Cannot Resolve Symbol Theme, Themeoverlay

I updated my android studio to latest version - 3.0.1. Since then it complains 'Cannot resolve symbol' for Theme and ThemeOverlay in the following lines of code. App runs fine but

Solution 1:

1)Close the project from the File menu.

2)Open the project again as existing Android Studio project.

This fix my problem.

Solution 2:

1. In the app/build.gradle remove the line responsible for the appcompat package (something like implementation 'com.android.support:appcompat-v7:27.1.1')
2. Perform the Gradle sync. It will break and show a lot of errors
3. Bring the original line back
4. Perform the Gradle sync once again

This will magically solve the problem that for no reason appeared in the 3.0.1

Solution 3:

Found Easiest Way

• Close project (File> Close Project)
• Import / Re-Open project again (NOT from Recent)

The error should be gone.

If(that_did_not_work)

• Open build.gradle, remove appcompact-v7 dependency and sync.
• Again add that dependency and sync.

Error Gone!

Solution 4:

Something got messed up on the indexing of the Project when you updated the version.

To fix go to the menu:

File -> Invalidate Caches/Restart

that will reopen and re-index the whole project, the error should be gone.

Solution 5:

I had this same error so i compared it to gradle file of another project which wasn't showing error. In your build.gradle(Module:app) under dependencies, add the following line:

implementation 'com.android.support:preference-v7:28.0.0'