Android Studio Cannot Resolve Symbol R

I just got this problem today when I opened an Android project with Android Studio. Basically, anywhere there’s a reference to R, for example R.layout.footer_view, Android Studio will complain that it cannot resolve symbol R.

The fix is surprisingly easy. All I need to do was running Gradle clean and Gradle build.

Ref: http://stackoverflow.com/questions/17054000/cannot-resolve-symbol-r-android-studio