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Add assertion that snackbars have a place to go #103006

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merged 1 commit into from
May 4, 2022
Merged

Add assertion that snackbars have a place to go #103006

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5 changes: 5 additions & 0 deletions packages/flutter/lib/src/material/scaffold.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -265,6 +265,11 @@ class ScaffoldMessengerState extends State<ScaffoldMessenger> with TickerProvide
/// ** See code in examples/api/lib/material/scaffold/scaffold_messenger_state.show_snack_bar.0.dart **
/// {@end-tool}
ScaffoldFeatureController<SnackBar, SnackBarClosedReason> showSnackBar(SnackBar snackBar) {
assert(
_scaffolds.isNotEmpty,
'ScaffoldMessenger.showSnackBar was called, but there are currently no '
'descendant Scaffolds to present to.',
);
_snackBarController ??= SnackBar.createAnimationController(vsync: this)
..addStatusListener(_handleSnackBarStatusChanged);
if (_snackBars.isEmpty) {
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28 changes: 28 additions & 0 deletions packages/flutter/test/material/snack_bar_test.dart
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Expand Up @@ -2090,6 +2090,34 @@ void main() {
await tester.pump(const Duration(milliseconds: 750));
await expectLater(find.byType(MaterialApp), matchesGoldenFile('snack_bar.goldenTest.backdropFilter.png'));
});

testWidgets('ScaffoldMessenger will alert for snackbars that cannot be presented', (WidgetTester tester) async {
// Regression test for https://github.com/flutter/flutter/issues/103004
await tester.pumpWidget(const MaterialApp(
home: Center(),
));

final ScaffoldMessengerState scaffoldMessengerState = tester.state<ScaffoldMessengerState>(
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I've never seen tester.state before!

find.byType(ScaffoldMessenger),
);
expect(
() {
scaffoldMessengerState.showSnackBar(const SnackBar(
content: Text('I am a snack bar.'),
));
},
throwsA(
isA<AssertionError>().having(
(AssertionError error) => error.toString(),
'description',
contains(
'ScaffoldMessenger.showSnackBar was called, but there are currently '
'no descendant Scaffolds to present to.'
)
),
),
);
});
}

/// Start test for "SnackBar dismiss test".
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