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

100% Working

Do this two steps:

1. Go to folder where you android studio caches are located. I have android studio 3.6.3 For me it's C:\Users\User_folder\.AndroidStudio3.6\system\caches.
2. Go to the folder where you android studio projects are located. Open the project >then .idea folder and delete the caches. For me its C:\Users\User_folder\AndroidStudioProjects\Project_name\.idea\caches.