Flutter 中的 List <Map<String, dynamic>> 到 DropdownMenuItem

FullCurrencyList我在一个单独的文件中有一个类currencies.dart，我尝试在第二个页面上导入它，然后构建一个 DropdownMenuItem 小部件。

现在我收到以下错误：

The argument type 'List<DropdownMenuItem<FullCurrencyList>>' can't be assigned to the parameter type 'List<DropdownMenuItem<String>>?'

class FullCurrencyList {
  static final List<Map<String, dynamic>> currencies = <Map<String, dynamic>>[
    <String, dynamic>{
      "code": "USD",
      "name": "United States Dollar",
    }
  ];
}

这是我的完整代码：

import 'package:flutter/material.dart';
import 'package:brain/util/currencies.dart';

class Page3 extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => new _Page3State();
}

class _Page3State extends State<Page3> {

  String? _valCurrency;
  List<Map<String, dynamic>> _currencyList = FullCurrencyList.currencies;

  @override
  void initState() {
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: <Widget>[
        Container(
          child: Text(("Please, select your currency:"),
          ),
        ),
        new Row(
          children: <Widget>[
            Container(
              child: Text(("Currency") + ":",
              )
            ),
            Container(
              child: DropdownButton<String>(
                borderRadius:BorderRadius.circular(10),
                hint: Text("Select"),
                value: _valCurrency,
                items: _currencyList.map<DropdownMenuItem<FullCurrencyList>>((FullCurrencyList value) {
                  return DropdownMenuItem<FullCurrencyList>(
                    value: value,
                     child: Text(value.name + ' ' + value.code),
                  );
                }).toList(),
                onChanged: (String? value) {
                  setState(() {
                     _valCurrency = value!;
                  });
                },
              ),
            ),
        ]),
    ]);
  }
}