flutter - LateInitializationError: 字段 'roast' 尚未初始化

Question

我正在尝试构建一个颤振应用程序以在特定的硬编码“烘焙”值之间随机选择，并将它们添加到位于卡片中的 listtile 中。我有三个不在任何类中的变量，这样我就可以在每个小部件和函数中访问它们。然后我试图在一个函数中为其分配一个值，但是当我运行应用程序时，我得到了错误：

══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
The following LateError was thrown building MyHomePage(dirty, state: _MyHomePageState#8da4b):
LateInitializationError: Field 'roast' has not been initialized.

有谁知道我能做什么？

这是一些代码 -

T getRandomElement<T>(List<T> list) {
  final random = new Random();
  var i = random.nextInt(list.length);
  return list[i];
}

getElement() {
  var element = getRandomElement(roastList);
  var randRoast = [
    roastList[element.id].roast,
  ];
  var randAuthor = [
    roastList[element.id].author,
  ];
  var randCategory = [roastList[element.id].category];
  roast = randRoast.toString();
  author = randAuthor.toString();
  category = randCategory.toString();
}

烤的例子 -

 Roast(
      10 (id) ,
      'roast',
      'author of roast',
      RoastCategory.category),

我的主页 -

late String roast;
late String author;
late String category;

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Roast'),
        centerTitle: true,
        backgroundColor: Colors.red,
      ),
      body: Center(
          child: Column(
        children: [
          Card(
            child: Row(
              children: [
                ListTile(
                  title: Text(roast),
                  subtitle: Text(author),
                )
              ],
            ),
          ),
          ElevatedButton(
              onPressed: () {
                getElement();
              },
              child: Text('print')),
        ],
      )),
    );
  }
}

标签： flutterdartdart-null-safety