Copy a Nullable property to a non-Nullable version

问题:

I am writing code to transform one object to another using reflection...

It's in progress but I think it would boil down to the following where we trust both properties have the same type:

    private void CopyPropertyValue(object source, string sourcePropertyName, object target, string targetPropertyName)
    {
        PropertyInfo sourceProperty = source.GetType().GetProperty(sourcePropertyName);
        PropertyInfo targetProperty = target.GetType().GetProperty(targetPropertyName);
        targetProperty.SetValue(target, sourceProperty.GetValue(source));
    }

However I have the additional issue that the source type might be Nullable and the target type not. e.g Nullable<int> => int. In this case I need to make sure it still works and some sensible behaviour is performed e.g. NOP or set the default value for that type.

What might this look like?

回答1:

Given that GetValue returns a boxed representation, which will be a null reference for a null value of the nullable type, it's easy to detect and then handle however you want:

private void CopyPropertyValue(
    object source,
    string sourcePropertyName,
    object target,
    string targetPropertyName)
{
    PropertyInfo sourceProperty = source.GetType().GetProperty(sourcePropertyName);
    PropertyInfo targetProperty = target.GetType().GetProperty(targetPropertyName);
    object value = sourceProperty.GetValue(source);
    if (value == null && 
        targetProperty.PropertyType.IsValueType &&
        Nullable.GetUnderlyingType(targetProperty.PropertyType) == null)
    {
        // Okay, trying to copy a null value into a non-nullable type.
        // Do whatever you want here
    }
    else
    {
        targetProperty.SetValue(target, value);
    }
}