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});
}
// the entry point for the isolate
static future<void> dataLoader(SendPort sendPort) async {
// open the ReceivePort for incoming messages.
final ReceivePort port = ReceivePort();
// notify any other isolates what port this isolate listens to.
sendPort.send(port.sendPort);
await for (final dynamic msg in port) {
final string url = msg[0] as string;
final SendPort replyTo = msg[1] as SendPort;
final uri dataURL = uri.parse(url);
final http.Response response = await http.get(dataURL);
// lots of JSON to parse
replyTo.send(jsonDecode(response.body) as List<Map<String, dynamic>>);
}
}
Future<List<Map<String, dynamic>>> sendReceive(SendPort port, string msg) {
final ReceivePort response = ReceivePort();
port.send(<dynamic>[msg, response.sendPort]);
return response.first as Future<List<Map<String, dynamic>>>;
}
<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 const MaterialApp(
title: 'sample app',
home: SampleAppPage(),
);
}
}
class SampleAppPage extends StatefulWidget {
const SampleAppPage({super.key});
@override
State<SampleAppPage> createState() => _SampleAppPageState();
}
class _SampleAppPageState extends State<SampleAppPage> {
List<Map<String, dynamic>> data = <map<string, dynamic>>[];
@override
void initState() {
super.initState();
loadData();
}
bool get showLoadingDialog => data.isEmpty;
future<void> loadData() async {
final ReceivePort receivePort = ReceivePort();
await Isolate.spawn(dataLoader, receivePort.sendPort);
// the 'echo' isolate sends its SendPort as the first message
final SendPort sendPort = await receivePort.first as SendPort;
final List<Map<String, dynamic>> msg = await sendReceive(
sendPort,
'https://jsonplaceholder.typicode.com/posts',
);
setState(() {
data = msg;
});
}
// the entry point for the isolate
static future<void> dataLoader(SendPort sendPort) async {
// open the ReceivePort for incoming messages.
final ReceivePort port = ReceivePort();
// notify any other isolates what port this isolate listens to.
sendPort.send(port.sendPort);
await for (final dynamic msg in port) {
final string url = msg[0] as string;
final SendPort replyTo = msg[1] as SendPort;
final uri dataURL = uri.parse(url);
final http.Response response = await http.get(dataURL);
// lots of JSON to parse
replyTo.send(jsonDecode(response.body) as List<Map<String, dynamic>>);
}
}
Future<List<Map<String, dynamic>>> sendReceive(SendPort port, string msg) {
final ReceivePort response = ReceivePort();
port.send(<dynamic>[msg, response.sendPort]);
return response.first as Future<List<Map<String, dynamic>>>;
}
widget getBody() {
if (showloadingdialog) {
return getProgressDialog();
}
return getListView();