Invalid cast from 'System.Int32' to 'System.Nullable`1[[System.Int32, mscorlib]]

Question

Type t = typeof(int?); //will get this dynamically
object val = 5; //will get this dynamically
object nVal = Convert.ChangeType(val, t);//getting exception here
         


        

Answer 1

You have to use Nullable.GetUnderlyingType to get underlying type of Nullable.

This is the method I use to overcome limitation of ChangeType for Nullable

public static T ChangeType(object value) 
{
   var t = typeof(T);

   if (t.IsGenericType && t.GetGenericTypeDefinition().Equals(typeof(Nullable<>))) 
   {
       if (value == null) 
       { 
           return default(T); 
       }

       t = Nullable.GetUnderlyingType(t);
   }

   return (T)Convert.ChangeType(value, t);
}

non generic method:

public static object ChangeType(object value, Type conversion) 
{
   var t = conversion;

   if (t.IsGenericType && t.GetGenericTypeDefinition().Equals(typeof(Nullable<>))) 
   {
       if (value == null) 
       { 
           return null; 
       }

       t = Nullable.GetUnderlyingType(t);
   }

   return Convert.ChangeType(value, t);
}