I'm guessing I am just doing something wrong, because I don't see how it is possible for .NET to not include this feature. I have a base abstract class, Shape, with many different inherited Shape Types. All Shape Types inherit from the base abstract class, Shape, and are all (including Shape) located under the Shapes namespace.
"value" is a type parameter which is passed into a method. Say for example, value is of type "Shapes.ExtrudedCircle" The following if statement doesn't work as I expected:
if (value == typeof(Shapes.Shape))
{
Shape
so = (Shape)value; // Doesn't go into this if statement:(
return
so;
}
However, this will:
if (value == typeof(Shapes.ExtrudedCircle))
{
Shape
so = (Shape)value; // Success, but is not what I need:(
return
so;
}
Any ideas what I'm doing wrong Shouldn't .NET understand that ExtrudedCircle is still of the Shape Type
Finding Base Types dynamically
Inaki Ayucar
domw001
You are doing type equality rather than equivalence. What you want to be able to do is determine if some type is either a specific type or derived from it. You can't use == for that. Instead, since you have the type, you should use the IsSubclassOf method.
public
class Shape {}public class Circle : Shape {}
public class Triangle : Shape {}
public class Rectangle : Shape {}
class Program
{
static void PrintShape ( Type type )
{
if (type.IsSubclassOf(typeof(Shape)) || (type == typeof(Shape)))
Console.WriteLine("Is a shape");
if (type.IsSubclassOf(typeof(Circle)) || (type == typeof(Circle)))
Console.WriteLine("Is a circle");
if (type.IsSubclassOf(typeof(Triangle)) || (type == typeof(Triangle)))
Console.WriteLine("Is a Triangle");
if (type.IsSubclassOf(typeof(Rectangle)) || (type == typeof(Rectangle)))
Console.WriteLine("Is a Rectangle");
}
static void PrintShape ( Shape shape )
{
if (shape is Shape)
Console.WriteLine("Is a shape");
if (shape is Circle)
Console.WriteLine("Is a circle");
if (shape is Triangle)
Console.WriteLine("Is a Triangle");
if (shape is Rectangle)
Console.WriteLine("Is a Rectangle");
}
static void Main ( string[] args )
{
Rectangle rect = new Rectangle();
PrintShape(rect.GetType());
}
}
For comparison the second version of PrintShape doesn't use the type at all but rather uses the is operator to distinguish. It is the superior method to use when possible rather than dealing with types directly.
Michael Taylor - 8/2/06