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Improve StreamBuilder documentation (#23713)

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Ian Hickson 2018-11-26 12:17:57 -08:00 committed by GitHub
parent 06e4ccc9a9
commit aae968cd45
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1 changed files with 33 additions and 22 deletions
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55
packages/flutter/lib/src/widgets/async.dart
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@ -36,14 +36,14 @@ import 'framework.dart';
/// termination by overriding [afterDone]. Finally, the summary may be updated
/// on change of stream by overriding [afterDisconnected] and [afterConnected].
///
/// [T] is the type of stream events.
/// `T` is the type of stream events.
///
/// [S] is the type of interaction summary.
/// `S` is the type of interaction summary.
///
/// See also:
///
/// * [StreamBuilder], which is specialized to the case where only the most
/// recent interaction is needed for widget building.
/// * [StreamBuilder], which is specialized for the case where only the most
/// recent interaction is needed for widget building.
abstract class StreamBuilderBase<T, S> extends StatefulWidget {
/// Creates a [StreamBuilderBase] connected to the specified [stream].
const StreamBuilderBase({ Key key, this.stream }) : super(key: key);
@ -286,9 +286,9 @@ class AsyncSnapshot<T> {
/// See also:
///
/// * [StreamBuilder], which delegates to an [AsyncWidgetBuilder] to build
/// itself based on a snapshot from interacting with a [Stream].
/// itself based on a snapshot from interacting with a [Stream].
/// * [FutureBuilder], which delegates to an [AsyncWidgetBuilder] to build
/// itself based on a snapshot from interacting with a [Future].
/// itself based on a snapshot from interacting with a [Future].
typedef AsyncWidgetBuilder<T> = Widget Function(BuildContext context, AsyncSnapshot<T> snapshot);
/// Widget that builds itself based on the latest snapshot of interaction with
@ -333,14 +333,9 @@ typedef AsyncWidgetBuilder<T> = Widget Function(BuildContext context, AsyncSnaps
/// state is `ConnectionState.active`.
///
/// The initial snapshot data can be controlled by specifying [initialData].
/// You would use this facility to ensure that if the [builder] is invoked
/// before the first event arrives on the stream, the snapshot carries data of
/// your choice rather than the default null value.
///
/// See also:
///
/// * [StreamBuilderBase], which supports widget building based on a computation
/// that spans all interactions made with the stream.
/// This should be used to ensure that the first frame has the expected value,
/// as the builder will always be called before the stream listener has a chance
/// to be processed.
///
/// {@tool sample}
///
@ -365,25 +360,41 @@ typedef AsyncWidgetBuilder<T> = Widget Function(BuildContext context, AsyncSnaps
/// )
/// ```
/// {@end-tool}
// TODO(ianh): remove unreachable code above once https://github.com/dart-lang/linter/issues/1141 is fixed
///
/// See also:
///
/// * [ValueListenableBuilder], which wraps a [ValueListenable] instead of a
/// [Stream].
/// * [StreamBuilderBase], which supports widget building based on a computation
/// that spans all interactions made with the stream.
// TODO(ianh): remove unreachable code above once https://github.com/dart-lang/linter/issues/1139 is fixed
class StreamBuilder<T> extends StreamBuilderBase<T, AsyncSnapshot<T>> {
/// Creates a new [StreamBuilder] that builds itself based on the latest
/// snapshot of interaction with the specified [stream] and whose build
/// strategy is given by [builder]. The [initialData] is used to create the
/// initial snapshot. It is null by default.
/// strategy is given by [builder].
///
/// The [initialData] is used to create the initial snapshot.
///
/// The [builder] must not be null.
const StreamBuilder({
Key key,
this.initialData,
Stream<T> stream,
@required this.builder
})
: assert(builder != null),
super(key: key, stream: stream);
}) : assert(builder != null),
super(key: key, stream: stream);
/// The build strategy currently used by this builder. Cannot be null.
/// The build strategy currently used by this builder.
final AsyncWidgetBuilder<T> builder;
/// The data that will be used to create the initial snapshot. Null by default.
/// The data that will be used to create the initial snapshot.
///
/// Providing this value (presumably obtained sychronously somehow when the
/// [Stream] was created) ensures that the first frame will show useful data.
/// Otherwise, the first frame will be built with the value null, regardless
/// of whether a value is available on the stream: since streams are
/// asynchronous, no events from the stream can be obtained before the initial
/// build.
final T initialData;
@override