A method which call an external Api return an interface

Question

I use restsharp to consume an external API. I have a class that extends the interface

public interface ICarInfo
{
    ICarDetails GetCarInfo(string car);
}

public interface ICarDetails
{
    string Color { get; set; }
    string MaxSpeed { get; set; }
    string Acceleration{ get; set; }

}

I create the class which extends this interface and implement this method using restsharp

public ICarDetails GetCarInfo(string car)
    {
        var client = new RestClient("http://xxx.xxxxxxx.com");
        var request = new RestRequest("/{car} ? access_key =xxxxxxxxx", Method.GET);
        var queryResult = client.Get<ICarDetails >(request).Data;
        return queryResult;
    }

Now i get an error in this line:

var queryResult = client.Get<ICarDetails >(request).Data;

ICarDetails must be a non-abstract type with a public parameterless constructor in order to use it as a parameter T in the generic type or method

Answer 1

A concrete class is needed in order to be able to deserialize the request data.

So refactor the definitions accordingly

public interface ICarInfo {
    CarDetails GetCarInfo(string car);
}

public class CarDetails {
    public string Color { get; set; }
    public string MaxSpeed { get; set; }
    public string Acceleration{ get; set; }
}

And the implementation

public CarDetails GetCarInfo(string car) {
    var client = new RestClient("http://xxx.xxxxxxx.com");
    var request = new RestRequest("/{car} ? access_key =xxxxxxxxx", Method.GET);
    var queryResult = client.Get<CarDetails>(request).Data;
    return queryResult;
}

Even if you insist on keeping the ICarDetails interface, you will still need a concrete implementation for deserialization.

public interface ICarInfo {
    ICarDetails GetCarInfo(string car);
}

public interface ICarDetails {
    string Color { get; set; }
    string MaxSpeed { get; set; }
    string Acceleration{ get; set; }    
}

public class CarDetails : ICarDetails {
    public string Color { get; set; }
    public string MaxSpeed { get; set; }
    public string Acceleration{ get; set; }
}

Again making sure the concrete class is used

public ICarDetails GetCarInfo(string car) {
    var client = new RestClient("http://xxx.xxxxxxx.com");
    var request = new RestRequest("/{car} ? access_key =xxxxxxxxx", Method.GET);
    var queryResult = client.Get<CarDetails>(request).Data;
    return queryResult;
}