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(in the form of static fields, for example).The following example shows, in a simple isolate, how to share data back to
the main thread to update the UI.
<code_start>Future<void> loadData() async {
ReceivePort receivePort = ReceivePort();
await Isolate.spawn(dataLoader, receivePort.sendPort);
// The 'echo' isolate sends its SendPort as the first message.
SendPort sendPort = await receivePort.first;
List msg = await sendReceive(
sendPort,
'https://jsonplaceholder.typicode.com/posts',
);
setState(() {
widgets = msg;
});
}
// The entry point for the isolate.
static Future<void> dataLoader(SendPort sendPort) async {
// Open the ReceivePort for incoming messages.
ReceivePort port = ReceivePort();
// Notify any other isolates what port this isolate listens to.
sendPort.send(port.sendPort);
await for (var msg in port) {
String data = msg[0];
SendPort replyTo = msg[1];
String dataURL = data;
http.Response response = await http.get(Uri.parse(dataURL));
// Lots of JSON to parse
replyTo.send(jsonDecode(response.body));
}
}
Future sendReceive(SendPort port, msg) {
ReceivePort response = ReceivePort();
port.send([msg, response.sendPort]);
return response.first;
}<code_end>
Here, dataLoader() is the Isolate that runs in its own separate
execution thread. In the isolate you can perform more CPU intensive
processing (parsing a big JSON, for example),
or perform computationally intensive math,
such as encryption or signal processing.You can run the full example below:
<code_start>import 'dart:async';
import 'dart:convert';
import 'dart:isolate';
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
void main() {
runApp(const SampleApp());
}
class SampleApp extends StatelessWidget {
const SampleApp({super.key});
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Sample App',
theme: ThemeData(
colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
),
home: const SampleAppPage(),
);
}
}
class SampleAppPage extends StatefulWidget {
const SampleAppPage({super.key});
@override
State<SampleAppPage> createState() => _SampleAppPageState();
}
class _SampleAppPageState extends State<SampleAppPage> {
List widgets = [];
@override
void initState() {
super.initState();
loadData();
}
Widget getBody() {
bool showLoadingDialog = widgets.isEmpty;
if (showLoadingDialog) {
return getProgressDialog();
} else {
return getListView();
}
}
Widget getProgressDialog() {
return const Center(child: CircularProgressIndicator());
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: const Text('Sample App'),
),
body: getBody(),
);
}
ListView getListView() {
return ListView.builder(
itemCount: widgets.length,
itemBuilder: (context, position) {
return getRow(position);
},
);