如何将对象列表转换为 map 列表

Question

有一个 Day class 和一个 Day 对象列表，我需要从这些对象的 map 转换为一个列表。

class Day{
    double open;
    double high;
    double low;
    double close;
    double volumeTo;

    Day({this.open, this.high, this.low, this.close, this.volumeTo});
}

List historical = [
    new Day(open: 42.6, high: 53.9, low: 39.5, close:56.00, volumeTo: 5000.0),
    new Day(open: 42.6, high: 53.9, low: 39.5, close:56.00, volumeTo: 5000.0),
    new Day(open: 42.6, high: 53.9, low: 39.5, close:56.00, volumeTo: 5000.0),
    new Day(open: 42.6, high: 53.9, low: 39.5, close:56.00, volumeTo: 5000.0),
];

最后我需要这样的例子：

List sampleData = [
    {"open":42.6, "high":53.9, "low":39.5, "close":56.00, "volumeto":5000.0},
    {"open":42.6, "high":53.9, "low":39.5, "close":56.00, "volumeto":5000.0},
    {"open":42.6, "high":53.9, "low":39.5, "close":56.00, "volumeto":5000.0},
    {"open":42.6, "high":53.9, "low":39.5, "close":56.00, "volumeto":5000.0},
];

Answer 1

使用map方法，如下所示：

final sampleData = historical.map((h) => {"open": h.open, "high": h.high, "low": h.low, "close": h.close, "volumeTo": h.volumeTo}).toList();

Answer 2

Day().historical.map((e)=>{<- do your conversion here ->}).toList();

Answer 3

如果您使用的是 android studio，您可以安装一个插件来帮助生成 toMap() 和 fromMap() 代码。 插件名称为Dart 数据 Class

安装插件后，像这样生成助手function

class Day{
  double open;
  double high;
  double low;
  double close;
  double volumeTo;

  Day({this.open, this.high, this.low, this.close, this.volumeTo});

  factory Day.fromMap(Map<String, dynamic> map) {
    return new Day(
      open: map['open'] as double,
      high: map['high'] as double,
      low: map['low'] as double,
      close: map['close'] as double,
      volumeTo: map['volumeTo'] as double,
    );
  }

  Map<String, dynamic> toMap() {
    // ignore: unnecessary_cast
    return {
      'open': this.open,
      'high': this.high,
      'low': this.low,
      'close': this.close,
      'volumeTo': this.volumeTo,
    } as Map<String, dynamic>;
  }
}

// this helper method helps convert to a list of Map
dynamic getListMap(List<dynamic> items) {
  if (items == null) {
    return null;
  }
  List<Map<String, dynamic>> dayItems = [];
  items.forEach((element) {
    dayItems.add(element.toMap());
  });
  return dayItems;
}

并像这样调用 function

void somthoing(){
 var listOfMap = getListMap(historical);
}