Test if Convert.ChangeType will work between two types

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));

I was just encountering this same issue, and I used Reflector to look at the source for ChangeType. ChangeType throws exceptions in 3 cases:

1. conversionType is null
2. value is null
3. value does not implement IConvertible

After those 3 are checked, it is guaranteed that it can be converted. So you can save a lot of performance and remove the try{}/catch{} block by simply checking those 3 things yourself:

public static bool CanChangeType(object value, Type conversionType)
{
    if (conversionType == null)
    {
        return false;
    }

    if (value == null)
    {              
        return false;
    }

    IConvertible convertible = value as IConvertible;

    if (convertible == null)
    {
        return false;
    }

    return true;
}