This is a legacy Firebase example (for SDK 2.x.x). You probably want one of the up-to-date examples.
This Android application demonstrates the use of the Firebase SDK to create a shared drawing canvas. It also demonstrates the use of Firebase's offline and disk persistence capabilities. These ensure that the app will continue to work even when experiencing intermittent connectivity loss and when the app is restarted. Multiple users can run the app and draw on the same or different canvases. Line segments are synchronized as the user draws them.
Update DrawingActivity and replace
https://android-drawing.firebaseio-demo.com with a reference to your Firebase.
The drawing and color-picking portions of this application are largely adapted from Google's ApiDemo application, which was shipped with a previous version of the Android SDK's sample code.
This example is intended to demonstrate how you can adapt single-user applications to be collaborative with the help of Firebase. Create your own Firebase app and incorporate these techniques into your own application!
When you keep a board in sync, its data will be kept up to date, even while you're looking at another board. For more information about how to use Firebase's offline capabilities in your app, see this section of our guide for Android developers.
You can do lots more with Firebase on Android. Check out our Android Quickstart guide to learn more.