無法將JSON數組反序列化爲類型 - Json.NET

Question

我想將json數據反序列化爲模型類，但是我失敗了。這是我做的：

public CountryModel GetCountries() { 

     using (WebClient client = new WebClient()) { 

      var result = client.DownloadString("http://api.worldbank.org/incomeLevels/LIC/countries?format=json"); 

      var output = JsonConvert.DeserializeObject<List<CountryModel>>(result); 

      return output.First(); 
     } 
    } 

這是我的模型看起來像：

public class CountryModel 
{ 
    public int Page { get; set; } 
    public int Pages { get; set; } 
    public int Per_Page { get; set; } 
    public int Total { get; set; } 

    public List<Country> Countries { get; set; } 
} 

public class Country 
{ 
    public int Id { get; set; } 
    public string Iso2Code { get; set; } 
    public string Name { get; set; } 
    public Region Region { get; set; } 
} 

public class Region 
{ 
    public int Id { get; set; } 
    public string Value { get; set; } 
} 

你可以看到JSON的我正在這裏：http://api.worldbank.org/incomeLevels/LIC/countries?format=json

這是我的錯誤：

無法將JSON數組反序列化爲類型'Mvc4AsyncSample.Models.CountryModel'。 1號線，位置1

Answer 1

你必須編寫自定義JsonConverter：

public class CountryModelConverter : JsonConverter 
    { 

     public override bool CanConvert(Type objectType) 
     { 
      if (objectType == typeof(CountryModel)) 
      { 
       return true; 
      } 

      return false; 
     } 

     public override object ReadJson(JsonReader reader, Type objectType 
      , object existingValue, JsonSerializer serializer) 
     { 
      reader.Read(); //start array 
      //reader.Read(); //start object 
      JObject obj = (JObject)serializer.Deserialize(reader); 

      //{"page":1,"pages":1,"per_page":"50","total":35} 
      var model = new CountryModel(); 

      model.Page = Convert.ToInt32(((JValue)obj["page"]).Value); 
      model.Pages = Convert.ToInt32(((JValue)obj["pages"]).Value); 
      model.Per_Page = Int32.Parse((string) ((JValue)obj["per_page"]).Value); 
      model.Total = Convert.ToInt32(((JValue)obj["total"]).Value); 

      reader.Read(); //end object 

      model.Countries = serializer.Deserialize<List<Country>>(reader); 

      reader.Read(); //end array 

      return model; 
     } 

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

有了這樣的轉換器標記的CountryModel（我也不得不改用一些int到string）：

[JsonConverter(typeof(CountryModelConverter))] 
    public class CountryModel 
    { 
     public int Page { get; set; } 
     public int Pages { get; set; } 
     public int Per_Page { get; set; } 
     public int Total { get; set; } 

     public List<Country> Countries { get; set; } 
    } 

    public class Country 
    { 
     public string Id { get; set; } 
     public string Iso2Code { get; set; } 
     public string Name { get; set; } 
     public Region Region { get; set; } 
    } 

    public class Region 
    { 
     public string Id { get; set; } 
     public string Value { get; set; } 
    } 

那麼你應該能夠像這樣反序列化：

var output = JsonConvert.DeserializeObject<CountryModel>(result); 

Answer 2

這看起來像一個（不是很好）嘗試在JSON中表示XML。該JSON看起來是這樣的：

[ 
    { 
    "page": 1, 
    … 
    }, 
    [ 
    { 
     "id": "AFG", 
     "name": "Afghanistan", 
     … 
    }, 
    { 
     "id": "BDI", 
     "name": "Burundi", 
     … 
    }, 
    … 
    ] 
] 

在一個合理的JSON（即順帶映射到模型很好）應該是這樣的：

{ 
    "page": 1, 
    …, 
    "countries": [ 
    { 
     "id": "AFG", 
     "name": "Afghanistan", 
     … 
    }, 
    { 
     "id": "BDI", 
     "name": "Burundi", 
     … 
    }, 
    … 
    ] 
} 

如果您確定要使用JSON（和不是XML），則可以通過先反序列化JSON到JSON.NET的對象模型做出來，然後反序列化到模型：

var json = client.DownloadString("http://api.worldbank.org/incomeLevels/LIC/countries?format=json"); 

var array = (JArray)JsonConvert.DeserializeObject(json); 

var serializer = new JsonSerializer(); 

var countryModel = serializer.Deserialize<CountryModel>(array[0].CreateReader()); 

countryModel.Countries = serializer.Deserialize<List<Country>>(array[1].CreateReader()); 

return countryModel; 

不要忘記設置Id屬性string，因爲那就是他們。

Answer 3

您的模型與JSON結構不匹配。看起來你錯過了最後6個屬性。

{ 
"id": "AFG", 
"iso2Code": "AF", 
"name": "Afghanistan", 
"region": { 
    "id": "SAS", 
    "value": "South Asia" 
}, 
"adminregion": { 
    "id": "SAS", 
    "value": "South Asia" 
}, 
"incomeLevel": { 
    "id": "LIC", 
    "value": "Low income" 
}, 
"lendingType": { 
    "id": "IDX", 
    "value": "IDA" 
}, 
"capitalCity": "Kabul", 
"longitude": "69.1761", 
"latitude": "34.5228" 

}