C＃如何从父级列表访问继承的对象

Question

I'm trying to find a way to make a list of parent object with a variety of inherited objects. Here is an example.

class Prog {
    public Prog ( ) {
        List<Shape> shapes = new List<Shape>();
        shapes.Add( new Cube() );
        shapes.Add( new Shape() );

        //All those ways will not work, I cannot figure a way how to do this
        shapes[0].CubeFunction(); 
        (Cube)shapes[0].CubeFunction();
        Cube cube = shapes[0];
    }
}

class Shape {
    public Shape (){}
}

class Cube : Shape {        
    public Cube (){}
    public void CubeFunction(){}
}

Does anyone know how to get the code in class Prog to work?

Answer 1

Your cast version is nearly right - it's only wrong because of precedence. You'd need:

((Cube)shapes[0]).CubeFunction();

Alternatively:

Cube cube = (Cube) shapes[0];
cube.CubeFunction();

The need to cast like this is generally a bit of a design smell, mind you - if you can avoid it, it's worth trying to do so.

Answer 2

If you are not sure the cast is valid and don't want an InvalidCastException to be thrown, you can do like this:

Cube cube = shapes[0] as Cube;
if (cube == null)
{
    // cast is not valid
}
else
{
    cube.CubeFunction();
}