Ok, I'm not sure what I modified on project.pbxproj file. Here is the result, I've checked the app target build phrase Copy Bundle Resources and all the xib files are there. If I move the whole app DerivedData folder to trash, reset the iOS Simulator, then build it, the app works fine, also I found all the nib files are included in $/Build/Products/Debug-iphonesimulator/Foo.app/ (no localization for nib file). I ran it, the view controller related show very well.
If I don't clean the derived data folder, build & run the app at the second time, now here is the problem, all the xib related view/view controller will show blank or crash. I checked the nib files over there, all of them disappear, but the image resources still exist.
How did it do when build/copy the nib resources?
Another found: some temporarily files are generated in $/Build/Intermediates/.build/Debug-iphonesimulator/.build, if I clean the .build only, rebuild it, it works fine.
I could solve this by script to remove the .build when building every time, but still wonder why.
Environment: Xcode 6.1.1/6.1
Please, any suggestions are grateful, thanks!