将 Json 对象反序列化为没有 typeNameHandling 的多态 C# 对象

Question

我的问题是我想将一个 json 对象反序列化为一个 C# 对象，但诀窍是 C# 对象包含 List<抽象类> 并且这个抽象类是另外 10 个类的超类。

public sealed class SearchAPIResult
{
    public string Status;

    public SearchAPIQuery Query;

    public SearchResults Result;

    public SearchAPIResult()
    {

    }

    public SearchAPIResult(string status)
    {
        Status = status;
    }
}

并且SearchAPIResult是：

public sealed class SearchResults
{
    public string TextAnswer;

    public List<APIResultWidget> Items;

    public SearchResults()
    {
        Items = new List<APIResultWidget>();
    }
}

这里的对象APIResultWidget是一个抽象类，它继承了大约 10 个类。

问题是 JSON 对象没有自动（如 JSON.NET 中的 typeNameHandling）来引导反序列化器转换到 10 个派生类中的哪个对象。相反，对象由两个字段标记：Type 和 SubType... 如下所示

{
    "Status": "OK",
    "Query": {
        "Query": "this is a query",
        "QueryLanguage": "EN"
    },
    "Result": {
        "TextAnswer": "This is your text answer",
        "Items": [{
                "Type": "list",
                "SubType": null,
                "Title": null,
                "Items": []
            }, {
                "Type": "text",
                "Content": "this is some content"
            }
        ]
    }
}

在前面的json对象中，Result列表包含两个对象，一个：

{
    "Type": "list",
    "SubType": null,
    "Title": null,
    "Items": []
}

它映射到一个 listWidget 类型的类（它继承自抽象APIResultWidget和两个：

{
    "Type": "text",
    "Content": "this is some content"
}

它映射到textWidget也继承自同一个抽象类的类

当我使用 Json.NET 方式时

SearchAPIResult converted = (SearchAPIResult)JsonConvert.DeserializeObject(json, typeof(SearchAPIResult), new JsonSerializerSettings { TypeNameHandling = TypeNameHandling.Auto });

它抛出以下异常：

无法创建 Kngine.API.APIResultWidget 类型的实例。类型是接口或抽象类，不能被实例化。路径“Result.Items[0].Type”，第 1 行，位置 136。

我猜有一种自定义方法可以指出该类型是由字段 Type 和 SubType 定义的，并为 Converter 提供自定义类型注释器，对吗？

Answer 1

实际上我实现的解决方案是非常基本的解决方案，我从 System.Web.Extentions 扩展了 JavaScriptConverter 类，我实现了 deserialize 方法，该方法自动接收原始对象中的每个小 json 对象作为字典，我只需填写根据对象本身的字段，这有点手动方式，但这是我能想到并且有效的唯一解决方案，自定义类实现如下所示：

class myCustomResolver  : JavaScriptConverter

{
    public override object Deserialize(IDictionary<string, object> dictionary, Type type, JavaScriptSerializer serializer)
    {
        if (type == typeof(APIResultWidget))
        {
            switch ((string)dictionary["Type"])
            {
                case "weather":
                    {
                        WeatherWidget x = new WeatherWidget();
                        x.Location = (string)dictionary["Location"];
                        x.Current = (CurrentWeather)dictionary["Current"];
                        //x.Forcast = (List<WeatherForcastItem>)dictionary["Forcast"];

                        System.Collections.ArrayList itemss = ((System.Collections.ArrayList)dictionary["Forcast"]);
                        foreach (var item in itemss)
                        {
                            x.Forcast.Add(serializer.ConvertToType<WeatherForcastItem>(item));
                        }

                        return x;
                    };
                case "text":
                    {
                        TextWidget x = new TextWidget();
                        x.Content = (string)dictionary["Content"];
                        return x;
                    }; 
                case "keyValueText":
                    {
                        KeyValueTextWidget x = new KeyValueTextWidget();
                        x.Key = (string)dictionary["Key"];
                        x.Key = (string)dictionary["Value"];
                        x.Key = (string)dictionary["ValueURL"];
                        return x;
                    };
                case "keyValuesText":
                    {
                        KeyValuesTextWidget x = new KeyValuesTextWidget();
                        x.Key = (string)dictionary["Key"];
                        //x.Values = (List<ValueItem>)dictionary["ValueItem"];

                        System.Collections.ArrayList itemss = ((System.Collections.ArrayList)dictionary["ValueItem"]);
                        foreach (var item in itemss)
                        {
                            x.Values.Add(serializer.ConvertToType<ValueItem>(item));
                        }


                        return x;


                    }; 
                case "url":
                    {
                        URLWidget x = new URLWidget();
                        x.ThumbnailImageURL = (string)dictionary["ThumbnailImageURL"];
                        x.Title = (string)dictionary["Title"];
                        x.URL = (string)dictionary["URL"];
                        x.HTMLContent = (string)dictionary["HTMLContent"];
                        return x;

                    }; 
                case "map":
                    {
                        MapWidget x = new MapWidget();
                        System.Collections.ArrayList itemss = ((System.Collections.ArrayList)dictionary["Pins"]);
                        foreach (var item in itemss)
                        {
                            x.Pins.Add(serializer.ConvertToType<MapPoint>(item));
                        }

                        //x.Pins = (List<MapPoint>)dictionary["Pins"];
                        return x;

                    }; 
                case "image":
                    {
                        ImageWidget x = new ImageWidget();
                        x.Title = (string)dictionary["Title"];
                        x.ImageURL = (string)dictionary["ImageURL"];
                        x.ThumbnailURL = (string)dictionary["ThumbnailURL"];
                        x.PageURL = (string)dictionary["PageURL"];
                        return x;
                    }; 
                case "html":
                    {
                        HTMLWidget x = new HTMLWidget();
                        x.Title = (string)dictionary["Title"];
                        x.HTML = (string)dictionary["HTML"];
                        return x;


                    }; 
                case "entity":
                    {
                        EntityWidget x = new EntityWidget();
                        x.SubType = (string)dictionary["SubType"];
                        x.Title = (string)dictionary["Title"];
                        x.Abstract = (string)dictionary["Abstract"];
                        x.ImageURL = (string)dictionary["ImageURL"];
                        x.Url = (string)dictionary["Url"];
                        return x;

                    }; 
                case "chart":
                    {
                        ChartWidget x = new ChartWidget();
                        x.Title = (string)dictionary["Title"];
                        //x.Categories = (List<string>)dictionary["Categories"];
                        System.Collections.ArrayList itemss = ((System.Collections.ArrayList)dictionary["Categories"]);
                        foreach (var item in itemss)
                        {
                            x.Categories.Add(serializer.ConvertToType<string>(item));
                        }



                        System.Collections.ArrayList itemss2 = ((System.Collections.ArrayList)dictionary["Data"]);
                        foreach (var item in itemss2)
                        {
                            x.Data.Add(serializer.ConvertToType<ChartsData>(item));
                        }

                        //x.Data = (List<ChartsData>)dictionary["Data"];
                        return x;
                    }; 
                case "businessEntity":
                    {
                        BusinessEntityWidget x = new BusinessEntityWidget();
                        x.SubType = (string)dictionary["SubType"];
                        x.Title = (string)dictionary["Title"];
                        x.Abstract = (string)dictionary["Abstract"];
                        x.ImageURL = (string)dictionary["ImageURL"];
                        x.URL = (string)dictionary["URL"];
                        //x.Attributes = (List<KeyValueTextWidget>)dictionary["Attributes"];
                        System.Collections.ArrayList itemss = ((System.Collections.ArrayList)dictionary["Attributes"]);
                        foreach (var item in itemss)
                        {
                            x.Attributes.Add(serializer.ConvertToType<KeyValueTextWidget>(item));
                        }

                        x.Address = (string)dictionary["Address"];
                        x.Phone = (string)dictionary["Phone"];
                        x.Lat = (double)dictionary["Lat"];
                        x.Lng = (double)dictionary["Lng"];


                        System.Collections.ArrayList itemss2 = ((System.Collections.ArrayList)dictionary["OtherURLs"]);
                        foreach (var item in itemss2)
                        {
                            x.OtherURLs.Add(serializer.ConvertToType<URLWidget>(item));
                        }
                        //x.OtherURLs = (List<URLWidget>)dictionary["OtherURLs"];

                        return x;



                    }; 

                case "list":
                    {
                        switch ((string)dictionary["SubType"])
                        {
                            case null:
                                {
                                    ListWidget x = new ListWidget();
                                    x.Title = (string)dictionary["Title"];
                                    System.Collections.ArrayList itemss = ((System.Collections.ArrayList)dictionary["Items"]);
                                    foreach (var item in itemss)
                                    {
                                        x.Items.Add(serializer.ConvertToType<APIResultWidget>(item));
                                    }
                                    return x;

                                }; 
                            case "videos":
                                {
                                    ListOfVideosWidget x = new ListOfVideosWidget();

                                    System.Collections.ArrayList itemss = ((System.Collections.ArrayList)dictionary["Items"]);
                                    foreach (var item in itemss)
                                    {
                                        x.Items.Add(serializer.ConvertToType<URLWidget>(item));
                                    }
                                    return x;
                                }; 
                            case "images":
                                {
                                    ListOfImagesWidget x = new ListOfImagesWidget();


                                    System.Collections.ArrayList itemss = ((System.Collections.ArrayList)dictionary["Items"]);
                                    foreach (var item in itemss)
                                    {
                                        x.Items.Add(serializer.ConvertToType<ImageWidget>(item));
                                    }
                                    return x;
                                }; 
                            case "webResults":
                                {

                                    ListOfWebsitesWidget x = new ListOfWebsitesWidget();

                                    System.Collections.ArrayList itemss = ((System.Collections.ArrayList)dictionary["Items"]);
                                    foreach (var item in itemss)
                                    {
                                        x.Items.Add(serializer.ConvertToType<URLWidget>(item));
                                    }
                                    return x;
                                }; 
                            case "businesses":
                                {
                                    ListOfBusinessesWidget x = new ListOfBusinessesWidget();
                                    x.Title = (string)dictionary["Title"];
                                    System.Collections.ArrayList itemss = ((System.Collections.ArrayList)dictionary["Items"]);
                                    foreach (var item in itemss)
                                    {
                                        x.Items.Add(serializer.ConvertToType<BusinessEntityWidget>(item));
                                    }
                                    return x;
                                }; 



                        }
                    }; break;


            }
        }

        else //in case of objects not inheriting from the abstract class, in this case we identify each one by something else, not "type"
        {
            if (dictionary.ContainsKey("Day")) //WeatherForcastItem
            {
                WeatherForcastItem x = new WeatherForcastItem();
                x.Day = (string)dictionary["Day"];
                x.Hi = (string)dictionary["Hi"];
                x.Lo = (string)dictionary["Lo"];
                x.Status = (string)dictionary["Status"];
                x.IconURL = (string)dictionary["IconURL"];
                return x;

            }
            else if (dictionary.ContainsKey("Temprature")) // CurrentWeather
            {
                CurrentWeather x = new CurrentWeather();
                x.Temprature = (string)dictionary["Temprature"];
                x.Status = (string)dictionary["Status"];
                x.WindSpeed = (string)dictionary["WindSpeed"];
                x.WindDirection = (string)dictionary["WindDirection"];
                x.Humidity = (string)dictionary["Humidity"];
                x.IconURL = (string)dictionary["IconURL"];
                x.IsNight = (string)dictionary["IsNight"];
                return x;

            }
            else if (dictionary.ContainsKey("Lat")) //MapPoint
            {
                MapPoint x = new MapPoint();
                x.Title = (string)dictionary["Title"];
                x.Lat = (double)dictionary["Lat"];
                x.Lng = (double)dictionary["Lng"];
                return x;
            }
            else if (dictionary.ContainsKey("Value")) //ValueItem
            {
                ValueItem x = new ValueItem();
                x.Value = (string)dictionary["Value"];
                x.ValueURL = (string)dictionary["ValueURL"];
                return x;
            }
            else if (dictionary.ContainsKey("name")) //ChartsData
            {
                ChartsData x = new ChartsData();
                x.name = (string)dictionary["name"];
                System.Collections.ArrayList itemss = ((System.Collections.ArrayList)dictionary["name"]);
                foreach (var item in itemss)
                {
                    x.values.Add(serializer.ConvertToType<string>(item));
                }
                return x;
            }
        }
        return null;
    }

    public override IDictionary<string, object> Serialize(
 object obj,
 JavaScriptSerializer serializer)
    { return null; }

    private static readonly Type[] _supportedTypes = new[]
{
    typeof( APIResultWidget )
};

    public override IEnumerable<Type> SupportedTypes
    {
        get { return _supportedTypes; }
    }

}

应该将每个 json 对象映射到它正确的类，那么反序列化器的使用相当简单：

var serializer = new JavaScriptSerializer();
serializer.RegisterConverters(new[] { new myCustomResolver() });
var dataObj = serializer.Deserialize<SearchAPIResult>(response);

这解决了我在抽象类中遇到的反序列化问题，因为它首先完全解决了类之间的相互关系。我不知道这是否是最正确的解决方案，但至少它解决了我的问题