在Flutter中显示SnackBar

Z时代
2024-01-10
分类：问答

我想的有状态小部件显示一个。我的应用程序使用名为 MyHomePage

的有状态小部件创建 MaterialApp的 新实例。 __

我尝试在showSnackBar（）方法中显示SnackBar。但是失败，因为’ 方法’showSnackBar’被调用为null ‘。

此代码有什么问题？

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(),
    );
  }
}
class MyHomePage extends StatefulWidget {
  MyHomePage({Key key}) : super(key: key);
  @override
  _MyHomePageState createState() => new _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
  final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();
  @override
  void initState() {
    super.initState();
    showInSnackBar("Some text");
  }
  @override
  Widget build(BuildContext context) {
    return new Padding(
            key: _scaffoldKey,
            padding: const EdgeInsets.all(16.0),
            child: new Text("Simple Text")
    );
  }
  void showInSnackBar(String value) {
    _scaffoldKey.currentState.showSnackBar(new SnackBar(
        content: new Text(value)
    ));
  }
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
        title: 'Flutter',
        theme: new ThemeData(
            primarySwatch: Colors.blue,
        ),
        home: new Scaffold(body: new MyHomePage()),
      );
  }
}
class MyHomePage extends StatefulWidget {
  MyHomePage({Key key}) : super(key: key);
  @override
  _MyHomePageState createState() => new _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
  @override
  void initState() {
    super.initState();
  }
  @override
  Widget build(BuildContext context) {
    showInSnackBar("Some text");
    return new Padding(
        padding: const EdgeInsets.all(16.0),
        child: new Scaffold(
          body: new Text("Simple Text")
        )
    );
  }
  void showInSnackBar(String value) {
    Scaffold.of(context).showSnackBar(new SnackBar(
        content: new Text(value)
    ));
  }
}