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The window singleton is deprecated

Contents

Summary

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In preparation for supporting multiple views and multiple windows, the window singleton has been deprecated. Code previously relying on the window singleton needs to look up the specific view it wants to operate on via the View.of API or interact with the PlatformDispatcher directly.

Context

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Originally, Flutter assumed that an application would only consist of a single view (the window) into which content can be drawn. In a multi-view world, this assumption no longer makes sense and the APIs encoding this assumption have been deprecated. Instead, applications and libraries that relied on these APIs must choose a specific view they want to operate on and migrate to new multi-view compatible APIs as outlined in this migration guide.

Description of change

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The APIs that have been deprecated as part of this change are:

  • The global window property exposed by dart:ui.
  • The window property on the BaseBinding class, which is usually accessed via
    • GestureBinding.instance.window,
    • SchedulerBinding.instance.window,
    • ServicesBinding.instance.window,
    • PaintingBinding.instance.window,
    • SemanticsBinding.instance.window,
    • RendererBinding.instance.window,
    • WidgetsBinding.instance.window, or
    • WidgetTester.binding.window.
  • The SingletonFlutterView class from dart:ui.
  • TestWindow from flutter_test, its constructors, and all of its properties and methods.

The following options exist to migrate application and library code that relies on these deprecated APIs:

If a BuildContext is available, consider looking up the current FlutterView via View.of. This returns the FlutterView into which the widgets built by the build method associated with the given context will be drawn. The FlutterView provides access to the same functionality that was previously available on the deprecated SingletonFlutterView class returned by the deprecated window properties mentioned above. However, some of the platform-specific functionality has moved to the PlatformDispatcher, which can be accessed from the FlutterView returned by View.of via FlutterView.platformDispatcher. Using View.of is the preferred way of migrating away from the deprecated properties mentioned above.

If no BuildContext is available to look up a FlutterView, the PlatformDispatcher can be consulted directly to access platform-specific functionality. It also maintains a list of all available FlutterViews in PlatformDispatcher.views to access view-specific functionality. If possible, the PlatformDispatcher should be accessed via a binding (for example WidgetsBinding.instance.platformDispatcher) instead of using the static PlatformDispatcher.instance property. This ensures that the functionality of the PlatformDispatcher can be properly mocked out in tests.

Testing

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For tests that accessed the WidgetTester.binding.window property to change window properties for testing, the following migrations are available:

In tests written with testWidgets, two new properties have been added that together replace the functionality of TestWindow.

  • WidgetTester.view will provide a TestFlutterView that can be modified similarly to WidgetTester.binding.window, but with only view-specific properties such as the size of a view, its display pixel ratio, etc.
    • WidgetTester.viewOf is available for certain multi-view use cases, but should not be required for any migrations from WidgetTester.binding.window.
  • WidgetTester.platformDispatcher will provide access to a TestPlatformDispatcher that can be used to modify platform specific properties such as the platform's locale, whether certain system features are available, etc.

Migration guide

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Instead of accessing the static window property, application and library code that has access to a BuildContext should use View.of to look up the FlutterView the context is associated with. Some properties have moved to the PlatformDispatcher accessible from the view via the platformDispatcher getter.

Code before migration:

dart
Widget build(BuildContext context) {
  final double dpr = WidgetsBinding.instance.window.devicePixelRatio;
  final Locale locale = WidgetsBinding.instance.window.locale;
  return Text('The device pixel ratio is $dpr and the locale is $locale.');
}

Code after migration:

dart
Widget build(BuildContext context) {
  final double dpr = View.of(context).devicePixelRatio;
  final Locale locale = View.of(context).platformDispatcher.locale;
  return Text('The device pixel ratio is $dpr and the locale is $locale.');
}

If no BuildContext is available, the PlatformDispatcher exposed by the bindings can be consulted directly.

Code before migration:

dart
double getTextScaleFactor() {
  return WidgetsBinding.instance.window.textScaleFactor;
}

Code after migration:

dart
double getTextScaleFactor() {
  // View.of(context).platformDispatcher.textScaleFactor if a BuildContext is available, otherwise:
  return WidgetsBinding.instance.platformDispatcher.textScaleFactor;
}

Testing

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In tests written with testWidget, the new view and platformDispatcher accessors should be used instead.

Setting view-specific properties

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TestFlutterView has also made an effort to make the test API clearer and more concise by using setters with the same name as their related getter instead of setters with the TestValue suffix.

Code before migration:

dart
testWidget('test name', (WidgetTester tester) async {
  tester.binding.window.devicePixelRatioTestValue = 2.0;
  tester.binding.window.displayFeaturesTestValue = <DisplayFeatures>[];
  tester.binding.window.gestureSettingsTestValue = const GestureSettings(physicalTouchSlop: 100);
  tester.binding.window.paddingTestValue = FakeViewPadding.zero;
  tester.binding.window.physicalGeometryTestValue = const Rect.fromLTRB(0,0, 500, 800);
  tester.binding.window.physicalSizeTestValue = const Size(300, 400);
  tester.binding.window.systemGestureInsetsTestValue = FakeViewPadding.zero;
  tester.binding.window.viewInsetsTestValue = FakeViewPadding.zero;
  tester.binding.window.viewPaddingTestValue = FakeViewPadding.zero;
});

Code after migration

dart
testWidget('test name', (WidgetTester tester) async {
  tester.view.devicePixelRatio = 2.0;
  tester.view.displayFeatures = <DisplayFeatures>[];
  tester.view.gestureSettings = const GestureSettings(physicalTouchSlop: 100);
  tester.view.padding = FakeViewPadding.zero;
  tester.view.physicalGeometry = const Rect.fromLTRB(0,0, 500, 800);
  tester.view.physicalSize = const Size(300, 400);
  tester.view.systemGestureInsets = FakeViewPadding.zero;
  tester.view.viewInsets = FakeViewPadding.zero;
  tester.view.viewPadding = FakeViewPadding.zero;
});

Resetting view-specific properties

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TestFlutterView retains the capability to reset individual properties or the entire view but, in order to be more clear and consist, the naming of these methods has changed from clear<property>TestValue and clearAllTestValues to reset<property> and reset respectively.

Resetting individual properties
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Code before migration:

dart
testWidget('test name', (WidgetTester tester) async {
  addTearDown(tester.binding.window.clearDevicePixelRatioTestValue);
  addTearDown(tester.binding.window.clearDisplayFeaturesTestValue);
  addTearDown(tester.binding.window.clearGestureSettingsTestValue);
  addTearDown(tester.binding.window.clearPaddingTestValue);
  addTearDown(tester.binding.window.clearPhysicalGeometryTestValue);
  addTearDown(tester.binding.window.clearPhysicalSizeTestValue);
  addTearDown(tester.binding.window.clearSystemGestureInsetsTestValue);
  addTearDown(tester.binding.window.clearViewInsetsTestValue);
  addTearDown(tester.binding.window.clearViewPaddingTestValue);
});

Code after migration

dart
testWidget('test name', (WidgetTester tester) async {
  addTearDown(tester.view.resetDevicePixelRatio);
  addTearDown(tester.view.resetDisplayFeatures);
  addTearDown(tester.view.resetGestureSettings);
  addTearDown(tester.view.resetPadding);
  addTearDown(tester.view.resetPhysicalGeometry);
  addTearDown(tester.view.resetPhysicalSize);
  addTearDown(tester.view.resetSystemGestureInsets);
  addTearDown(tester.view.resetViewInsets);
  addTearDown(tester.view.resetViewPadding);
});
Resetting all properties at once
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Code before migration:

dart
testWidget('test name', (WidgetTester tester) async {
  addTearDown(tester.binding.window.clearAllTestValues);
});

Code after migration

dart
testWidget('test name', (WidgetTester tester) async {
  addTearDown(tester.view.reset);
});

Setting platform-specific properties

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TestPlatformDispatcher retains the same functionality and naming scheme for test setters as did TestWindow, so migration of platform-specific properties mainly consists of calling the same setters on the new WidgetTester.platformDispatcher accessor.

Code before migration:

dart
testWidgets('test name', (WidgetTester tester) async {
  tester.binding.window.accessibilityFeaturesTestValue = FakeAccessibilityFeatures.allOn;
  tester.binding.window.alwaysUse24HourFormatTestValue = false;
  tester.binding.window.brieflyShowPasswordTestValue = true;
  tester.binding.window.defaultRouteNameTestValue = '/test';
  tester.binding.window.initialLifecycleStateTestValue = 'painting';
  tester.binding.window.localesTestValue = <Locale>[const Locale('en-us'), const Locale('ar-jo')];
  tester.binding.window.localeTestValue = const Locale('ar-jo');
  tester.binding.window.nativeSpellCheckServiceDefinedTestValue = false;
  tester.binding.window.platformBrightnessTestValue = Brightness.dark;
  tester.binding.window.semanticsEnabledTestValue = true;
  tester.binding.window.textScaleFactorTestValue = 2.0;
});

Code after migration:

dart
testWidgets('test name', (WidgetTester tester) async {
  tester.platformDispatcher.accessibilityFeaturesTestValue = FakeAccessibilityFeatures.allOn;
  tester.platformDispatcher.alwaysUse24HourFormatTestValue = false;
  tester.platformDispatcher.brieflyShowPasswordTestValue = true;
  tester.platformDispatcher.defaultRouteNameTestValue = '/test';
  tester.platformDispatcher.initialLifecycleStateTestValue = 'painting';
  tester.platformDispatcher.localesTestValue = <Locale>[const Locale('en-us'), const Locale('ar-jo')];
  tester.platformDispatcher.localeTestValue = const Locale('ar-jo');
  tester.platformDispatcher.nativeSpellCheckServiceDefinedTestValue = false;
  tester.platformDispatcher.platformBrightnessTestValue = Brightness.dark;
  tester.platformDispatcher.semanticsEnabledTestValue = true;
  tester.platformDispatcher.textScaleFactorTestValue = 2.0;
});

Resetting platform-specific properties

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Similarly to setting properties, resetting platform-specific properties consists mainly of changing from the binding.window accessor to the platformDispatcher accessor.

Resetting individual properties
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Code before migration:

dart
testWidgets('test name', (WidgetTester tester) async {
  addTeardown(tester.binding.window.clearAccessibilityFeaturesTestValue);
  addTeardown(tester.binding.window.clearAlwaysUse24HourFormatTestValue);
  addTeardown(tester.binding.window.clearBrieflyShowPasswordTestValue);
  addTeardown(tester.binding.window.clearDefaultRouteNameTestValue);
  addTeardown(tester.binding.window.clearInitialLifecycleStateTestValue);
  addTeardown(tester.binding.window.clearLocalesTestValue);
  addTeardown(tester.binding.window.clearLocaleTestValue);
  addTeardown(tester.binding.window.clearNativeSpellCheckServiceDefinedTestValue);
  addTeardown(tester.binding.window.clearPlatformBrightnessTestValue);
  addTeardown(tester.binding.window.clearSemanticsEnabledTestValue);
  addTeardown(tester.binding.window.clearTextScaleFactorTestValue);
});

Code after migration:

dart
testWidgets('test name', (WidgetTester tester) async {
  addTeardown(tester.platformDispatcher.clearAccessibilityFeaturesTestValue);
  addTeardown(tester.platformDispatcher.clearAlwaysUse24HourFormatTestValue);
  addTeardown(tester.platformDispatcher.clearBrieflyShowPasswordTestValue);
  addTeardown(tester.platformDispatcher.clearDefaultRouteNameTestValue);
  addTeardown(tester.platformDispatcher.clearInitialLifecycleStateTestValue);
  addTeardown(tester.platformDispatcher.clearLocalesTestValue);
  addTeardown(tester.platformDispatcher.clearLocaleTestValue);
  addTeardown(tester.platformDispatcher.clearNativeSpellCheckServiceDefinedTestValue);
  addTeardown(tester.platformDispatcher.clearPlatformBrightnessTestValue);
  addTeardown(tester.platformDispatcher.clearSemanticsEnabledTestValue);
  addTeardown(tester.platformDispatcher.clearTextScaleFactorTestValue);
});
Resetting all properties at once
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Code before migration:

dart
testWidgets('test name', (WidgetTester tester) async {
  addTeardown(tester.binding.window.clearAllTestValues);
});

Code after migration:

dart
testWidgets('test name', (WidgetTester tester) async {
  addTeardown(tester.platformDispatcher.clearAllTestValues);
});

Timeline

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Landed in version: 3.9.0-13.0.pre.20
In stable release: 3.10.0

References

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API documentation:

Relevant issues:

Relevant PRs:

Unless stated otherwise, the documentation on this site reflects the latest stable version of Flutter. Page last updated on 2024-04-04. View source or report an issue.