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

Ran into the same issue. I think that there's some specific bug related to this for Android Studio 3.2. My solution on Windows was to delete everything withing the cache/ folder in the .AndroidStudio3.2/ folder.

I tried everything that other's mentioned, sync gradle files, invalidate cache, removed the whole project and added it again. The only thing that worked for me was reinstalling the Android Studio. The second time that happened to me I decided to look for a better solution than reinstalling the whole Android Studio. Started playing with the cache files and figured out that deleting everything under the cache/ folder in the configuration folder of the Android Studio solved the problem.