使用.gitignore文件避免每次clean项目需要重新commit文件（XX.xcodeproj/project.xcworkspace/xcuserdata/XX.xcuserdatad/UserInterfaceState.xcuserstate），但是没有效果，网上查到需要执行：
git rm --cached XX.xcodeproj/project.xcworkspace/xcuserdata/XX.xcuserdatad/UserInterfaceState.xcuserstate
git commit -m "Removed file that shouldn't be tracked"
同时，在.gitignore文件中加入如下几行：
*.xcuserstate
project.xcworkspace
xcuserdata
UserInterfaceState.xcuserstate
project.xcworkspace/
xcuserdata/
UserInterface.xcuserstate