C# convert List to List

Question

I would appreciate your help. I have been struggling with this for way too long.

I could easily get around this by creating two separate model classes with a duplicate list of properties, but I'd like to learn how to achieve this with the base class. So, an IntSensor and ExtSensor are both a Sensor. From another class I parse a json file with all of the data and that works great. But, trying to call a method that returns a List<Sensor> baseclass and trying to cast it as either subclass is killing me. What am I doing wrong... or is there a better way? Thank you!

PS: this may look like a duplicate question, but I tried the other solutions and they are marked in the `Repository class' as "//seen on other StackOverflow Posts -- fails" in the code.

//Model classes

public class Device
{
    public string IP { get; set; }   
    public string Name { get; set; }
    public IList<IntSensor> InternalSensors { get; set; }
    public IList<ExtSensor> ExternalSensors { get; set; }
}

public class Sensor
{
    public string Name { get; set; }
    public string ActualTemp { get; set; }
    public string HighTemp { get; set; }
    public string LowTemp { get; set; }
}

public class IntSensor : Sensor {}
public class ExtSensor : Sensor {}

//Business Class -- parsing json

public class ParseJsonData
{
    public static RoomAlertModel GetRoomAlertModel(JObject jsonTree)
    {
        RoomAlertModel model = new RoomAlertModel();
        model.IP = jsonTree["ip"].ToString();
        model.Name = jsonTree["name"].ToString();

        return model;
    }

    public static List<Sensor> GetSensors(JToken jToken)
    {
        var sensors = new List<Sensor>();

        try
        {
            foreach (var item in jToken)
            {
                var s = new Sensor();
                s.Label = item["lab"].ToString();
                s.ActualTemp = item["tf"] != null ? item["tf"].ToString() : "";
                s.HighTemp = item["hf"] != null ? item["hf"].ToString() : "";
                s.LowTemp = item["lf"] != null ? item["lf"].ToString() : "";

                sensors.Add(s);
            }
        }
        catch (Exception)
        {
        }            

        return sensors;
    }
}

//Repository

public class RoomAlertRepository
    {
        internal RoomAlertModel Retreive()
        {
            var filePath = HostingEnvironment.MapPath(@"~/App_Data/RoomAlertsData.json");

            var json = File.ReadAllText(filePath);

            JObject jsonTree = JObject.Parse(json);
            var internalSensorTree = jsonTree["internal_sen"];
            var externalSensorTree = jsonTree["sensor"];

            var model = ParseJsonData.GetRoomAlertModel(jsonTree);

            var baseList = ParseJsonData.GetSensors(internalSensorTree);

            //seen on other StackOverflow Posts -- fails
            var iSensorsTry1 = baseList.Cast<IntSensor>();
            //seen on other StackOverflow Posts -- fails
            var iSensorsTry2 = baseList.ConvertAll(instance => (IntSensor)instance);
            //seen on other StackOverflow Posts -- fails
            var iSensorsTry3 = baseList.OfType<IntSensor>();

            model.InternalSensor = iSensorsTry1.ToList();


            return model;
        }
    }

Answer 1

In your GetSensors method, you are creating instances of the base class Sensor. Trying to implicitly cast them to some other derived class is not possible. You should use a generic type parameter in that method and create instances of the actual derived type.

Like so: (notice the where clause and the new constraint of the T parameter)

public static List<T> GetSensors<T>(JToken jToken) where T : Sensor, new()
{
    var sensors = new List<T>();

    try
    {
        foreach (var item in jToken)
        {
            var s = new T();
            s.Label = item["lab"].ToString();
            s.ActualTemp = item["tf"] != null ? item["tf"].ToString() : "";
            s.HighTemp = item["hf"] != null ? item["hf"].ToString() : "";
            s.LowTemp = item["lf"] != null ? item["lf"].ToString() : "";

            sensors.Add(s);
        }
    }
    catch (Exception)
    {
    }            

    return sensors;
}

Now call it like this:

List<IntSensor> iSensors = ParseJsonData.GetSensors<IntSensor>(internalSensorTree);