activity function does not exist code example

Example: android error activity class does not exist

SOLUTION:

Sometimes when testing on a device, the app doesn't uninstall properly. 
To verify and fix this:

1.Go to Settings.
2.Go to Apps.
3.Select your app. (here, you can verify that your app is not uninstalled properly).
4.Open the overflow menu on the top right and select Uninstall for all users.
Done. Try to install then launch your app again.