git rm --cached ProjectFolder.xcodeproj/project.xcworkspace/xcuserdata/myUserName.xcuserdatad/UserInterfaceState.xcuserstate
git commit -m "Removed file that shouldn't be tracked"
然后在xcode commit的时候，UserInterfaceState.xcuserstate文件就会变成问号“？”状态，永远不要把它commit就可以了。
