Skip to main content

A month of Flutter: rendering a ListView with StreamBuilder

Originally published on
The data for Birb will be stored in Firebase Cloud Firestore. When looking at patterns to handle getting and rendering data, I decided to go with the StreamBuilder example from the cloud_firestore package documentation. I don't know how well pagination will work with this approach so that will be an experiment for another day.
The first change I'm making is turning the static List<int> into a Stream, and moving it further up the widget tree. I want the PostsList widget to only care about rendering items from a Stream, not how to create the Streamitself. This has the bonus of making it easier to mock data in the tests.
final Stream<List<int>> _posts = Stream<List<int>>.fromIterable(
    List<int>.generate(10, (int i) => i),
This looks a little weird but it is basically generating a list of 10 items. That List of 10 items is used as the first value in a new Stream. From the subscription side of the Stream, there will be a single event with data that is a List of 10 items. I'm going with this pattern because Firestore will have snapshots with multiple documents.
The PostsList build method needs to be updated to consume the Stream and use a StreamBuilder:
Widget build(BuildContext context) {
  return StreamBuilder<List<int>>(
    stream: posts,
    builder: (BuildContext context, AsyncSnapshot<List<int>> snapshot) {
      if (snapshot.hasError) {
        return Text('Error: ${snapshot.error}');
       switch (snapshot.connectionState) {
        case ConnectionState.waiting:
          return const Text('Loading...');
          if ( {
            return const NoContent();
          return _itemList(;
The StreamBuilder takes a Stream and will then call the builder with an AsyncSnapshot. There are a couple of different states on this snapshot that need to be handled:
  • The first is checking to see if there has been an error. If there has been, render some error text.
  • Second, if the connection is waiting, show a loader while waiting for data to arrive.
  • Third, if there is no data, render the NoContent widget.
  • Finally if none of the previous cases are met, render the actual data.
Looking at the tests for PostList, all four of those scenarios are tested by creating different kinds of mock streams with the _postsStream helper.
Stream<List<int>> _postsStream(int count) {
  return Stream<List<int>>.fromIterable(
      List<int>.generate(count, (int i) => i),
Then I can test that the loading text is shown, followed a test that all the mocked items are rendered.
testWidgets('renders list of PostItems', (WidgetTester tester) async {
  // Build our app and trigger a frame.
  await tester.pumpWidget(MaterialApp(
    home: PostsList(_postsStream(5)),

  expect(find.text('Loading...'), findsOneWidget);

  await tester.pump(;

  expect(find.byType(PostItem), findsNWidgets(5));
To simulate the error case, I can throw an error on a Future and convert that to a stream.
testWidgets('renders NoContent widget', (WidgetTester tester) async {
  // Build our app and trigger a frame.
  await tester.pumpWidget(MaterialApp(
    home: PostsList(Future<List<int>>.error('Bad Connection').asStream()),

  await tester.pump(;
   expect(find.text('Error: Bad Connection'), findsOneWidget);
One other minor change I made was to reduce the height of the cards so I could be sure the additional cards were rendering.

Code changes


Popular posts from this blog

Installing Storytlr the lifestreaming platform

" Storytlr  is an open source lifestreaming and micro blogging platform. You can use it for a single user or it can act as a host for many people all from the same installation." I've been looking for something like Storytlr for a few months now or at least trying to do it with Drupal . While I love Drupal and FeedAPI  I did not want to spend all that time building a lifestream website. So I've been playing around with Storytlr instead and found it very easy. Here is how I got it up and running on a Ubuntu EC2 server. You can also check out the official Storytlr install instructions . Assumptions: LAMP stack installed and running. Domain setup for a directory. MySQL database and user ready to go. Lets get started! Get the code : wget tar -xvzf storytlr-0.9.2.tgz You can find out the  latest stable release  on Storytlr's downloads page. Import the database : Within protected/install is database.sq

Google+ could bring world peace

Google is the largest web application on the planet with over one billion unique visiters each month. This means that one in seven people on the entire planet used Google over the last 30 days. Having such a massive user base means that someone from pretty much every single geographical, political, and religious group is a user of Google. Once Google+  hits a billion our pals from Mountain View will be in the unique position of potentially bringing about world peace. And I don't mean bringing FarmVille to Google+. How so, you might ask? Well Google is collecting so much personal information that they can create incredibly accurate profiles of personal beliefs and comfort zones. With these personas, the 900,000 machines , a few algorithms, and some time Google can connect people one follow at a time that are of similar interests but ever so slightly contrarian. Eventually even the most conservative views will become more open and accepting just through the everyday contact. On

Sync is currently experiencing problems

Update : I now recommend you install Google Chrome  and  disable  the built in Browser as it supports encrypting all synced data. After picking up a gorgeous  Galaxy Nexus yesterday I was running into an issue where my browser data wasn't syncing to the phone. After a little Googling I found this is commonly caused by having all of my synced Chrome data encrypted instead of the default of only encrypting the passwords. These are the steps I went through to get my dat syncing again without losing any of it. The exact error I was getting was "Sync is currently experiencing problems. It will be back shortly." In Google Chrome open the personal stuff settings page by clicking this link or by opening the wrench menu, and click on "signed in with".  Hit "disconnect your Google Account" to temporarily disable syncing from your browser. Visit the Google Dashboard and "Stop sync and delete data from Google". I waite