in your target(s) automatically.

Be sure to click the file in the Groups pane, and then check the box(es) next to your desired build targets.