Auto import not working for Android classes in Android studio

The problem was with android studio indexing.

Follow the steps..

Go to 'File' > 'Invalidate caches/restart'

Now the studio will shut down and restart. Now indexing begins. On completion of indexing you will find the Suggestion boxes with every possible suggestions.

For me, the problem was that "Show import popup" was not checked at File > Settings > Editor > General > Auto Import > Java.