在無狀態小部件中創建的變量不能在子小部件中使用（Flutter）

Question

我對 Flutter 很陌生，我遇到了一個問題。 你或許能幫上忙！

錯誤信息是：

Undefined name 'myObjectList'.
Try correcting the name to one that is defined, or defining the name.

和代碼：

void main() => runApp(MyApp());

class myObject {
  const myObject({this.objectName, this.added, this.price});

  // final int id;
  // final int userId;
  final String objectName;
  // final String category;
  // final DateTime purchase;
  final DateTime added;
  final double price;
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {

    // Mock data for objects (later to be retrieved from back-end)
    const List<myObject> myObjectList = [
      const myObject(objectName: 'TV', added: null, price: 12.25),
      const myObject(objectName: 'Nintendo Switch', added: null, price: 122)
    ];

    return MaterialApp(
      title: "The Safe",
      home: objectInventory(),
      theme: ThemeData(primaryColor: Colors.blueGrey),
    );
  }
}

class objectInventory extends StatefulWidget {
  _objectInventoryState createState() => _objectInventoryState();
}

class _objectInventoryState extends State<objectInventory> {
  Widget build(BuildContext context) {
    return Scaffold(appBar: AppBar(title: Text('The Safe')), body: myObjectList);
  }
} // End of _objectInventoryState

我想將我的模擬數據定義到 MyApp class 中。 事實上，稍后，我想在應用啟動時從后端檢索數據。 有沒有辦法讓這些數據“全球化”？

謝謝

Answer 1

myObjectList在方法體內部聲明，您應該在外部聲明它，在 class 內部

像這樣：

List<myObject> myObjectList = new List<myObject>();

更新

在 state 中，您可以使用小部件字段訪問StatlessWidget實例。 所以它變成了這樣：

.... body: this.widget.myObjectList   ....

Answer 2

如果我在所有函數/類之外定義列表，它會起作用。 這樣做，我可以從任何地方訪問它，並且可以在特定的 class 中填充列表。

就我而言，列表的初始加載將在 class 'MyApp' 中完成。

void main() => runApp(MyApp());

class myObject {
  myObject({this.objectName, this.added, this.price});

  // final int id;
  // final int userId;
  final String objectName;
  // final String category;
  // final DateTime purchase;
  final DateTime added;
  final double price;

}

List<myObject> myObjectList = new List<myObject>();

class MyApp extends StatelessWidget {
  @override

  Widget build(BuildContext context) {

    //List<myObject> myObjectList = new List<myObject>();
    // Mock data for objects (later to be retrieved from back-end)
    myObjectList.add(
      myObject(objectName: 'TV', added: null, price: 12.25)
    );
    myObjectList.add(
      myObject(objectName: 'Nintendo Switch', added: null, price: 122)
    );

    return MaterialApp(
      title: "The Safe",
      home: objectInventory(),
      theme: ThemeData(primaryColor: Colors.blueGrey),
    );
  }
}

class objectInventory extends StatefulWidget {
  objectInventoryState createState() => objectInventoryState();
}

class objectInventoryState extends State<objectInventory> {
  Widget build(BuildContext context) {
    return Scaffold(appBar: AppBar(title: Text('The Safe')), body: Text(myObjectList[1].objectName) );
  }
}

謝謝