Type Data From InvalidCastException

Question

The question is pretty simple: is there any way to get the problematic System.Types from an InvalidCastException? I want to be able to display information about the failed type casting in a format such as "Expected {to-type}; found {from-type}", but I cannot find a way to access the types that were involved.

EDIT: The reason I need to be able to access the types that were involved is because I have information about shorter names for some times. For example, instead of the type RFSmallInt, I want to say that the type is actually smallint. Instead of an error message

Unable to cast object of type 'ReFactor.RFSmallInt' to type 'ReFactor.RFBigInt'.

I actually want to display

Expected bigint; recieved smallint.

Answer 1

One solution could be to implement a Cast function which gives you that information if the cast doesn't succeed:

static void Main(string[] args)
{
    try
    {
        string a = Cast<string>(1);
    }
    catch (InvalidCastExceptionEx ex)
    {
        Console.WriteLine("Failed to convert from {0} to {1}.", ex.FromType, ex.ToType);
    }
}



public class InvalidCastExceptionEx : InvalidCastException
{
    public Type FromType { get; private set; }
    public Type ToType { get; private set; }

    public InvalidCastExceptionEx(Type fromType, Type toType)
    {
        FromType = fromType;
        ToType = toType;
    }
}

static ToType Cast<ToType>(object value)
{
    try
    {
        return (ToType)value;
    }
    catch (InvalidCastException)
    {
        throw new InvalidCastExceptionEx(value.GetType(), typeof(ToType));
    }
}

Answer 2

I've done this kind of thing with a custom exception:

public class TypeNotImplementedException : Exception {

    public Type ToType { get { return _ToType; } }
    private readonly Type _ToType;

    public Type FromType { get { return _FromType; } }
    private readonly Type _FromType;

    public override System.Collections.IDictionary Data {
        get {
            var data = base.Data ?? new Hashtable();
            data["ToType"] = ToType;
            data["FromType"] = FromType;
            return data;
        }
    }

    public TypeNotImplementedException(Type toType, Type fromType, Exception innerException) 
        : base("Put whatever message you want here.", innerException) {
        _ToType = toType;
        _FromType = fromType;
    }

}

class Program {

    private static T Cast<T>(object obj) {
        try {
            return (T)obj;
        }
        catch (InvalidCastException ex) {
            throw new TypeNotImplementedException(typeof(T), obj.GetType(), ex);
        }
    }

    static void Main(string[] args) {

        try {
            Cast<string>("hello world" as object);
            Cast<string>(new object());
        }
        catch (TypeNotImplementedException ex) {
            Console.WriteLine(ex);
        }
    }
}