StreamBuilder<T> class
Component that builds itself based on the latest snapshot of interaction with a Stream.
Component rebuilding is scheduled by each interaction, using State.setState, but is otherwise decoupled from the timing of the stream. The builder is called at the discretion of the Flutter pipeline, and will thus receive a timing-dependent sub-sequence of the snapshots that represent the interaction with the stream.
As an example, when interacting with a stream producing the integers 0 through 9, the builder may be called with any ordered sub-sequence of the following snapshots that includes the last one (the one with ConnectionState.done):
AsyncSnapshot<int>.withData(ConnectionState.waiting, null)
AsyncSnapshot<int>.withData(ConnectionState.active, 0)
AsyncSnapshot<int>.withData(ConnectionState.active, 1)
- ...
AsyncSnapshot<int>.withData(ConnectionState.active, 9)
AsyncSnapshot<int>.withData(ConnectionState.done, 9)
The actual sequence of invocations of the builder depends on the relative timing of events produced by the stream and the build rate of the Flutter pipeline.
Changing the StreamBuilder configuration to another stream during event generation introduces snapshot pairs of the form:
AsyncSnapshot<int>.withData(ConnectionState.none, 5)
AsyncSnapshot<int>.withData(ConnectionState.waiting, 5)
The latter will be produced only when the new stream is non-null, and the former only when the old stream is non-null.
The stream may produce errors, resulting in snapshots of the form:
AsyncSnapshot<int>.withError(ConnectionState.active, 'some error', someStackTrace)
The data and error fields of snapshots produced are only changed when the
state is ConnectionState.active
.
The initial snapshot data can be controlled by specifying initialData. 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 dartpad} This sample shows a StreamBuilder that listens to a Stream that emits bids for an auction. Every time the StreamBuilder receives a bid from the Stream, it will display the price of the bid below an icon. If the Stream emits an error, the error is displayed below an error icon. When the Stream finishes emitting bids, the final price is displayed.
** See code in examples/api/lib/components/async/stream_builder.0.dart ** {@end-tool}
See also:
ValueListenableBuilder
, which wraps a ValueListenable instead of a Stream.- StreamBuilderBase, which supports component building based on a computation that spans all interactions made with the stream.
- Inheritance
-
- Object
- Component
- StatefulComponent
- StreamBuilderBase<
T, AsyncSnapshot< T> > - StreamBuilder
Constructors
-
StreamBuilder({Key? key, T? initialData, Stream<
T> ? stream, required AsyncComponentBuilder<T> builder}) -
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.
const
Properties
-
builder
→ AsyncComponentBuilder<
T> -
The build strategy currently used by this builder.
final
- hashCode → int
-
The hash code for this object.
no setterinherited
- initialData → T?
-
The data that will be used to create the initial snapshot.
final
- key → Key?
-
Controls how one component replaces another component in the tree.
finalinherited
- runtimeType → Type
-
A representation of the runtime type of the object.
no setterinherited
-
stream
→ Stream<
T> ? -
The asynchronous computation to which this builder is currently connected,
possibly null. When changed, the current summary is updated using
afterDisconnected, if the previous stream was not null, followed by
afterConnected, if the new stream is not null.
finalinherited
Methods
-
afterConnected(
AsyncSnapshot< T> current) → AsyncSnapshot<T> -
Returns an updated version of the
current
summary reflecting that we are now connected to a stream.override -
afterData(
AsyncSnapshot< T> current, T data) → AsyncSnapshot<T> -
Returns an updated version of the
current
summary following a data event.override -
afterDisconnected(
AsyncSnapshot< T> current) → AsyncSnapshot<T> -
Returns an updated version of the
current
summary reflecting that we are no longer connected to a stream.override -
afterDone(
AsyncSnapshot< T> current) → AsyncSnapshot<T> -
Returns an updated version of the
current
summary following stream termination.override -
afterError(
AsyncSnapshot< T> current, Object error, StackTrace stackTrace) → AsyncSnapshot<T> -
Returns an updated version of the
current
summary following an error with a stack trace.override -
build(
BuildContext context, AsyncSnapshot< T> currentSummary) → Iterable<Component> -
Returns a Component based on the
currentSummary
.override -
createElement(
) → Element -
Creates a StatefulElement to manage this component's location in the tree.
inherited
-
createState(
) → State< StreamBuilderBase< T, AsyncSnapshot< >T> > -
Creates the mutable state for this component at a given location in the tree.
inherited
-
initial(
) → AsyncSnapshot< T> -
Returns the initial summary of stream interaction, typically representing
the fact that no interaction has happened at all.
override
-
noSuchMethod(
Invocation invocation) → dynamic -
Invoked when a nonexistent method or property is accessed.
inherited
-
toString(
) → String -
A string representation of this object.
inherited
Operators
-
operator ==(
Object other) → bool -
The equality operator.
inherited