我是 Flutter 和 Dart 的新手,我正在尝试构建一个在屏幕上显示设备信息的 Flutter 应用程序。为此,我试图从这里使用这个库:'device_info':https://pub.dartlang.org/packages/device_info#-readme-tab-
在 MyApp 类的“build”方法中,我试图从“device_info”包中实例化对象并调用一个恰好是异步属性的属性。由于默认的构建方法不是异步的,那么如何在构建方法中调用这个属性呢?以下是我的代码:
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
DeviceInfoPlugin deviceInfoPlugin = DeviceInfoPlugin();
AndroidDeviceInfo androidDeviceInfo = await deviceInfoPlugin.androidInfo;
return MaterialApp(
title: 'My Device Info',
home: Scaffold(
appBar: AppBar(
title: Text('My Device Info'),
),
body: Center(
child: Text('Device model:' + 'Moto'),
),
),
);
}
}
最佳答案
我建议你使用 FutureBuilder
:
import 'package:flutter/material.dart';
class MyApp extends StatefulWidget {
@override
_MyAppState createState() => _MyAppState();
}
class _MyAppState extends State<MyApp> {
// save in the state for caching!
DeviceInfoPlugin _deviceInfoPlugin;
@override
void initState() {
super.initState();
_deviceInfoPlugin = DeviceInfoPlugin();
}
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'My Device Info',
home: Scaffold(
appBar: AppBar(
title: Text('My Device Info'),
),
body: FutureBuilder<AndroidDeviceInfo>(
future: _deviceInfoPlugin.androidInfo,
builder: (BuildContext context, AsyncSnapshot<AndroidDeviceInfo> snapshot) {
if (!snapshot.hasData) {
// while data is loading:
return Center(
child: CircularProgressIndicator(),
);
} else {
// data loaded:
final androidDeviceInfo = snapshot.data;
return Center(
child: Text('Android version: ${androidDeviceInfo.version}'),
);
}
},
),
),
);
}
}
通常,当使用 FutureBuilder
或 Future
s 时,您必须记住,封闭的小部件可以随时重建(例如,因为设备被旋转,或显示键盘)。这意味着再次调用 build
方法。
在这种特殊情况下,这不是问题,因为插件会缓存该值并立即返回它,但一般来说,您永远不应该在 build
中创建或获取 Future
> 方法。相反,从 initState
或点击事件处理程序执行:
import 'package:flutter/material.dart';
class FooWidget extends StatefulWidget {
@override
_FooWidgetState createState() => _FooWidgetState();
}
class _FooWidgetState extends State<FooWidget> {
Future<int> _bar;
@override
void initState() {
super.initState();
_bar = doSomeLongRunningCalculation();
}
void _retry() {
setState(() {
_bar = doSomeLongRunningCalculation();
});
}
@override
Widget build(BuildContext context) {
return Column(
children: <Widget>[
FutureBuilder<int>(
future: _bar,
builder: (BuildContext context, AsyncSnapshot<int> snapshot) {
if (snapshot.hasData) {
return Text('The answer to everything is ${snapshot.data}');
} else {
return Text('Calculating answer...');
}
},
),
RaisedButton(
onPressed: _retry,
child: Text('Retry'),
)
],
);
}
}
Future<int> doSomeLongRunningCalculation() async {
await Future.delayed(Duration(seconds: 5)); // wait 5 sec
return 42;
}
https://stackoverflow.com/questions/53800662/