如何根據用戶在Flutter中輸入的數字前綴更改影像

我是 Flutter 的新手。我想根據用戶輸入的數字前綴更改字串“operatorIcon”的影像，但我下面的代碼不起作用。影像仍然沒有改變

這是我的模特

    class PrefixOperator {
  final String id;
  final String name;
  final String image;
  final List<PrefixList> prefixList;

  PrefixOperator({
    required this.id,
    required this.name,
    required this.image,
    required this.prefixList,
  });
}

class PrefixList {
  final String id;
  final String code;

  PrefixList({
    required this.id,
    required this.code,
  });
}

List<PrefixOperator> prefixOperator = [
  PrefixOperator(
    id: "1",
    name: "aaa",
    image: AssetsCollection.icAaa,
    prefixList: prefixAaa,
  ),
  PrefixOperator(
    id: "2",
    name: "bbb",
    image: AssetsCollection.icBbb,
    prefixList: prefixBbb,
  ),
  
];

List<PrefixList> prefixAaa = [
  PrefixList(id: "1", code: "0711"),
  PrefixList(id: "2", code: "0712"),
  PrefixList(id: "3", code: "0713"),
];

List<PrefixList> prefixBbb = [
  PrefixList(id: "1", code: "0614"),
  PrefixList(id: "2", code: "0615"),
  PrefixList(id: "3", code: "0616"),
];

這是我的有狀態小部件

    final TextEditingController _controller = TextEditingController();
  String phoneNumber = "";
  bool isContains = false;
  String prefixNumber = "";
  String operatorIcon = "";

  handleTextChange() {
    if (_controller.text != "" && _controller.text.length > 8) {
      setState(() {
        prefixNumber = _controller.text.substring(0, 4);
      });
    }
  }

  checkIcon() {
    if (prefixNumber != "") {
      prefixOperator.map((item) {
        isContains =
            item.prefixList.map((e) => e.code).toList().contains(prefixNumber);

        if (isContains == true) {
          setState(() {
            operatorIcon = item.name;
          });
        }
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      crossAxisAlignment: CrossAxisAlignment.center,
      children: [
        Row(children: [
          Image.asset(operatorIcon != "" ? operatorIcon : widget.icon,
              height: 40),
          Expanded(
            child: Column(
              children: [
                SizedBox(
                  height: 10,
                ),
                InputLabel(
                  labelText: "Phone Number",
                  isRequired: false,
                ),
                TextField(
                  controller: _controller,
                  onChanged: (value) {
                    handleTextChange();
                    checkIcon();
                  },
                  keyboardType: TextInputType.phone,
                  decoration: InputDecoration(
                    hintText: 'Enter your mobile number',
                  ),
                ),
              ],
            ),
          )
        ]),
      ],
    );
  }

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uj5u.com熱心網友回復：

你知道這map不是一個void函式嗎？

Iterable<T> map<T>(T toElement(E e)) sync* {
  for (var value in this) {
    yield toElement(value);
  }
}

map is 回傳一個新的惰性 Iterable，其中包含通過按迭代順序在此 Iterable 的每個元素上呼叫 toElement 創建的元素。

所以，你錯過了什么。只需.toList()在您的第一張地圖上做廣告。你會得到價值。

 prefixOperator.map((item) {
    isContains =
        item.prefixList.map((e) => e.code).toList().contains(prefixNumber);
    ....

  }).toList();  // add this 

我在 dartpad 上測驗過。它作業正常

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