No reference documentation in Android Studio

问题

A new problem just popped up yesterday. When I hover over a method or press Ctrl-Q, I used to get documentation info for that particular method.

But now I just get (pressing Ctrl-Q on SharedPreferences.getLong()):

Following external urls were checked:
            http://developer.android.com/reference/android/content/SharedPreferences.html#getLong-java.lang.String-long-
            http://developer.android.com/reference/android/content/SharedPreferences.html#getLong(java.lang.String, long) 

    The documentation for this element is not found. Please add all the needed paths to API docs in Project Settings.
        android.content.SharedPreferences
        public abstract long getLong(String s, long l)

I googled a lot, but couldn't find an answer. Which paths do I need to add and where?