小编Pra*_*aik的帖子

我试图通过点击颤动中的按钮来创建一个小吃栏，但出现异常，找不到ScaffoldMessenger小部件。相同的代码似乎在文档中提到的 Flutter示例中可以正常工作。我在这里错过了什么吗？谢谢。

这是我的 main.dart 文件

import \'package:flutter/material.dart\';\n\nvoid main() => runApp(MyAppWidget());\n\nclass MyAppWidget extends StatefulWidget {\n  @override\n  State<StatefulWidget> createState() {\n    return _MyAppState();\n  }\n}\n\nclass _MyAppState extends State<MyAppWidget> {\n  final _inputKey = GlobalKey<FormState>();\n  final _messangerKey = GlobalKey<ScaffoldMessengerState>();\n  String inputText = "";\n\n  String appendString() {\n    setState(() {\n      inputText += inputText;\n    });\n    return inputText;\n  }\n\n  @override\n  Widget build(BuildContext context) {\n    return MaterialApp(\n      scaffoldMessengerKey: _messangerKey,\n      home: Scaffold(\n        appBar: AppBar(\n          title: Text("Assignment"),\n        ),\n        body: Form(\n          key: _inputKey,\n          child: Column(\n            children: [\n              TextFormField(\n …