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

It is very simple. Delete .caches file:

1. Just close your AS.
2. Go to .AndroidStudio3.2 folder.
3. Delete the Caches file (path is: C:\Users\user\.AndroidStudio3.2\system)
4. Restart your AS.
5. Enjoy.