Test if Convert.ChangeType will work between two types

Question

This is a follow-up to this question about converting values with reflection. Converting an object of a certain type to another type can be done like this:

object convertedValue = Convert.ChangeType(value, targetType);

Given two Type instances (say FromType and ToType), is there a way to test whether the conversion will succeed?

E.g. can I write an extension method like this:

public static class TypeExtensions
{
    public static bool CanChangeType(this Type fromType, Type toType)
    {
        // what to put here?
    }
}

EDIT: This is what I have right now. Ugly, but I don't see another way yet...

bool CanChangeType(Type sourceType, Type targetType)
{
  try
  {
    var instanceOfSourceType = Activator.CreateInstance(sourceType);
    Convert.ChangeType(instanceOfSourceType, targetType);
    return true; // OK, it can be converted
  }
  catch (Exception ex)
  {
    return false;
  }

Answer 1

Checking the method Convert.ChangeType in reflector I found this in the static constructor:

ConvertTypes = new Type[] { 
        typeof(Empty), typeof(object), typeof(DBNull), typeof(bool), typeof(char), typeof(sbyte), typeof(byte), typeof(short), typeof(ushort), typeof(int), typeof(uint), typeof(long), typeof(ulong), typeof(float), typeof(double), typeof(decimal), 
        typeof(DateTime), typeof(object), typeof(string)
     };

In the end, this method is just checking either if the source is implementing IConvertible or if the target is one of the ConvertTypes above. So your method should look something like this (very rough):

return (ConvertTypes.Contains(toType) || typeof(IConvertible).IsAssignableFrom(fromType));

Answer 2

I have written a little framework that includes a Convert class that can do more than the System.Convert class. If you are interested in using it, you can download it from my website. It doesn't have the ability to determine if you can convert between values, but that seems like a good feature to add.

It does include the ability to convert values based on:

• IConvertible
• TypeConverters
• ToXxx methods
• Parse static methods
• Parameterized constructor
• and a few other minor ones

BizArk Feature Spotlight – Data Type Conversions

Answer 3

There seems to be no way provided out of the box. The code snippet I already posted in my edited question does the trick in my case:

bool CanChangeType(Type sourceType, Type targetType)
{
try
{
   var instanceOfSourceType = Activator.CreateInstance(sourceType);
   Convert.ChangeType(instanceOfSourceType, targetType);
   return true; // OK, it can be converted
 }
 catch (Exception ex)
 {
    return false;
 }

The BizArk framework from bbrewder is cool, but (a) does not have this feature yet and (b) is a bit overkill for me right now to extend.