social-network-app | An Android Social Network App | Networking library

If you just want to get a bunch of documents a single time (not listening to changes), then you just need to use the get() method on each DocumentReference that you want. Each of these calls to get() returns a Task whose listeners will be invoked with the results. A Task is like a Future or a JavaScript Promise - it's what the Play Services uses for async programming.

If you want to wait until all of the calls to get are done, simply collect all those Task objects in a List, then pass that to Tasks.whenAll() to know when everything is done. That will return another Task that's successful only after all the other tasks are successful. You can then reach into all the other tasks to get the document contents.

You should be aware also that the code you're using sets up listeners to changes in the documents, and they will continue to fire when the documents change at the server. If you don't remove those listener, you will incur extra data costs, and also leak the listeners.