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A pragmatic StreamBuilder with sensible defaults

DataStreamBuilder #


A pragmatic StreamBuilder with sensible defaults.

😩 The problem with StreamBuilder #

StreamBuilder is an essential tool to work with BLoCs or generally any stream.

But with enough streams in our codebase, a lot of boilerplate is introduced. Code gets repetitive and can't be easily reused:

  stream: bloc.stock,
  builder: (context, AsyncSnapshot<Stock> snapshot) {
    if (snapshot.hasData) {
      return Text(snapshot.data.stock.toString());
    } else if (snapshot.hasError) {
      return Text(snapshot.error.toString());
    return Center(child: CircularProgressIndicator());

DataStreamBuilder aims to fix these issues for the common usecase:

  stream: bloc.stock,
  builder: (context, Stock stock) => Text(stock.local.toString())

This library provides default builders for the loading and error states (can be supplied as loadingBuilder and errorBuilder), and only calls builder when data is present.

Depending on your current StreamBuilders this could be a drop-in replacement. In any case, it's super easy to migrate to DataStreamBuilder.

Note: if you need fine-grained control over ConnectionStates to the underlying computation, just use StreamBuilder.

👩🏾‍💻 Usage #

Using defaults for loading and error states:

  stream: Repository.of<Post>().findAll(),
  builder: (context, List<Post> posts) => ListView(
    children: posts.map((post) => ListTile(title: Text(post.body))).toList(),

In case you are wondering, these are the defaults:

Default loading widget:

(context) => Center(child: CircularProgressIndicator());

Default error widget:

(context, dynamic error) {
  error = error is Exception ? error.toString() : 'Error: $error';
  return Center(child: Text(
      textDirection: TextDirection.ltr,
      style: TextStyle(backgroundColor: Colors.red, color: Colors.white),

Another example with custom loading and error widgets:

  stream: Repository.of<Post>().findAll(),
  loadingBuilder: (context) => Center(child: Text('Loading posts...')),
  errorBuilder: (context, error) => PostErrorView(error),
  builder: (context, List<Post> posts) => ListView(
    children: posts.map((post) => ListTile(title: Text(post.body))).toList(),

Initial values can also be supplied:

// a stream that is a RxDart ValueObservable
final stream = Repository.of<Post>().findAll();

  stream: stream, // async access to stream
  initialData: stream.value, // sync access to latest value
  builder: (context, List<Post> posts) => ListView(
    children: posts.map((post) => ListTile(title: Text(post.body))).toList(),

See tests and the Example tab for a full example.

🛠 Extending #

We can easily extend the class in order to provide our own app-wide defaults.

For instance, we could implement a branded loader:

class BrandedDataStreamBuilder<T> extends DataStreamBuilder<T> {

  static final brandedLoadingBuilder = (context) => Text('Custom branded loading...');

    Key key,
    @required Stream<T> stream,
    @required DataWidgetBuilder<T> builder,
    DataErrorWidgetBuilder errorBuilder
  }) :
    assert(builder != null),
      key: key,
      stream: stream,
      builder: builder,
      loadingBuilder: brandedLoadingBuilder,
      errorBuilder: errorBuilder

In action:


➕ Collaborating #

Please use Github to open issues and send PRs. Thanks 🙌

📝 License #