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StreamBuilder |
widgets are used to display the results of a Future in the UI. |
The following example uses a FutureBuilder: |
<code_start>class HomePage extends StatelessWidget { |
const HomePage({super.key}); |
final HomePageViewModel viewModel = const HomePageViewModel(); |
@override |
Widget build(BuildContext context) { |
return CupertinoPageScaffold( |
// Feed a FutureBuilder to your widget tree. |
child: FutureBuilder<Weather>( |
// Specify the Future that you want to track. |
future: viewModel.load(), |
builder: (context, snapshot) { |
// A snapshot is of type `AsyncSnapshot` and contains the |
// state of the Future. By looking if the snapshot contains |
// an error or if the data is null, you can decide what to |
// show to the user. |
if (snapshot.hasData) { |
return Center( |
child: Text( |
snapshot.data.toString(), |
), |
); |
} else { |
return const Center( |
child: CupertinoActivityIndicator(), |
); |
} |
}, |
), |
); |
} |
}<code_end> |
For the complete example, check out the |
async_weather file on GitHub.<topic_end> |
<topic_start> |
Leveraging a background thread/isolate |
Flutter apps can run on a variety of multi-core hardware, |
including devices running macOS and iOS. |
To improve the performance of these applications, |
you must sometimes run tasks on different cores |
concurrently. This is especially important |
to avoid blocking UI rendering with long-running operations.In Swift, you can leverage GCD to run tasks on global queues |
with different quality of service class (qos) properties. |
This indicates the task’s priority.In Dart, you can offload computation to a worker isolate, |
often called a background worker. |
A common scenario spawns a simple worker isolate and |
returns the results in a message when the worker exits. |
As of Dart 2.19, you can use Isolate.run() to |
spawn an isolate and run computations:In Flutter, you can also use the compute function |
to spin up an isolate to run a callback function:In this case, the callback function is a top-level |
function as shown below:You can find more information on Dart at |
Learning Dart as a Swift developer, |
and more information on Flutter at |
Flutter for SwiftUI developers or |
Flutter for UIKit developers. |
<topic_end> |
<topic_start>Upgrading Flutter |
No matter which one of the Flutter release channels |
you follow, you can use the flutter command to upgrade your |
Flutter SDK or the packages that your app depends on.<topic_end> |
<topic_start> |
Upgrading the Flutter SDK |
To update the Flutter SDK use the flutter upgrade command:This command gets the most recent version of the Flutter SDK |
that’s available on your current Flutter channel.If you are using the stable channel |
and want an even more recent version of the Flutter SDK, |
switch to the beta channel using flutter channel beta, |
and then run flutter upgrade.<topic_end> |
<topic_start> |
Keeping informed |
We publish migration guides for known breaking changes.We send announcements regarding these changes to the |
Flutter announcements mailing list.To avoid being broken by future versions of Flutter, |
consider submitting your tests to our test registry.<topic_end> |
<topic_start> |
Switching Flutter channels |
Flutter has two release channels: |
stable and beta.<topic_end> |
<topic_start> |
The stable channel |
We recommend the stable channel for new users |
and for production app releases. |
The team updates this channel about every three months. |
The channel might receive occasional hot fixes |
for high-severity or high-impact issues.The continuous integration for the Flutter team’s plugins and packages |
includes testing against the latest stable release.The latest documentation for the stable branch |
is at: https://api.flutter.dev<topic_end> |
<topic_start> |
The beta channel |
The beta channel has the latest stable release. |
This is the most recent version of Flutter that we have heavily tested. |
This channel has passed all our public testing, |
has been verified against test suites for Google products that use Flutter, |
and has been vetted against contributed private test suites. |
The beta channel receives regular hot fixes |
to address newly discovered important issues.The beta channel is essentially the same as the stable channel |
but updated monthly instead of quarterly. |
Indeed, when the stable channel is updated, |
it is updated to the latest beta release.<topic_end> |
<topic_start> |
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