8000 feat(flutter_bloc): support listener current state by zbarbuto · Pull Request #4405 · felangel/bloc · GitHub
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feat(flutter_bloc): support listener current state #4405

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feat(flutter_bloc): support listener current state #4405

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0937ca0
feat(flutter_bloc): support listener current state
zbarbuto Apr 11, 2025
d6c10c9
Merge branch 'master' into feature/current-state
zbarbuto Apr 16, 2025
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53 changes: 52 additions & 1 deletion packages/flutter_bloc/lib/src/bloc_listener.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -74,6 +74,31 @@ typedef BlocListenerCondition<S> = bool Function(S previous, S current);
/// )
/// ```
/// {@endtemplate}
///
/// {@template bloc_listener_start_with_current_state}
/// By default, the [listener] will only be called on new state emissions from
/// the bloc. If you want to call the listener with the current state
/// immediately, set [startWithCurrentState] to true.
/// Note that [listenWhen] is not called for the current state (as there is no
/// previous state to compare to).
///
/// ```dart
/// // Default behavior
/// BlocListener<BlocA, BlocAState>(
/// listener: (context, state) {
/// // this is only called when BlocA emits new states
/// },
/// )
///
/// BlocListener<BlocA, BlocAState>(
/// startWithCurrentState: true,
/// listener: (context, state) {
/// // this is now called immediately with BlocA's current state
/// // in addition to new emissions
/// },
/// )
/// ```
/// {@endtemplate}
class BlocListener<B extends StateStreamable<S>, S>
extends BlocListenerBase<B, S> {
/// {@macro bloc_listener}
Expand All @@ -83,13 +108,15 @@ class BlocListener<B extends StateStreamable<S>, S>
Key? key,
B? bloc,
BlocListenerCondition<S>? listenWhen,
bool startWithCurrentState = false,
Widget? child,
}) : super(
key: key,
child: child,
listener: listener,
bloc: bloc,
listenWhen: listenWhen,
startWithCurrentState: startWithCurrentState,
);
}

Expand All @@ -109,6 +136,7 @@ abstract class BlocListenerBase<B extends StateStreamable<S>, S>
this.bloc,
this.child,
this.listenWhen,
this.startWithCurrentState = false,
}) : super(key: key, child: child);

/// The widget which will be rendered as a descendant of the
Expand All @@ -127,6 +155,9 @@ abstract class BlocListenerBase<B extends StateStreamable<S>, S>
/// {@macro bloc_listener_listen_when}
final BlocListenerCondition<S>? listenWhen;

/// {@macro bloc_listener_start_with_current_state}
final bool startWithCurrentState;

@override
SingleChildState<BlocListenerBase<B, S>> createState() =>
_BlocListenerBaseState<B, S>();
Expand All @@ -142,6 +173,14 @@ abstract class BlocListenerBase<B extends StateStreamable<S>, S>
'listenWhen',
listenWhen,
),
)
..add(
FlagProperty(
'startWithCurrentState',
value: startWithCurrentState,
ifTrue: 'with current state',
ifFalse: 'without current state',
),
);
}
}
Expand Down Expand Up @@ -209,8 +248,20 @@ class _BlocListenerBaseState<B extends StateStreamable<S>, S>
super.dispose();
}

Stream<T> _startWithValue<T>(
T value,
Stream<T> originalStream,
) async* {
yield value;
yield* originalStream;
}

void _subscribe() {
_subscription = _bloc.stream.listen((state) {
final stream = widget.startWithCurrentState
? _startWithValue(_bloc.state, _bloc.stream)
: _bloc.stream;

_subscription = stream.listen((state) {
if (!mounted) return;
if (widget.listenWhen?.call(_previousState, state) ?? true) {
widget.listener(context, state);
Expand Down
47 changes: 47 additions & 0 deletions packages/flutter_bloc/test/bloc_listener_test.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -507,6 +507,52 @@ void main() {
expect(states, expectedStates);
});

testWidgets(
'calls listener with initial state when startWithCurrentState is true',
(tester) async {
final counterCubit = CounterCubit();
final states = <int>[];
const expectedStates = [0];
await tester.pumpWidget(
BlocListener<CounterCubit, int>(
bloc: counterCubit,
startWithCurrentState: true,
listener: (_, state) {
states.add(state);
},
child: const SizedBox(),
),
);

await tester.pump();

expect(states, expectedStates);
});

testWidgets(
'calls listener when further states emitted when startWithCurrentState '
'is true', (tester) async {
final counterCubit = CounterCubit();
final states = <int>[];
const expectedStates = [0, 1];
await tester.pumpWidget(
BlocListener<CounterCubit, int>(
bloc: counterCubit,
startWithCurrentState: true,
listener: (_, state) {
states.add(state);
},
child: const SizedBox(),
),
);

await tester.pump();
counterCubit.increment();
await tester.pump();

expect(states, expectedStates);
});

testWidgets('overrides debugFillProperties', (tester) async {
final builder = DiagnosticPropertiesBuilder();

Expand All @@ -528,6 +574,7 @@ void main() {
"bloc: Instance of 'CounterCubit'",
'has listener',
'has listenWhen',
'without current state',
],
);
});
Expand Down
0