README.md

FirebaseUI for Cloud Firestore

FirebaseUI makes it simple to bind data from Cloud Firestore to your app's UI.

Before using this library, you should be familiar with the following topics:

• Structuring and querying data in Cloud Firestore.
• Displaying lists of data using a RecyclerView.

Using FirebaseUI to populate a RecyclerView

Data Model

Imagine you have a chat app where each chat message is a document in the chats collection of your database. In your app, you may represent a chat message like this:

public class Chat {
    
    private String mName;
    private String mMessage;
    private String mUid;
    private Date mTimestamp;

    public Chat() { } // Needed for Firebase

    public Chat(String name, String message, String uid) { 
        mName = name;    
        mMessage = message;    
        mUid = uid;
    }

    public String getName() { return mName; }

    public void setName(String name) { mName = name; }

    public String getMessage() { return mMessage; }

    public void setMessage(String message) { mMessage = message; }

    public String getUid() { return mUid; }

    public void setUid(String uid) { mUid = uid; }

    @ServerTimestamp
    public Date getTimestamp() { return mTimestamp; }

    public void setTimestamp(Date timestamp) { mTimestamp = timestamp; } 
}

A few things to note about this model class:

• The getters and setters follow the JavaBean naming pattern which allows Firestore to map the data to field names (ex: getName() provides the name field).
• The class has an empty constructor, which is required for Firestore's automatic data mapping.

For a properly constructed model class like the Chat class above, Firestore can perform automatic serialization in DocumentReference#set() and automatic deserialization in DocumentSnapshot#toObject(). For more information on data mapping in Firestore, see the documentation on custom objects.

Querying

On the main screen of your app, you may want to show the 50 most recent chat messages. In Firestore, you would use the following query:

Query query = FirebaseFirestore.getInstance()
        .collection("chats")
        .orderBy("timestamp")
        .limit(50);

To retrieve this data without FirebaseUI, you might use addSnapshotListener to listen for live query updates:

query.addSnapshotListener(new EventListener<QuerySnapshot>() {
    @Override
    public void onEvent(@Nullable QuerySnapshot snapshot,
                        @Nullable FirebaseFirestoreException e) {
        if (e != null) {
            // Handle error
            //...
            return;
        }

        // Convert query snapshot to a list of chats
        List<Chat> chats = snapshot.toObjects(Chat.class);

        // Update UI
        // ...
    }
});

If you're displaying a list of data, you likely want to bind the Chat objects to a RecyclerView. This means implementing a custom RecyclerView.Adapter and coordinating updates with the EventListener on the Query.

Fear not, FirebaseUI does all of this for you automatically!

Using the FirestoreRecyclerAdapter

The FirestoreRecyclerAdapter binds a Query to a RecyclerView. When documents are added, removed, or change these updates are automatically applied to your UI in real time.

First, configure the adapter by building FirestoreRecyclerOptions. In this case we will continue with our chat example:

// Configure recycler adapter options:
//  * query is the Query object defined above.
//  * Chat.class instructs the adapter to convert each DocumentSnapshot to a Chat object
FirestoreRecyclerOptions<Chat> options = new FirestoreRecyclerOptions.Builder<Chat>()
        .setQuery(query, Chat.class)
        .build();

Next create the FirestoreRecyclerAdapter object. You should already have a ViewHolder subclass for displaying each item. In this case we will use a custom ChatHolder class:

FirestoreRecyclerAdapter adapter = new FirestoreRecyclerAdapter<Chat, ChatHolder>(options) {
    @Override
    public void onBindViewHolder(ChatHolder holder, int position, Chat model) {
        // Bind the Chat object to the ChatHolder
        // ...
    }

    @Override
    public ChatHolder onCreateViewHolder(ViewGroup group, int i) {
        // Create a new instance of the ViewHolder, in this case we are using a custom
        // layout called R.layout.message for each item
        View view = LayoutInflater.from(group.getContext())
                .inflate(R.layout.message, group, false);

        return new ChatHolder(view);
    }
};

Finally attach the adapter to your RecyclerView with the RecyclerView#setAdapter(). Don't forget to also set a LayoutManager!

FirestoreRecyclerAdapter lifecycle

Start/stop listening

The FirestoreRecyclerAdapter uses a snapshot listener to monitor changes to the Firestore query. To begin listening for data, call the startListening() method. You may want to call this in your onStart() method. Make sure you have finished any authentication necessary to read the data before calling startListening() or your query will fail.

@Override
protected void onStart() {
    super.onStart();
    adapter.startListening();
}

Similarly, the stopListening() call removes the snapshot listener and all data in the adapter. Call this method when the containing Activity or Fragment stops:

@Override
protected void onStop() {
    super.onStop();
    adapter.stopListening();
}

If you don't want to manually start/stop listening you can use Android Architecture Components to automatically manage the lifecycle of the FirestoreRecyclerAdapter. Pass a LifecycleOwner to FirestoreRecyclerOptions.Builder#setLifecycleOwner(...) and FirebaseUI will automatically start and stop listening in onStart() and onStop().

Data and error events

When using the FirestoreRecyclerAdapter you may want to perform some action every time data changes or when there is an error. To do this, override the onDataChanged() and onError() methods of the adapter:

FirestoreRecyclerAdapter adapter = new FirestoreRecyclerAdapter<Chat, ChatHolder>(options) {
    // ...

    @Override
    public void onDataChanged() {
        // Called each time there is a new query snapshot. You may want to use this method
        // to hide a loading spinner or check for the "no documents" state and update your UI.
        // ...
    }

    @Override
    public void onError(FirebaseFirestoreException e) {
        // Called when there is an error getting a query snapshot. You may want to update
        // your UI to display an error message to the user.
        // ...
    }
};