Dart：无法访问嵌套的地图对象 [英] Dart: Can't access to nested map object

问题描述

我正在创建Flutter应用程序，但无法访问 dart 中的嵌套地图对象。
我的代码如下。

I am creating a Flutter application and I can't access to nested map object in dart. My code is as below.

 Map<String, String> _localizedValues;

  Future<bool> load() async {
    // Load a language JSON file from the 'i18n' folder
    String value = await rootBundle.loadString('i18n/${locale.languageCode}.json');
    Map<String, dynamic> jsonMap = jsonDecode(value);
    _localizedValues = jsonMap.map((key, value) {
      return MapEntry(key, value.toString());
    });
    return true;
  }

  String translate(String parent, String key) {
    // Returns a localized text
    return _localizedValues[parent][key];
  }

发生错误 [key] 这部分。它说

不能将参数类型'String'分配给参数类型'int'。

The argument type 'String' can't be assigned to the parameter type 'int'.

JSON文件就是这样。

JSON file is like this.

{
     "Parent": {
         "key": "key"
     }
 }

这有什么问题？

推荐答案

我将针对此问题提出另一种解决方案更方便您使用。
您可以在使用多维json对象之前先对其进行展平。

I will propose a different solution to this problem that might be easier for you to work with. You can simply flatten the multidimensional json object before working with it.

Map<String, String> _localizedValues;

Map flattenTranslations(Map<String, dynamic> json, [String prefix = '']) {
    final Map<String, String> translations = {};
    json.forEach((String key, dynamic value) {
      if (value is Map) {
        translations.addAll(flattenTranslations(value, '$prefix$key.'));
      } else {
        translations['$prefix$key'] = value.toString();
      }
    });
    return translations;
  }

  Future<bool> load() async {
    // Load a language JSON file from the 'i18n' folder
    String value = await rootBundle.loadString('i18n/${locale.languageCode}.json');
    Map<String, dynamic> jsonMap = jsonDecode(value);
    _localizedValues = flattenTranslations(jsonMap);
    return true;
  }

您将获得一个简单的Map对象，其中包含json的所有键

You will get a simple Map object that will contain all the keys of your json with every subtree key prefixed by their parent's key.

例如：

    {
  "Parent": {
    "key": "key",
    "key1": "key",
    "key2": "key",
    "key3": "key",
    "someOtherKey": {
      "key213": "keyeye",
      "oneMoreLevel": {
        "key123412": "asdasdasd"
      }
    }
  }
}

将转换为包含 Parent.someOtherKey.oneMoreLevel.key123412键的地图。
之后，您可以使用此函数获取翻译：

Will convert to a map with "Parent.someOtherKey.oneMoreLevel.key123412" key included. After this you can use this function to get the translation:

    String translate(String key) {
    // Returns a localized text or KEY if there's no localization
    return _localizedValues[key] ?? key;
  }

print(translate('Parent.someOtherKey.oneMoreLevel.key123412'));

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