Firebase UI for Realtime Database #

Firebase UI enables you to easily integrate your application UI with your Realtime database.

Installation #

flutter pub add firebase_database
flutter pub add firebase_ui_database

Usage #

Import the Firebase UI for Realtime Database package.

import 'package:firebase_ui_database/firebase_ui_database.dart';

Infinite scrolling #

Infinite scrolling is the concept of continuously loading more data from a database as the user scrolls through your application. This is useful when you have a large datasets, as it enables the application to render faster as well as reducing network overhead for data the user might never see.

Firebase UI for Realtime Database provides a convenient way to implement infinite scrolling using the Realtime Database database with the FirebaseDatabaseListView widget.

At a minimum, the widget accepts a Realtime Database query and an item builder. As the user scrolls down (or across) your list, more data will be automatically fetched from the database (whilst respecting query conditions such as ordering).

To get started, create a query and provide an item builder. For this example, we'll display a list of users from the users collection:

final usersQuery = FirebaseDatabase.instance.ref('users').orderByChild('name');

FirebaseDatabaseListView(
  query: usersQuery,
  itemBuilder: (context, snapshot) {
    Map<String, dynamic> user = snapshot.value as Map<String, dynamic>;

    return Text('User name is ${user['name']}');
  },
);

The FirebaseDatabaseListView widget is built on-top of Flutter's own ListView widget, and accepts the same parameters which we can optionally provide. For example, to change the scroll-direction to horizontal:

FirebaseDatabaseListView(
  scrollDirection: Axis.horizontal,
  // ...
);

Controlling page size #

By default, the widget will fetch 10 items from the collection at a time. This can be changed by providing a pageSize parameter:

FirebaseDatabaseListView(
  pageSize: 20,
  // ...
);

In general, it is good practice to keep this value as small as possible to reduce network overhead. If the height (or width) of an individual item is large, it is recommended to lower the page size.

Loading and error handling #

By default, the widget will display a loading indicator while data is being fetched from the database, and ignore any errors which might be thrown (such as permission denied). You can override this behavior by providing a loadingBuilder and errorBuilder parameters to the widget:

FirebaseDatabaseListView(
  loadingBuilder: (context) => MyCustomLoadingIndicator(),
  errorBuilder: (context, error, stackTrace) => MyCustomError(error, stackTrace),
  // ...
);

Advanced configuration #

In many cases, the FirebaseDatabaseListView widget is enough to render simple lists of collection data. However, you may have specific requirements which require more control over the widget's behavior (such as using a GridView).

The FirebaseDatabaseQueryBuilder provides the building blocks for advanced configuration at the expense of requiring more boilerplate code. The widget does not provide any underlying list implementation, instead you are expected to provide this yourself.

Much like the FirebaseDatabaseListView widget, provide a query and builder:

final usersQuery = FirebaseDatabase.instance.ref('users').orderByChild('name');

FirebaseDatabaseQueryBuilder(
  query: usersQuery,
  builder: (context, snapshot, _) {
    // ... TODO!
  },
);

The main difference to note here is that the builder property returns a FirebaseQueryBuilderSnapshot, rather than an individual document. The builder returns the current state of the entire query, such as whether data is loading, an error has occurred and the documents.

This requires us to implement our own list based implementation. Firstly, let's handle the loading and error states:

FirebaseDatabaseQueryBuilder(
  query: usersQuery,
  builder: (context, snapshot, _) {
    if (snapshot.isFetching) {
      return const CircularProgressIndicator();
    }

    if (snapshot.hasError) {
      return Text('Something went wrong! ${snapshot.error}');
    }

    // ...
  },
);

Next, we now need to return a list-view based implementation for our application to display the data. For example, to display a grid of users, we can use the GridView widget:

FirebaseDatabaseQueryBuilder(
  query: usersQuery,
  builder: (context, snapshot, _) {
    // ...

    return GridView.builder(
      itemCount: snapshot.docs.length,
      itemBuilder: (context, index) {
        // if we reached the end of the currently obtained items, we try to
        // obtain more items
        if (snapshot.hasMore && index + 1 == snapshot.docs.length) {
          // Tell FirebaseDatabaseQueryBuilder to try to obtain more items.
          // It is safe to call this function from within the build method.
          snapshot.fetchMore();
        }

        final user = snapshot.docs[index].value as Map<String, dynamic>;

        return Container(
          padding: const EdgeInsets.all(8),
          color: Colors.teal[100],
          child: const Text("User name is ${user['name']}"),
        );
      },
    );
  },
);

With more power comes more responsibility:

1. Within the itemBuilder of our GridView, we have to manually ensure that we call the fetchMore() method on the snapshot when more data is required.
2. The FirebaseDatabaseQueryBuilder does not provide a list-view based handler, instead you must provide your own implementation.