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json - Dart - 按 json 值过滤数组

问题描述

我有这个 JSON 响应：

{
    "suggestions": [
        {
            "label": "United States, <b>New York</b>",
            "language": "en",
            "countryCode": "USA",
            "locationId": "NT_rNsDLtnazM.kjVC-K6YWOA",
            "address": {
                "country": "United States",
                "state": "<b>New York</b>"
            },
            "matchLevel": "state"
        },
        {
            "label": "United States, <b>New York</b>, <b>New York</b>, <b>New York</b>",
            "language": "en",
            "countryCode": "USA",
            "locationId": "NT_YpQcXqbaOb.I4m5EW8BHEC",
            "address": {
                "country": "United States",
                "state": "<b>New York</b>",
                "county": "<b>New York</b>",
                "city": "<b>New York</b>",
                "postalCode": "10007"
            },
            "matchLevel": "city"
        },
        {
            "label": "United States, <b>New York</b>, <b>New York</b>",
            "language": "en",
            "countryCode": "USA",
            "locationId": "NT_ABhedB4xGEL83YY5az47iD",
            "address": {
                "country": "United States",
                "state": "<b>New York</b>",
                "county": "<b>New York</b>"
            },
            "matchLevel": "county"
        },
        {
            "label": "United Kingdom, NE27 0, North Shields, <b>New York</b> Way",
            "language": "en",
            "countryCode": "GBR",
            "locationId": "NT_B24AwYSzW4TK04x9UiKMoD",
            "address": {
                "country": "United Kingdom",
                "state": "England",
                "county": "Tyne and Wear",
                "city": "North Shields",
                "district": "North Shields",
                "street": "<b>New York</b> Way",
                "postalCode": "NE27 0"
            },
            "matchLevel": "street"
        },
        {
            "label": "United States, <b>New York</b>, Buffalo, <b>New York</b> State Thruway",
            "language": "en",
            "countryCode": "USA",
            "locationId": "NT_-WyF-KGZ-pqF8zQV6NegHD",
            "address": {
                "country": "United States",
                "state": "<b>New York</b>",
                "county": "Erie",
                "city": "Buffalo",
                "district": "Grant Ferry",
                "street": "<b>New York</b> State Thruway",
                "postalCode": "14213"
            },
            "matchLevel": "street"
        }
    ]
}

在代码中，我只想显示matchLevel类型为city.

到目前为止，我一直在尝试这个，但它不起作用。我在这里做错了什么？

var data = json.decode(res.body);
      var rest = data["suggestions"] as List;
      var filteredList;
      rest.forEach((val) => filteredList.add(rest.where((val) => val["matchLevel"] == "city")));
      print(filteredList);

      this.list =
          filteredList.map<Suggestions>((json) => Suggestions.fromJson(json)).toList();

也试过这个：

标签： jsonflutterdart

解决方案

改变这个：

var data = json.decode(res.body);
      var rest = data["suggestions"] as List;
      var filteredList;
      rest.forEach((val) => filteredList.add(rest.where((val) => val["matchLevel"] == "city")));
      print(filteredList);

进入这个：

var data = json.decode(res.body);
      var rest = data["suggestions"] as List;
      var filteredList;
      filteredList = rest.where((val) => val["matchLevel"] == "city");
      print(filteredList);

从文档：

此方法返回映射元素的视图。只要返回Iterable的不是迭代，提供的函数 test 就不会被调用。迭代不会缓存结果，因此对返回的结果进行多次迭代Iterable可能会在同一个元素上多次调用提供的函数测试。

因此，当您使用时forEach()，where()您将多次获得相同的结果。

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