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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() {
bool showLoadingDialog = data.isEmpty;
if (showLoadingDialog) {
return getProgressDialog();
} else {
return getListView();
}
}
Widget getProgressDialog() {
return const Center(child: CircularProgressIndicator());
}
ListView getListView() {
return ListView.builder(
itemCount: data.length,
itemBuilder: (context, position) {
return getRow(position);
},
);
}
Widget getRow(int i) {
return Padding(
padding: const EdgeInsets.all(10),
child: Text("Row ${data[i]["title"]}"),
);
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: const Text('Sample App'),
),
body: getBody(),
);
}
}<code_end>
<topic_end>
<topic_start>
Making network requests
Making a network call in Flutter is easy when you
use the popular http package. This abstracts
away a lot of the networking that you might normally
implement yourself, making it simple to make network calls.To add the http package as a dependency, run flutter pub add:To make a network call,
call await on the async function http.get():
<code_start>Future<void> loadData() async {
final Uri dataURL = Uri.parse('https://jsonplaceholder.typicode.com/posts');
final http.Response response = await http.get(dataURL);
setState(() {
data = jsonDecode(response.body);
});
}<code_end>
<topic_end>
<topic_start>
Showing the progress on long-running tasks
In UIKit, you typically use a UIProgressView
while executing a long-running task in the background.In Flutter, use a ProgressIndicator widget.
Show the progress programmatically by controlling
when it’s rendered through a boolean flag.
Tell Flutter to update its state before your long-running task starts,
and hide it after it ends.In the example below, the build function is separated into three different
functions. If showLoadingDialog is true
(when widgets.length == 0), then render the ProgressIndicator.
Otherwise, render the ListView with the data returned from a network call.
<code_start>import 'dart:convert';
import 'package:flutter/material.dart';