RestSharp showing Error Cannot create interface instance to manually deserialize

I have RestSharp (which is similar to HttpClient) calls and returns data from the Web Api method

I get this error {"Cannot create an instance of an interface."}

My code is as follows:

 public List<Interest> GetInterests() { var request = new RestRequest(apiPath + "GetInterests", Method.GET) { RequestFormat = DataFormat.Json }; var response = Client.Execute<List<Interest>>(request); return response.Data; } 

Below is my answer. Content

Now the problem is that DATA exists as JSON in the Content property of the response object. I can manually deserialize it from there. But it was automatically deserializing it into a Data property before, I'm not sure what is happening now.

If I manually deserialize json, it works, but why do I need it?

 List<Interest> results = JsonConvert.DeserializeObject<List<Interest>>(response.Content); 

Answer:

"StatusCode: OK, Content-Type: application/json; charset=utf-8, Content-Length: 5597)"

JSON code is back

 [ { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":1, "InterestName":"Nursing", "AddDate":"2016-07-01T17:03:21.61", "ModDate":"2016-07-01T17:03:21.64", "AddUser":"System", "ModUser":"System", "IsDeleted":false }, { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":2, "InterestName":"Creating/Supporting Networks of Community Partners", "AddDate":"2016-07-01T17:03:21.61", "ModDate":"2016-07-01T17:03:21.64", "AddUser":"System", "ModUser":"System", "IsDeleted":false }, { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":3, "InterestName":"Epidemiology", "AddDate":"2016-07-01T17:03:21.61", "ModDate":"2016-07-01T17:03:21.64", "AddUser":"System", "ModUser":"System", "IsDeleted":false }, { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":4, "InterestName":"Maternal", "AddDate":"2016-07-01T17:03:21.61", "ModDate":"2016-07-01T17:03:21.64", "AddUser":"System", "ModUser":"System", "IsDeleted":false }, { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":5, "InterestName":"Healthcare for the Homeless", "AddDate":"2016-07-01T17:03:21.61", "ModDate":"2016-07-01T17:03:21.64", "AddUser":"System", "ModUser":"System", "IsDeleted":false }, { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":6, "InterestName":"HIV/AIDS, STD", "AddDate":"2016-07-01T17:03:21.61", "ModDate":"2016-07-01T17:03:21.64", "AddUser":"System", "ModUser":"System", "IsDeleted":false }, { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":7, "InterestName":"Nutrition", "AddDate":"2016-07-01T17:03:21.61", "ModDate":"2016-07-01T17:03:21.64", "AddUser":"System", "ModUser":"System", "IsDeleted":false }, { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":8, "InterestName":"Physical Activity", "AddDate":"2016-07-01T17:03:21.61", "ModDate":"2016-07-01T17:03:21.64", "AddUser":"System", "ModUser":"System", "IsDeleted":false }, { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":9, "InterestName":"Oral Health", "AddDate":"2016-07-01T17:03:21.61", "ModDate":"2016-07-01T17:03:21.64", "AddUser":"System", "ModUser":"System", "IsDeleted":false }, { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":10, "InterestName":"Public Health Communication", "AddDate":"2016-07-01T17:03:21.61", "ModDate":"2016-07-01T17:03:21.64", "AddUser":"System", "ModUser":"System", "IsDeleted":false }, { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":11, "InterestName":"Emergency Preparedness and Response", "AddDate":"2016-07-01T17:03:21.61", "ModDate":"2016-07-01T17:03:21.64", "AddUser":"System", "ModUser":"System", "IsDeleted":false }, { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":12, "InterestName":"Public Health Policy", "AddDate":"2016-07-01T17:03:21.61", "ModDate":"2016-07-01T17:03:21.64", "AddUser":"System", "ModUser":"System", "IsDeleted":false }, { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":13, "InterestName":"Tuberculosis", "AddDate":"2016-07-01T17:03:21.61", "ModDate":"2016-07-01T17:03:21.64", "AddUser":"System", "ModUser":"System", "IsDeleted":false }, { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":14, "InterestName":"Teen Pregnancy Prevention", "AddDate":"2016-07-01T17:03:21.61", "ModDate":"2016-07-01T17:03:21.64", "AddUser":"System", "ModUser":"System", "IsDeleted":false }, { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":15, "InterestName":"Vital Registration", "AddDate":"2016-07-01T17:03:21.61", "ModDate":"2016-07-01T17:03:21.64", "AddUser":"System", "ModUser":"System", "IsDeleted":false }, { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":16, "InterestName":"Chronic Disease", "AddDate":"2016-07-01T17:03:21.61", "ModDate":"2016-07-01T17:03:21.64", "AddUser":"System", "ModUser":"System", "IsDeleted":false }, { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":17, "InterestName":"Finance & Management", "AddDate":"2016-07-01T17:03:21.61", "ModDate":"2016-07-01T17:03:21.64", "AddUser":"System", "ModUser":"System", "IsDeleted":false }, { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":18, "InterestName":"Quality Improvement", "AddDate":"2016-07-01T17:03:21.61", "ModDate":"2016-07-01T17:03:21.64", "AddUser":"System", "ModUser":"System", "IsDeleted":false }, { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":19, "InterestName":"Healthy Community Design", "AddDate":"2016-07-01T17:03:21.61", "ModDate":"2016-07-01T17:03:21.64", "AddUser":"System", "ModUser":"System", "IsDeleted":false }, { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":20, "InterestName":"Behavioral Health and Healthcare Integration", "AddDate":"2016-07-01T17:03:21.61", "ModDate":"2016-07-01T17:03:21.64", "AddUser":"System", "ModUser":"System", "IsDeleted":false }, { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":21, "InterestName":"Rx Drug Misuse and Abuse", "AddDate":"2016-07-01T17:03:21.61", "ModDate":"2016-07-01T17:03:21.64", "AddUser":"System", "ModUser":"System", "IsDeleted":false }, { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":22, "InterestName":"Injury Prevention", "AddDate":"2016-07-01T17:03:21.61", "ModDate":"2016-07-01T17:03:21.64", "AddUser":"System", "ModUser":"System", "IsDeleted":false }, { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":23, "InterestName":"School Health", "AddDate":"2016-07-01T17:03:21.61", "ModDate":"2016-07-01T17:03:21.64", "AddUser":"System", "ModUser":"System", "IsDeleted":false }, { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":24, "InterestName":"Worksite Wellness", "AddDate":"2016-07-01T17:03:21.61", "ModDate":"2016-07-01T17:03:21.64", "AddUser":"System", "ModUser":"System", "IsDeleted":false }, { "InternInterests":[ ], "OfficeInterests":[ ], "InterestId":25, "InterestName":"Access to Healthy Foods", "AddDate":"2016-08-03T08:10:45.4", "ModDate":"2016-08-03T08:10:45.4", "AddUser":"System", "ModUser":"System", "IsDeleted":false } ] 

If I manually deserialize json, it works, but why do I need it?

 List<Interest> results = JsonConvert.DeserializeObject<List<Interest>>(response.Content); 
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1 answer

I ran into the same problem. In my case, I created a custom object (in your case, an Interest object) that had a list of ICollection objects. Thus, I delete this ICollection and make it as a List of objects. Check if any property related to the interface is of interest, and try to make it as a property of a specific object.

Check the InternInterests and OfficeInterests property, it can use any collection of interfaces.

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