如何在 Dart 中将对象转换为数组（映射）？答案

【问题标题】：How to convert an object to array (map) in Dart?如何在 Dart 中将对象转换为数组（映射）？
【发布时间】：2015-02-08 22:32:48
【问题描述】：

如何在 Dart 中将 Object 类型转换为 Map 类型（数组），使变量成为键/值对？

【问题讨论】：

标签： arrays object reflection dart type-conversion

【解决方案1】：

/**
   * Uses refection (mirrors) to produce a Map (array) from an object's
   * variables. Making the variable name the key, and it's value the
   * value.
   */
  Map objectToMap(Object object)
  {
    // Mirror the particular instance (rather than the class itself)
    InstanceMirror instanceMirror = reflect(object);
    Map dataMapped = new Map();

    // Mirror the instance's class (type) to get the declarations
    for (var declaration in instanceMirror.type.declarations.values)
    {
      // If declaration is a type of variable, map variable name and value
      if (declaration is VariableMirror)
      {
        String variableName = MirrorSystem.getName(declaration.simpleName);
        String variableValue = instanceMirror.getField(declaration.simpleName).reflectee;

        dataMapped[variableName] = variableValue;
      }
    }

    return dataMapped;
  }

【讨论】：

请注意，这对于服务器端代码是可以的，但不建议使用带有 dart2js 的镜像。 smoke 包可以帮助解决这个用例。它在 Dartium 中运行时使用镜像，但在 dart2js 中运行时使用代码生成。

【解决方案2】：

将递归地将任何 JS 对象转换为 Dart 映射、列表或标量值：

/// js_interop.dart
import 'dart:js';

/// Converts the specified JavaScript [value] to a Dart instance.
dynamic convertToDart(value) {
  // Value types.
  if (value == null) return null;
  if (value is bool || value is num || value is DateTime || value is String) return value;

  // JsArray.
  if (value is Iterable) return value.map(convertToDart).toList();

  // JsObject.
  return new Map.fromIterable(getKeysOfObject(value), value: (key) => convertToDart(value[key]));
}

/// Gets the enumerable properties of the specified JavaScript [object].
List<String> getKeysOfObject(JsObject object) => (context['Object'] as JsFunction).callMethod('keys', [object]);

用法：

/// config.js
window.$environment = 'staging';
window.$config = {
  name: 'FooBar',
  params: {
    assets: ['css', 'js'],
    forceSsl: true
  }
};

/// main.dart
import 'dart:js' as js;
import 'js_interop.dart';

void main() {
  var environment = convertToDart(js.context[r'$environment']);
  assert(environment is String);
  assert(environment == 'staging');

  var config = convertToDart(js.context[r'$config']);
  assert(config is Map<String, dynamic>);
  assert(config.length == 2);

  assert(config['name'] is String);
  assert(config['name'] == 'FooBar');

  assert(config['params'] is Map<String, dynamic>);
  assert(config['params'].length == 2);

  assert(config['params']['forceSsl'] is bool);
  assert(config['params']['forceSsl'] == true);

  assert(config['params']['assets'] is List<String>);
  assert(config['params']['assets'].length == 2);
  assert(config['params']['assets'].first == 'css');
  assert(config['params']['assets'].last == 'js');
}

注意事项：创建的实例不反映原始 JS 对象的更改。如果您需要此功能，请参阅：https://stackoverflow.com/a/20720378/1084485

【讨论】：