Cast to a type from a generic class

Question

I have a generic class that looks like this:

public interface IStationProperty
   {
      int Id { get; set; }
      string Desc { get; set; }
      object Value { get; }
      Type ValueType { get; }
   }

   [Serializable]
   public class StationProp<T> : IStationProperty
   {
      public StationProp()
      {
      }

      public StationProp(int id, T val, string desc = "")
      {
         Id = id;
         Desc = desc;
         Value = val;
      }

      public int Id { get; set; }
      public string Desc { get; set; }
      public T Value { get; set; }

      object IStationProperty.Value
      {
         get { return Value; }
      }

      public Type ValueType
      {
         get { return typeof(T); }
      }

The property that gets the type is:

public Type ValueType
      {
         get { return typeof(T); }
      }

So in my code, I have a loop pulling values (as string) from the db, here I want to do a type conversion (on the left side) so I can do a reliable value comparison.

I would like something like this:

var correctlyTypedVariable = (prop.ValueType) prop.Value;

I know this kind of thing has to be possible.

If you can explain what you're planning to do with `correctlyTypedVariable` it will be easy to answer. Some explanation or pseudo code? — Sriram Sakthivel, Jan 29 '15 at 10:17
Could this be the solution? http://stackoverflow.com/questions/972636/casting-a-variable-using-a-type-variable So e.g. `var correctlyTypedVariable = Convert.ChangeType(prop.Value, prop.ValueType);` — Zdeněk Jelínek, Jan 29 '15 at 10:17
cant do that. if you are using var the type must be clear at compile time not runtime. you can only do something like: "if(yourobject is StationProp)" etc. — Florian Schmidinger, Jan 29 '15 at 10:18
[See if this helps](http://stackoverflow.com/questions/27972266/compare-numeric-types-when-types-are-unknown/27972408#27972408) — Sriram Sakthivel, Jan 29 '15 at 10:22
if there are few and only the comparing is the problem i would implement ICompareable and check/cast the types there. — Florian Schmidinger, Jan 29 '15 at 10:32
You want to do a value comparison with what exactly? Is it an equality check or an ordering comparison? — Jon, Jan 29 '15 at 10:43

score 2 · Accepted Answer · answered Jan 29 '15 at 10:26

You already have

public T Value { get; set; }

which returns the typed value. If on the following code, the prop object is of type IStationProperty

var correctlyTypedVariable = (prop.ValueType) prop.Value;

then maybe your problem is on the interface : you should better use a generic one :

public interface IStationProperty
{
  int Id { get; set; }
  string Desc { get; set; } 
  Type ValueType { get; }
}

public interface IStationProperty<T> : IStationProperty
{ 
   T Value { get; } 
}

Florian Schmidinger · Answer 2 · 2015-01-29T15:01:08.377

With IComparable:

public interface IStationProperty : IComparable<IStationProperty>
{
    int Id { get; set; }
    string Desc { get; set; }
    object Value { get; }
    Type ValueType { get; }
}

[Serializable]
public class StationProp<T> : IStationProperty where T : IComparable
{
    public StationProp()
    {
    }

    public StationProp(int id, T val, string desc = "")
    {
        Id = id;
        Desc = desc;
        Value = val;
    }

    public int Id { get; set; }
    public string Desc { get; set; }
    public T Value { get; set; }

    object IStationProperty.Value
    {
        get { return Value; }
    }

    public Type ValueType
    {
        get { return typeof(T); }
    }

    public int CompareTo(IStationProperty other)
    {
        if (other.ValueType == typeof(string))
        {
            return Value.CompareTo((string)other.Value);
        }
        else if (other.ValueType == typeof(int))
        {
            return Value.CompareTo((int)other.Value);
        }
        else if (other.ValueType == typeof(double))
        {
            return Value.CompareTo((double)other.Value);
        }
        throw new NotSupportedException();
    }
}

Cast to a type from a generic class

2 Answers2