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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>