Android Studio suddenly cannot resolve symbols

Question

Android Studio 0.4.2 was working fine and today I opened it and almost everything was red and the auto-completion had stopped working. I look at the imports and AS seems to

Answer 1

There is a far easier solution built into Android Studio, and it usually works for me without needing any brute force solution mentioned in other answers - so you should try this first:

click on the "gradle" symbol on the right side of Android Studio, and then on the "Refresh all Gradle projects" tool.