in chapter 3 on the book under topic Applying themes to an activity.
When i tried to add android:theme="@android:style/Theme.Material"
showed 2 warning. After ignoring warning i ran the app then it kept on crashing.
warning 1:App is not indexable by Google Search; consider adding at least one Activity with an ACTION-VIEW intent filter.
warning 2:On SDK version 23 and up, your app data will be automatically backed up and restored on app install. Consider adding the attribute android:fullBackupContent to specify an @xml resource which configures which files to backup.