Web Api .Net Client - Object not deserialising

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C#

web

API

Hi all,

This is a follow on from the following question I asked yesterday:
Return complex objects with Web API[^]
Thanks very much to KornfeldEliyahuPeter[^] for his help there.

I'm now creating a console application to access the Web Api. I have used Calling-a-web-api-from-a-net-client[^] from Microsoft as my template for creating my client but I'm getting an issue when it tries to de-serialise my object.

To save having to jump between questions here is my object structure:

public interface IMyFileInterface
{
    string FileName {get;set;}
    MyEnum FileType {get;set;
    DateTime UploadDate {get;set;}
}

Classes:

[DataContract]
[KnownType(typeof(FooFileModel))]
public class ReturnModel
{
   [DataMember]
   public string Name {get;set;}
   [DataMember]
   public List<IMyFileInterface> LatestFiles {get;set;}
}

[DataContract]
public class FooFileModel : IMyFileInterface
{
    [DataMember]
    string FileName {get;set;}
    [DataMember]
    MyEnum FileType {get;set;
    [DataMember]
    DateTime UploadDate {get;set;}

}

My api call is to an address similar to: "http://localhost:12345/API/API/GetReport"

My client code looks like this:

private async Task<UtilitiesReportModel> GetReportModalAsync()
{
   using (var client = new HttpClient())
   {
          client.BaseAddress = new Uri("http://localhost:12345/");
          client.DefaultRequestHeaders.Accept.Clear();
          client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

                Task<HttpResponseMessage> response =  client.GetAsync("API/API/GetReport");
                if (response.Result.IsSuccessStatusCode)
                {
                    UtilitiesReportModel reportModel = await response.Result.Content.ReadAsAsync<UtilitiesReportModel>();
                    Debug.WriteLine(reportModel.Name);
                    Debug.WriteLine(reportModel.LatestUploads.Count);
                    return reportModel;
                }
                return null;

            }
        }

Which is called from my "main" method as follows:

var res = GetReportModalAsync();
res.Wait();
var theRes = res.Result;

However, when res.Wait() triggers I get the following error:

Could not create an instance of type Common.Objects.IMyFileInterface. Type is an interface or abstract class and cannot be instantiated. Path 'LatestUploads[0].SurveyType', line 1, position 220.

(I don't know if it is relevant but SurveyType is a custom enum).

Now I understand what the error says, for some reason when it tries to de-serialise it is trying to create an instance of an interface, as we all know this is impossible. How do I tell it to create an instance of it's original class? When I look at the response from the API call it has the original data type in.

Any help would be appreciated as I would like to be able to code against interfaces and not hard code the classes if I can help it.

When I call the api in a web browser it displays the result in the following XML. (I know the comment has asked for it in JSon).

<ReportModel xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.datacontract.org/2004/07/Common.Objects">
    <CurrentMonth i:nil="true"/>
    <LastRefresh>0001-01-01T00:00:00</LastRefresh>
    <LatestUploads xmlns:d2p1="http://schemas.microsoft.com/2003/10/Serialization/Arrays">
        <d2p1:anyType i:type="FooFileModel">
            <DateTimeUploaded>2014-12-08T14:23:37.243</DateTimeUploaded>
            <FileName>05122014 cleaned for loading.xlsx</FileName>
            <NumberOfEntries>76</NumberOfEntries>
            <SurveyType>TypeA</SurveyType>
        </d2p1:anyType>
        <d2p1:anyType i:type="FooFileModel">
            <DateTimeUploaded>2014-12-05T12:04:47.877</DateTimeUploaded>
            <FileName>04122014 Cleaned for loading.xlsx</FileName>
            <NumberOfEntries>5</NumberOfEntries>
            <SurveyType>TypeB</SurveyType>
        </d2p1:anyType>
        <d2p1:anyType i:type="FooFileModel">
            <DateTimeUploaded>2014-12-05T12:05:28.14</DateTimeUploaded>
            <FileName>04122014 Cleaned for loading.xlsx</FileName>
            <NumberOfEntries>6</NumberOfEntries>
            <SurveyType>TypeC</SurveyType>
        </d2p1:anyType>
    </LatestUploads>
    <Name>Site1</Name>
</ReportModel>

If I call "response.Result.Content.ReadAsStringAsync();

I get the following out, which I believe is the Json response:

{"$type":"Common.Objects.ReportModel, Common",
"Name":"Site1",
"LatestUploads":[
    {"$type":"Common.Objects.FooFileModel, Common",
     "SurveyType":2,
     "FileName":"08122014 Cleaned for loading.xlsx",
     "DateTimeUploaded":"2014-12-09T14:02:36.147",
     "NumberOfEntries":69},
    {"$type":"Common.Objects.FooFileModel, Common",
     "SurveyType":1,
     "FileName":"08122014 Cleaned for loading.xlsx",
     "DateTimeUploaded":"2014-12-09T14:03:41.11",
     "NumberOfEntries":11},
    {"$type":"Common.Objects.FooFileModel, Common",
     "SurveyType":2,
     "FileName":"05122014 cleaned for loading.xlsx",
     "DateTimeUploaded":"2014-12-08T14:23:37.243",
     "NumberOfEntries":76}],
"CurrentMonth":null,"LastRefresh":"0001-01-01T00:00:00"}