text stringlengths 1 474 |
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animation.When using fling(), a Force is used to create a specific |
simulation which is then used to drive the controller.When using animateWith(), the given simulation is used to drive the |
controller.These methods all return the future that the Ticker provides and |
which will resolve when the controller next stops or changes |
simulation.<topic_end> |
<topic_start>Attaching animatables to animations |
Passing an Animation<double> (the new parent) to an Animatable’s |
animate() method creates a new Animation subclass that acts like |
the Animatable but is driven from the given parent. |
<topic_end> |
<topic_start>Accessibility |
Ensuring apps are accessible to a broad range of users is an essential |
part of building a high-quality app. Applications that are poorly |
designed create barriers to people of all ages. The UN Convention on |
the Rights of Persons with Disabilities states the moral and legal |
imperative to ensure universal access to information systems; countries |
around the world enforce accessibility as a requirement; and companies |
recognize the business advantages of maximizing access to their services.We strongly encourage you to include an accessibility checklist |
as a key criteria before shipping your app. Flutter is committed to |
supporting developers in making their apps more accessible, and includes |
first-class framework support for accessibility in addition to that |
provided by the underlying operating system, including:Details of these features are discussed below.<topic_end> |
<topic_start> |
Inspecting accessibility support |
In addition to testing for these specific topics, |
we recommend using automated accessibility scanners:<topic_end> |
<topic_start> |
Large fonts |
Both Android and iOS contain system settings to configure the desired font |
sizes used by apps. Flutter text widgets respect this OS setting when |
determining font sizes.Font sizes are calculated automatically by Flutter based on the OS setting. |
However, as a developer you should make sure your layout has enough room to |
render all its contents when the font sizes are increased. |
For example, you can test all parts of your app on a small-screen |
device configured to use the largest font setting.<topic_end> |
<topic_start> |
Example |
The following two screenshots show the standard Flutter app |
template rendered with the default iOS font setting, |
and with the largest font setting selected in iOS accessibility settings.<topic_end> |
<topic_start> |
Screen readers |
For mobile, screen readers (TalkBack, VoiceOver) |
enable visually impaired users to get spoken feedback about |
the contents of the screen and interact with the UI by using |
gestures on mobile and keyboard shortcuts on desktop. |
Turn on VoiceOver or TalkBack on your mobile device and |
navigate around your app.To turn on the screen reader on your device, complete the following steps:To learn how to find and customize Android’s |
accessibility features, view the following video.To learn how to find and customize iOS |
accessibility features, view the following video.For web, the following screen readers are currently supported:Mobile browsers:Desktop browsers:Screen readers users on web must toggle the |
“Enable accessibility” button to build the semantics tree. |
Users can skip this step if you programmatically auto-enable |
accessibility for your app using this API:Windows comes with a screen reader called Narrator |
but some developers recommend using the more popular |
NVDA screen reader. To learn about using NVDA to test |
Windows apps, check out |
Screen Readers 101 For Front-End Developers (Windows).On a Mac, you can use the desktop version of VoiceOver, |
which is included in macOS.On Linux, a popular screen reader is called Orca. |
It comes pre-installed with some distributions |
and is available on package repositories such as apt. |
To learn about using Orca, check out |
Getting started with Orca screen reader on Gnome desktop.Check out the following video demo to see Victor Tsaran, |
using VoiceOver with the now-archived Flutter Gallery web app.Flutter’s standard widgets generate an accessibility tree automatically. |
However, if your app needs something different, |
it can be customized using the Semantics widget.When there is text in your app that should be voiced |
with a specific voice, inform the screen reader |
which voice to use by calling TextSpan.locale. |
Note that MaterialApp.locale and Localizations.override |
don’t affect which voice the screen reader uses. |
Usually, the screen reader uses the system voice |
except where you explicitly set it with TextSpan.locale.<topic_end> |
<topic_start> |
Sufficient contrast |
Sufficient color contrast makes text and images easier to read. |
Along with benefitting users with various visual impairments, |
sufficient color contrast helps all users when viewing an interface |
on devices in extreme lighting conditions, |
such as when exposed to direct sunlight or on a display with low |
brightness.The W3C recommends:<topic_end> |
<topic_start> |
Building with accessibility in mind |
Ensuring your app can be used by everyone means building accessibility |
into it from the start. For some apps, that’s easier said than done. |
In the video below, two of our engineers take a mobile app from a dire |
accessibility state to one that takes advantage of Flutter’s built-in |
widgets to offer a dramatically more accessible experience.<topic_end> |
<topic_start> |
Testing accessibility on mobile |
Test your app using Flutter’s Accessibility Guideline API. |
This API checks if your app’s UI meets Flutter’s accessibility recommendations. |
These cover recommendations for text contrast, target size, and target labels.The following example shows how to use the Guideline API on Name Generator. |
You created this app as part of the |
Write your first Flutter app codelab. |
Each button on the app’s main screen serves as a tappable target |
with text represented in 18 point. |
<code_start>final SemanticsHandle handle = tester.ensureSemantics(); |
await tester.pumpWidget(MyApp()); |
// Checks that tappable nodes have a minimum size of 48 by 48 pixels |
// for Android. |
await expectLater(tester, meetsGuideline(androidTapTargetGuideline)); |
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