Android Studio - Cannot resolve symbol 'firebase'
<p>I'm currently upgrading an app to the new Firebase version. I followed the guide, included <code>classpath 'com.google.gms:google-services:3.0.0'</code> in the dependencies of my project build.gradle as well as <code>compile 'com.google.firebase:firebase-core:9.0.1'</code> among others in the dependencies of my module build.gradle and also <code>apply plugin: 'com.google.gms.google-services'</code> at the end of that file.</p>

<p>I get a "cannot resolve symbol 'firebase'" in my imports i.e. <code>import com.google.firebase.database.DatabaseReference;</code>. Those are not errors that appear when building, so this seems to be working, but they are visible in the code editor of Android Studio.</p>

<p>The imports worked just fine a couple of days ago (except for FirebaseAuth, which was under maintenance). I did not change anything about the code since then (except trying to upgrade to 9.0.2, which lead to the same result). The only thing I did was update some components of the Android SDK, but I can't remember which. The Android SDK as well as Google Repository and Google Play Services are of the newest version. Rebuilding, cleaning and invalidate caches / restart had no effect.</p>

<p>Any ideas how to fix this?</p>