Question

I’d like to deserialize a JSON string which I get from a webservice. My problem is, that the deserialized object class array (of type Result) has always 0 items in it….

But the webservice returns the correct string.
So I think the failure occurs in the way how I deserialize the string/stream.

Any ideas what’s my fault?

//JSON result string:

{"Results":
    [{"Result":{
     "Name":"Rechnung2",
     "Date1":"2012-10-05",
     "Item1":"50",
     "Item2":"10",
     "CompanyName":"Contoso",
     "Description":"My description"}}]
}    


[DataContract]
public class Result
{
    [DataMember]
    public string Name { get; set; }
    [DataMember]
    public string Date1 { get; set; }
    [DataMember]
    public string Item1 { get; set; }
    [DataMember]
    public string Item2 { get; set; }
    [DataMember]
    public string CompanyName { get; set; }
    [DataMember]
    public string Description { get; set; }
}

public async void GetjsonStream()
    {
        HttpClient client = new HttpClient();
        string url = "http://localhost/test/api.php?format=json&key=12345";
        HttpResponseMessage response = await client.GetAsync(url);

        //ReadAsStringAsync() works fine, so I think ReadAsStreamAsync() works also fine
        var str = await response.Content.ReadAsStreamAsync();

        DataContractJsonSerializer ser = new DataContractJsonSerializer(typeof(Result[]));

        //Result has always 0 items
        Result[] res = (Result[])ser.ReadObject(str);
    }

Answer 1

I haven’t used DataContractJsonSerializer myself, so this may not be the best approach – but I suspect that the problem is that the JSON represents “an object containing a collection of results” – not “a collection of results”.

Try this, in addition to your existing code:

[DataContract]
public class ResultCollection
{
    [DataMember]
    public Result[] Results { get; set; }
}

...

var ser = new DataContractJsonSerializer(typeof(ResultCollection));
var collection = (ResultCollection)ser.ReadObject(str);
var results = collection.Results;

You may be able to change the type of Results to List<Result> too, if that’s helpful.

(I’ve just tried the code above, and it gave me the right result, so it looks like this is at least along the right lines…)