Cmake Xcode project storyboard can not be loaded

I have been learning how to use CMake to generate a Xcode project. I found a nice example from http://ift.tt/1cDIfBJ. When I generate Xcode project from this testApp. I always experienced "The document "MainStoryboard_***.storyboard" could not be opened. Unrecognized file content"

I have tried that I could open MainStoryboard_***.storyboard from Xcode if I only open this storyboard without open *.xcodeproj file. I have tried to change configuration in the info.plist and cmakelists.txt files, I didn't find a solution yet.

I wonder if someone experienced this issue before,