Question

我在使用JSON.NET解析Last.FM API JSON时遇到问题。问题在于字符串值是空的，就像：http://ws.audioscrobbler.com/2.0/?method=artist.getinfo&artist=ASASAS&api_key=53aed44f6fa2ee83d40324232594e1d9&format=json

中的类似标签一样

否则，对象格式正确：http://ws.audioscrobbler.com/2.0/?method=artist.getinfo&artist=Kamelot&api_key=53aed44f6fa2ee83d40324232594e1d9&format=json

[JsonConverter(typeof(StringNullConverter<Tags>))]
public class Tags
{
            public List<Tag> tag { get; set; }
}

  internal class StringVacioConverter<T> : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return (objectType == typeof(string)) || (objectType == typeof(List<string>));
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        if (reader.TokenType == JsonToken.String)
        {
            return null;
        }
        else { return serializer.Deserialize<T>(reader); }
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {

    }
}

但是，这不起作用，它在尝试返回serializer时进入无限循环。反序列化......

Answer 1

此代码适用于您的两个json字符串（只有 JsonConvert.DeserializeObject 需要一些自定义Converter的帮助（请参阅下面的 MyConverter ）。）

var lastfm = LastFM.Deserialize(json);

public class LastFM
{
    public class Image
    {
        [JsonProperty("#text")]
        public string text { get; set; }
        public string size { get; set; }
    }

    public class Stats
    {
        public string listeners { get; set; }
        public string playcount { get; set; }
    }

    public class Similar
    {
        public List<Artist> artist { get; set; }
    }

    public class Tag
    {
        public string name { get; set; }
        public string url { get; set; }
    }

    public class Tags
    {
        public List<Tag> tag { get; set; }
    }

    public class Link
    {
        [JsonProperty("#text")]
        public string text { get; set; }
        public string rel { get; set; }
        public string href { get; set; }
    }

    public class Links
    {
        public Link link { get; set; }
    }

    public class Bio
    {
        public Links links { get; set; }
        public string published { get; set; }
        public string summary { get; set; }
        public string content { get; set; }
    }

    public class Artist
    {
        public string name { get; set; }
        public string mbid { get; set; }
        public string url { get; set; }
        public List<Image> image { get; set; }
        public string streamable { get; set; }
        public string ontour { get; set; }
        public Stats stats { get; set; }
        public Similar similar { get; set; }
        public Tags tags { get; set; }
        public Bio bio { get; set; }
    }

    public class RootObject
    {
        public Artist artist { get; set; }
    }

    public static RootObject Deserialize(string s)
    {
        return JsonConvert.DeserializeObject<RootObject>(s, new MyConverter());
    }

    class MyConverter : JsonConverter
    {

        public override bool CanConvert(Type objectType)
        {
            return objectType == typeof(Similar) ||
                    objectType == typeof(Tags);
        }

        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        {
            if (reader.Value is string && String.IsNullOrWhiteSpace((string)reader.Value)) return null;
            return reader.Value;
        }

        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        {
            throw new NotImplementedException();
        }
    }
}

Answer 2

尝试像这样调整转换器：

// I. here we inherit from more sophisticated class, created for us
internal class StringNullConverter<T> : CustomCreationConverter<T>
    where T : new()
{
    // II. thanks the new() constraint we can override this method easily
    public override T Create(Type objectType)
    {
        return new T();
    }

    public override bool CanConvert(Type objectType)
    {
        return (objectType == typeof(string)) || (objectType == typeof(List<string>));
    }

    // III. here we pass the rest to smart base
    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        if (reader.TokenType == JsonToken.String)
        {
            return null;
        }
        // this is the correct implementation
        return base.ReadJson(reader, objectType, existingValue, serializer);

    }
    // unchanged
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {

    }
}

我们从Newtonsoft.Json的全部力量中获利，这为我们带来了许多预先实施的东西

在C＃JSON.NET中将String或对象解析为对象

2 个答案: