Set property Nullable<> by reflection

Question

I try to set a Nullable<> property dynamicly.

I Get my property ex :

PropertyInfo property = class.GetProperty("PropertyName"); // My property is Nullable<> at this time So the type could be a string or int

I want to set my property by reflection like

property.SetValue(class,"1256",null);

It's not working when my property is a Nullable<> Generic. So i try to find a way to set my property.

To know the type of my nullable<> property i execute

Nullable.GetUnderlyingType(property.PropertyType)

Any idea ?

• I Try to create an instance of my Nullable<> property with

  var nullVar = Activator.CreateInstance(typeof(Nullable<>).MakeGenericType(new Type[] { Nullable.GetUnderlyingType(property.PropertyType) }));

But nullVar is always Null

Answer 1

I hit this same problem as well as an issue with Convert.ChangeType not handling DateTimes on Nullables so I combined a couple of stackoverflow solutions with some .NET 4 dynamic magic to get something I think is kind of sweet. If you look at the code, we use dynamic to type the object to Nullable at run time, then the run time treats it differently and allows assignments of the base type to the nullable object.

public void GenericMapField(object targetObj, string fieldName, object fieldValue)
{
    PropertyInfo prop = targetObj.GetType().GetProperty(fieldName);
    if (prop != null)
    {
        if (prop.PropertyType.IsGenericType && prop.PropertyType.GetGenericTypeDefinition() == typeof(Nullable<>))
        {
            dynamic objValue = System.Activator.CreateInstance(prop.PropertyType);
            objValue = fieldValue;
            prop.SetValue(targetObj, (object)objValue, null);
        }
        else
        {
            prop.SetValue(targetObj, fieldValue, null);
        }
    }
}

Answer 2

public static void SetValue(object target, string propertyName, object value)
{
  if (target == null)
    return;

  PropertyInfo propertyInfo = target.GetType().GetProperty(propertyName);

  object convertedValue = value;
  if (value != null && value.GetType() != propertyInfo.PropertyType)
  {
    Type propertyType = Nullable.GetUnderlyingType(propertyInfo.PropertyType) ?? propertyInfo.PropertyType;
    convertedValue = Convert.ChangeType(value, propertyType);
  }

  propertyInfo.SetValue(target, convertedValue, null);
}