`Unresolved reference: android` on new Flutter project

Question

My first Flutter app seems to be debugging okay so far on my phone, but all of a sudden I'm seeing this error in my android/app/src/main/kotlin/my.appname.whatever/MainActivity file (screenshot below).

And when I rollover the onCreate, it shows this: Cannot access class 'android.Os.Bundle'. Check your module classpath for missing or conflicting dependencies.

I'm using AndroidStudio 3.2.1

While trying to get Firebase going, I changed the version of this (it was 1.2.17 I think, but had a warning about it being different than the IDE, so I changed it to what it suggested and the warning went away). Even after trying to change it back, I'm still getting the warning below.

buildscript { ext.kotlin_version = '1.3.11'

I assume this is something simple, but for someone very new to Android/Flutter...etc, I just don't have a clue where to look for the Unresolved reference: android, nor have any idea what I did to make it show up.

Answer 1

In my case, File -> Invalidate Caches / Restart worked. When Android Studio started back up, the issue was gone. Doesn't really answer the "why", but... it worked.

Answer 2

Configure to the project SDK to the appropriate API level as per your project will solve your issue(shown in the dialog after clicking Setup SDK at right corner).