cancelling 'com.example.myfirstapp.mainactivity activity launch'

1. Open Android Virtual Device Manager
2. select the AVD you use for your app.
3. Press the start button and wait for a new form to show up called (Launch Options).
4. Check the box "Wipe user data" and hit "Launch" button.

This should work.

--- OR ---

1. Open Android Virtual Device Manager
2. Delete the AVD you use for your app.
3. Create an new AVD.
4. Start your new AVD.

This should also work.