The PumaCode.org Blog

While writing a data loading routine in C# with .NET 2.0, I came across an apparent bug which prevented this method from converting a nullable type. A bit of Googling turned up a post by my brother Peter about this issue and a possible workaround.

I took his solution a step further and basically wrote my own ChangeType method which properly handles nullable types. I then got in touch with Peter about my solution and he suggested a better way of detecting the nullable type (I was just using a regex at first). Anyway, the end result is listed below.

In case you’re wondering why I check for a null value only after I determine that conversionType is nullable, it’s because I want the final Convert.ChangeType to throw the exception when conversionType can’t accept a null value, rather than causing the exception to be thrown in the caller.

public object ChangeType(object value, Type conversionType)
{
    if ( conversionType.IsGenericType &&
        conversionType.GetGenericTypeDefinition( ).Equals( typeof( Nullable<> ) ) ) {
 
        if(value == null)
            return null;
 
        System.ComponentModel.NullableConverter nullableConverter
            = new System.ComponentModel.NullableConverter(conversionType);
 
        conversionType = nullableConverter.UnderlyingType;
    }
 
    return Convert.ChangeType(value, conversionType);
}