Using build variants

To explain how monetization with advertisements works on Android, we will add advertisements to our application, but before this, we will set up a build process that allows us to export two versions: the paid version and the free version. This strategy is commonly used in Play Store (having a free version with advertisements and a paid version without advertisements) so that all users can use the app for free, but the users that don't like advertisement and want to contribute with your app can always buy the paid version.

There is a second way of implementing this strategy, which is creating just one version and having the option of buying an add-on to remove the advertisements inside the app with In-App billing products. The downside of this way is that your app won't be listed in Play Store as a free app; it will be listed under "Offers in-App purchases", so there might be users who aren't comfortable with this or children that are not allowed...