Android Studio not recognizing Facebook SDK

Question

In build.gradle:

compile 'com.facebook.android:facebook-android-sdk:[4,5)'

In my code:

import com.facebook.AccessToken;
import com.facebook.AccessTokenTracker;
import com.facebook.login.LoginManager;

I don't think this was an issue before, but all of the sudden today it's saying "cannot resolve symbol" for all of the import statements and so lots of things in my code are now wrongly marked as errors, even though when I run my app it works fine. What could be causing this?

Answer 1

tools>android>sync project files with gradle files