JSON string encoded twice?

问题

My Web API (code that generates JSON) is generating the following JSON string. It seems, if I am not wrong, that it has been encoded twice:

"\"[{\\\"SportID\\\":1,\\\"SportName\\\":\"Tennis\\\"},{\"SportID\\\":2,\\\"SportName\\\":\\\"Footbal\\\"},{\"SportID\\\":3,\"SportName\":\\\"Swimming\\\"}]\""

Web API code:

public string JSONTest()
{
    List<Sport> sports = new List<Sport>();
    sports.Add(new Sport() { SportID = 1, SportName = "Tennis" });
    sports.Add(new Sport() { SportID = 2, SportName = "Footbal" });
    sports.Add(new Sport() { SportID = 3, SportName = "Swimming" });

    try
    {      
      return JsonConvert.SerializeObject(sports);        
    }
    catch (Exception ex) { }            
}

Sport class:

public class Sport { public int SportID { get; set; } public string SportName { get; set; } }

Screenshot of getting JSON:

The following line gives me an error, I think because of twice encoding:

var JavaScriptSerializerResult = (new JavaScriptSerializer()).Deserialize< List<Sport>>(jsonResponse);

I get the same error if try with this:

  var jsonConvertResult = JsonConvert.DeserializeObject<List<Sport>>(jsonResponse);

How can I fix my Web API to not encode twice, or if that is not the problem, how can I decode this JSON?

回答1:

I think you should try JsonConvert.DeserializeObject to deserialize the JSON:

public class Sport
{
    // Dummy "Sport" class as it was not mentioned by OP.
    public int SportID { get; set; }
    public string SportName { get; set; }
}

I get serialized JSON as:

Deserialized it:

string json = JSONTest();
var obj = JsonConvert.DeserializeObject<List<Sport>>(json);

Output:

UPDATE:

As per OP's shared JSON (which is being received from server), encoding can be removed by using:

private string RemoveEncoding(string encodedJson)
{
    var sb = new StringBuilder(encodedJson);
    sb.Replace("\\", string.Empty);
    sb.Replace("\"[", "[");
    sb.Replace("]\"", "]");
    return sb.ToString();
}

Deserialize it by:

string js = "\"[{\\\"SportID\\\":1,\\\"SportName\\\":\"Tennis\\\"},{\"SportID\\\":2,\\\"SportName\\\":\\\"Footbal\\\"},{\"SportID\\\":3,\"SportName\":\\\"Swimming\\\"}]\"";

string res = RemoveEncoding(js);
var obj = JsonConvert.DeserializeObject<List<Sport>>(res);

回答2:

Shorter sample for json.net library.
Here, entity is my serializable C# object. I use JsonConvert along with some formatting and specify to ignore reference looping to prevent circular referencing.

using Newtonsoft.Json;
var json = JsonConvert.SerializeObject (entity, Formatting.Indented, 
           new JsonSerializerSettings {ReferenceLoopHandling = ReferenceLoopHandling.Ignore,
    });

回答3:

Use Linq Query Concept:

  public string JSONTest()
    { List<Sport> sports = new List<Sport>();
                    sports.Add(new Sport() { SportID = 1, SportName = "Tennis" });
    sports.Add(new Sport() { SportID = 2, SportName = "Footbal" });
    sports.Add(new Sport() { SportID = 3, SportName = "Swimming" });
                    var result_sports = (from row in sports
                                           group row by new { row.SportID , row.SportName} into hdr
                                           select new Sport()
                                           {
                                               SportID  = hdr.Key.SportID ,
                                               SportName  = hdr.Key.SportName ,

                                           }).ToList();
                    string jsondata = new JavaScriptSerializer().Serialize(result_sports);
}

回答4:

Summary: Your return object is being serialized twice. Remove your hand-rolled serialization code and return objects from your web services - not JSON strings.

---

Your JSON is indeed being serialized 'twice'. Look closely at this screenshot and we see escaped quote marks:

Your list properly serialized should produce a JSON string something like this:

[{"SportID":1,"SportName":"Tennis"},{"SportID":2,"SportName":"Footbal"},{"SportID":3,"SportName":"Swimming"}]

But we have something more like this:

"[{\"SportID\":1,\"SportName\":\"Tennis\"},{\"SportID\":2,\"SportName\":\"Footbal\"},{\"SportID\":3,\"SportName\":\"Swimming\"}]"

I can replicate this (code below) and it means that your JSON string has itself been fed through a serializer.

This is almost certainly due to you manually serializing your List<Sport>. You don't need to do that. Web API serializes for you - hence the second run through a serializer.

Change the return type of your Web API function if necessary, and then instead of writing:

return JsonConvert.SerializeObject(sports);

just do

return sports;

Web API will take care of the serialization and you will no longer have the bothersome quotes and escape characters.

---

Code dump I tested with:

void Main()
{
    string json = JSONTest();
    Console.WriteLine(json);
    var obj = JsonConvert.DeserializeObject<List<Sport>>(json);

    string jsonX2 = JsonConvert.SerializeObject(json);
    Console.WriteLine(jsonX2);
    obj = JsonConvert.DeserializeObject<List<Sport>>(jsonX2); // exception
}

public string JSONTest()
{
    List<Sport> sports = new List<Sport>();
    sports.Add(new Sport() { SportID = 1, SportName = "Tennis" });
    sports.Add(new Sport() { SportID = 2, SportName = "Footbal" });
    sports.Add(new Sport() { SportID = 3, SportName = "Swimming" });

    return JsonConvert.SerializeObject(sports);
}

public class Sport
{
    public int SportID { get; set; }
    public string SportName { get; set; }
}

来源：https://stackoverflow.com/questions/48919380/json-string-encoded-twice