Error when launching project in xcode 6.1.1 with "FacebookSDK / FacebookSDK.h" not found

The error when running a project in xcode 6.1.1 with "FacebookSDK / FacebookSDK.h" was not found, although it works fine in xcode 6.1.

I got this problem when I sifted through a new mac mini with Yosemite OS

Please help me out of this problem.

Thanks for any help.