RangeError（索引）：无效值：不在包含范围 0..2:3 内

Question

嘿伙计们，我正在尝试制作一个应用程序，以示例方式跟踪比特币价格......但它在 android-emulator 中给了我错误，但代码本身没有任何错误，我不知道出了什么问题，

我认为问题出在 DropdownMenuItem 列表中，但我无法获取它

谁能帮忙，谢谢

class PriceScreen extends StatefulWidget {
  @override
  _PriceScreenState createState() => _PriceScreenState();
}

class _PriceScreenState extends State<PriceScreen> {
  String selectedCurrency = 'EGP';
  List<DropdownMenuItem<String>> getDropdownItems() {
    List<DropdownMenuItem<String>> dropdownItems = [];

    for (int i = 0; i < currenciesList.length; i++) {
      String currency = (cryptoList[i]);
      var newItem = DropdownMenuItem(
        child: Text(currency),
        value: currency,
      );
      dropdownItems.add(newItem);
    }
    return dropdownItems;
  }

  @override
  Widget build(BuildContext context) {
    getDropdownItems();
    return Scaffold(
      appBar: AppBar(
        title: Text(' Coin Ticker'),
      ),
      body: Column(
        mainAxisAlignment: MainAxisAlignment.spaceBetween,
        crossAxisAlignment: CrossAxisAlignment.stretch,
        children: <Widget>[
          Padding(
            padding: EdgeInsets.fromLTRB(18.0, 18.0, 18.0, 0),
            child: Card(
              color: Colors.lightBlueAccent,
              elevation: 5.0,
              shape: RoundedRectangleBorder(
                borderRadius: BorderRadius.circular(10.0),
              ),
              child: Padding(
                padding: EdgeInsets.symmetric(vertical: 15.0, horizontal: 28.0),
                child: Text(
                  '1 BTC = ? USD',
                  textAlign: TextAlign.center,
                  style: TextStyle(
                    fontSize: 20.0,
                    color: Colors.white,
                  ),
                ),
              ),
            ),
          ),
          Container(
            height: 150.0,
            alignment: Alignment.center,
            padding: EdgeInsets.only(bottom: 30.0),
            color: Colors.lightBlue,
            child: DropdownButton<String>(
                value: selectedCurrency,
                items: getDropdownItems(),
                onChanged: (value) {
                  setState(() {
                    selectedCurrency = value!;
                  });
                }),
          ),
        ],
      ),
    );
  }
}

android 模拟器：

Answer 1

for 循环应该检查您正在访问的数组的长度。

因此，它应该是这个

 for (int i = 0; i < currenciesList.length; i++) {
      String currency = (currenciesList[i]);
 }

或

for (int i = 0; i < cryptoList.length; i++) {
      String currency = (cryptoList[i]);
 }

RangeError（索引）：无效值：不在包含范围 0..2:3 内

RangeError (index) : invalid calue : not in incusive range 0..2:3

flutter

dart

flutter-layout

flutter-dependencies

dart-null-safety