In case that the ignored file kept showing up in the untracked list, you may use git clean -f -d
to clear things up.
1.
git rm --cached {YourProjectFolderName}.xcodeproj/project.xcworkspace/xcuserdata/{yourUserName}.xcuserdatad/UserInterfaceState.xcuserstate
2.
git commit -m "Removed file that shouldn't be tracked"
3.
WARNING first try git clean -f -d --dry-run
, otherwise you may lose uncommited changes.
Then:
git clean -f -d