Android Studio Unknown attribute in xml and Namespace not found

Question

I recently got this warning in Layout and manifest files. I have attached those images below just check those in case for further clarification.

The pro

Answer 1

This is problem with Android studio caches.

most probably syncing the project with gradle files will help

If no, you can manually delete cached files located on $HOME/.AndroidStudio3.2/system/caches and rebuild your project.

UPDATE: Gradle sync cache isses fixed in android studio 3.5 version. Update android studio to latest version can help.