C＃解析JSON问题

Question

我有以下JSON和我使用Json.NET（Newtonsoft.Json）：

{ 
    "total_items": "62", 
    "page_number": "6", 
    "page_size": "10", 
    "page_count": "7", 
    "cars": { 
    "car": [  
     { 
     "car_name": "Honda", 
     "engines": { 
      "engine": [ <-- HONDA has multiple engines, so this is an array 
      { 
       "name": "1.2L" 
      }, 
      { 
       "name": "1.8L" 
      } 
      ] 
     }, 
     "country": "Japan" 
     "image": { 
      "thumb": { 
       "url": "http://image_path/Honda.jpg" <-- Image provided 
      } 
     } 
     }, 
     { 
     "car_name": "Ford", 
     "engines": { 
      "engine": { <-- FORD has single engine, so this is an object 
       "name": "2.2L" 
      } 
     }, 
     "country": "Japan" 
     "image": null <-- image is null 
     }, 
     { 
     "car_name": "VW", 
     "engines": null, <-- VW has no engines, so this is null 
     "country": "Germany" 
     "image": null <-- image is null 
     } 
    ] 
    } 
} 

而且我有以下Car对象：

class Car 
{ 
    public Car() { } 

    public string Name { get; set; } 
    public string Country { get; set; } 
    public List<String> EngineNames { get; set; } 
} 

我需要处理所有以上3种情况（HONDA阵列，FORD对象阵列，VW空白阵列）。如果它不为空，则获取所有引擎名称。因此，例如上面，我EngineNames列表中3辆汽车将是：

Honda.EngineNames = {"1.2L", "1.8L"} // array in JSON 
Ford.EngineNames = {"2.2L"} //object in JSON 
VW.EngineNames = null //null in JSON 

我需要解析上面的JSON得到车资料。我解析car_name和国家，但我不知道如何通过处理上述3种情况来解析所有引擎名称。

private Cars GetCars(string json) 
{ 
    dynamic data = (JObject)JsonConvert.DeserializeObject(json); 

    foreach (dynamic d in data.cars.car) 
    { 
     Car c = new Car(); 

     c.Name = (string)d.SelectToken("car_name"); 
     c.Country = (string)d.SelectToken("country"); 

     // PROBLEM: This works fine for array or null in JSON above (HONDA and VW), but it errors on JSON object (in case of FORD) 
     // When handling FORD, I get error "'Newtonsoft.Json.Linq.JProperty' does not contain a definition for 'name'" 
     c.EngineNames = (d.engines != null ? ((IEnumerable)d.engines.engine).Cast<dynamic>().Select(e => (string)e.name) : null); 

     CarList.Add(c); 
    } 
    return CarList; 
} 

Answer 1

使用从here转换器（最初提出的重复，但这个问题曾与JSON其他一些问题）

你的类结构有待修改了一下。

望着这JSON：

"cars": { <-- cars is an object, not an array 
    "car": [ <-- the cars object actually contains the array 
     { 
     "car_name": "Honda", 
     "engines": { <-- same goes for this 
      "engine": [ 
      { 

因此，你需要写包装类，以正确反映了JSON。下面是我想出什么用：

public class Root 
{ 
    public CarHolder Cars {get;set;} 
} 
public class CarHolder 
{ 
    public IList<Car> Car { get; set; } 
} 
public class Car 
{ 
    public Car() { } 

    public string car_name { get; set; } 
    public string Country { get; set; } 

    public EngineHolder Engines { get; set; } 
} 
public class EngineHolder 
{ 
    [JsonConverter(typeof(SingleOrArrayConverter<Engine>))] 
    public List<Engine> Engine { get; set; } 
} 
public class Engine 
{ 
    public string Name { get; set; } 
} 

而且使用转换从上面的问题：

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

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer) 
    { 
     JToken token = JToken.Load(reader); 
     if (token.Type == JTokenType.Array) 
     { 
      return token.ToObject<List<T>>(); 
     } 
     return new List<T> { token.ToObject<T>() }; 
    } 

    public override bool CanWrite 
    { 
     get { return false; } 
    } 

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

用法：

var result = JsonConvert.DeserializeObject<Root>(jsonStr); 
Console.WriteLine(result.Cars.Car[0].Engines.Engine[0].Name == "1.2L"); 
Console.WriteLine(result.Cars.Car[0].Engines.Engine[1].Name == "1.8L"); 
Console.WriteLine(result.Cars.Car[1].Engines.Engine[0].Name == "2.2L"); 
Console.WriteLine(result.Cars.Car[2].Engines == null); 

所有打印true

通过循环汽车&发动机

foreach(var car in result.Cars.Car) 
{ 
    if (car.Engines != null) 
    { 
     foreach(var engine in car.Engines.Engine) 
     { 
      var engineName = engine.Name; 
     } 
    } 
} 

Answer 2

你应该可以使用它作为你的类结构;

public class Rootobject 
{ 
    public string total_items { get; set; } 
    public string page_number { get; set; } 
    public string page_size { get; set; } 
    public string page_count { get; set; } 
    public Cars cars { get; set; } 
} 

public class Cars 
{ 
    public Car[] car { get; set; } 
} 

public class Car 
{ 
    public string car_name { get; set; } 
    public Engines engines { get; set; } 
    public string country { get; set; } 
} 

public class Engines 
{ 
    public object engine { get; set; } 
} 

//I created below class manually 
public class Engine 
{ 
    public string name { get; set; } 
} 

我用VS的内置功能来生成这个。脚步;

1. 打开一个新的cs文件。
2. 复制您的JSON
3. 转到编辑菜单>粘贴特殊
4. 选择粘贴JSON作为类

一旦做到这一点，它应该只是一个创建了两个方法，序列化的问题，并反序列化。

与还原序列化/ deserialise方法

 private static T Deserialise<T>(string json) 
     { 
      var myopject = JsonConvert.DeserializeObject<T>(json); 
      return myopject; 
     } 

     private static string Serialise<T>(T value) 
     { 
      var mycontent = JsonConvert.SerializeObject(value); 
      return mycontent; 
     } 

我们测试上面的方法更新，你可以做到这一点。

  var jsonstring = @"{ 
       ""total_items"": ""62"", 
       ""page_number"": ""6"", 
       ""page_size"": ""10"", 
       ""page_count"": ""7"", 
       ""cars"": { 
       ""car"": [ 
        { 
        ""car_name"": ""Honda"", 
        ""engines"": { 
         ""engine"": [ 
         { 
          ""name"": ""1.2L"" 
         }, 
         { 
          ""name"": ""1.8L"" 
         } 
         ] 
        }, 
        ""country"": ""Japan"" 
        }, 
        { 
        ""car_name"": ""Ford"", 
        ""engines"": { 
         ""engine"": { 
         ""name"": ""2.2L"" 
         } 
        }, 
        ""country"": ""Japan"" 
        }, 
        { 
        ""car_name"": ""VW"", 
        ""engines"": null, 
        ""country"": ""Germany"" 
        } 
       ] 
       } 
      }"; 
      var myobject = Deserialise<Rootobject>(jsonstring); 

      //if you want to parse engines you can do something like this. 

      if (myobject.cars != null && myobject.cars.car != null && myobject.cars.car.Any()) 
     { 
      foreach (Car car in myobject.cars.car) 
      { 
       if (car.engines != null && car.engines.engine != null) 
       { 
        bool isList = false; 
        try 
        { 
         var eng = Deserialise<Engine>(car.engines.engine.ToString()); 
        } 
        catch 
        { 
         isList = true; 
        } 
        if (isList) 
        { 
         try 
         { 
          var eng = Deserialise<List<Engine>>(car.engines.engine.ToString()); 
         } 
         catch 
         { 
          Debug.WriteLine("Not a list"); 
         } 
        } 
       } 
      } 
     } 

      var myjson = Serialise(myobject);