相关疑难解决方法(0)

我想在Flutter的有状态小部件中显示一个简单的SnackBar.我的应用程序使用名为MyHomePage的有状态窗口小部件创建MaterialApp的新实例.

我尝试在showSnackBar()方法中显示SnackBar.但它失败的' 方法'showSnackBar'在null上被调用 '.

这段代码出了什么问题？

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) …

我想在我的 Flutter 应用程序中显示 SnackBar。我已阅读文档并复制它：\n
我的脚手架主体：

Widget build(BuildContext context) {\n    return WillPopScope(\n      onWillPop: () async => false,\n      child: Scaffold(\n        appBar: AppBar(\n          centerTitle: true,\n          title: Text("Oszt\xc3\xa1lyok"),\n          leading: Padding(\n              padding: const EdgeInsets.only(left: 5.0),\n              child: IconButton(\n                  icon: Icon(Icons.exit_to_app, color: Colors.white70),\n                  onPressed: () {\n                    authService.signOut();\n                    authService.loggedIn = false;\n                    Navigator.push(\n                        context,\n                        MaterialPageRoute(\n                            builder: (context) => GoogleSignUp()));\n                  })),\n          actions: <Widget>[\n            Padding(\n                padding: const EdgeInsets.only(right: 5.0),\n                child: Row(\n                  children: <Widget>[\n                    IconButton(\n                        icon: Icon(Icons.add_circle_outline,\n                            color: Colors.white70),\n                        onPressed: () {\n                          createPopup(context);\n                        }),\n//                    IconButton(\n//                        icon: Icon(Icons.search, color: Colors.black38),\n//                        onPressed: null),\n …