最好的方法是使用FutureBuilder。
从FutureBuilder文档中：
new FutureBuilder<String>(
future: _calculation, // a Future<String> or null
builder: (BuildContext context, AsyncSnapshot<String> snapshot) {
switch (snapshot.connectionState) {
case ConnectionState.none: return new Text('Press button to start');
case ConnectionState.waiting: return new Text('Awaiting result...');
default:
if (snapshot.hasError)
return new Text('Error: ${snapshot.error}');
else
return new Text('Result: ${snapshot.data}');
}
},
)
另一件事是您要在State.build方法之外构建窗口小部件并保存窗口小部件本身，这是一种反模式。您实际上应该每次都在build方法中构建窗口小部件。
您可以在没有FutureBuilder的情况下使它起作用，但是您应该保存http调用的结果（经过适当处理），然后在构建函数中使用数据。
看到这一点，但请注意，使用FutureBuilder是实现此目的的更好方法，我只是向您提供此知识。
import 'dart:async';
import 'dart:convert';
import 'package:Flutter/material.dart';
void main() {
runApp(new MyApp());
}
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Flutter demo',
theme: new ThemeData(
primarySwatch: Colors.blue,
),
home: new MyHomePage(title: 'async demo'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
@override
_MyHomePageState createState() => new _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
List data;
@override
initState() {
super.initState();
new Future<String>.delayed(new Duration(seconds: 5), () => '["123", "456", "789"]').then((String value) {
setState(() {
data = json.decode(value);
});
});
}
@override
Widget build(BuildContext context) {
if (data == null) {
return new Scaffold(
appBar: new AppBar(
title: new Text("Loading..."),
),
);
} else {
return new Scaffold(
appBar: new AppBar(
title: new Text(widget.title),
),
body: new Center(
child: new ListView(
children: data
.map((data) => new ListTile(
title: new Text("one element"),
subtitle: new Text(data),
))
.toList(),
),
),
);
}
}
}
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