Accessing a property of derived class from the base class in C#

Question

In C#, what is the best way to access a property of the derived class when the generic list contains just the base class.

public class ClassA : BaseClass
{
          


        

Answer 1

If you are doing this a lot, another option would be to create an extension method on the list to give you back the correctly typed enumeration. i.e.

  public static class MyBaseListExtensions
  {
    public static IEnumerable GetAllAs(this List list)
    {
      foreach (var obj in list)
      {
        if (obj is ClassA)
        {
          yield return (ClassA)obj;
        }
      }
    }

    public static IEnumerable GetAllbs(this List list)
    {
      foreach (var obj in list)
      {
        if (obj is ClassB)
        {
          yield return (ClassB)obj;
        }
      }
    }
  }

Then you could use it like....

private void button1_Click(object sender, EventArgs e)
{
  ClassA a1 = new ClassA() { PropertyA = "Tim" };
  ClassA a2 = new ClassA() { PropertyA = "Pip" };
  ClassB b1 = new ClassB() { PropertyB = "Alex" };
  ClassB b2 = new ClassB() { PropertyB = "Rachel" };

  List list = new List();
  list.Add(a1);
  list.Add(a2);
  list.Add(b1);
  list.Add(b2);

  foreach (var a in list.GetAllAs())
  {
    listBox1.Items.Add(a.PropertyA);
  }

  foreach (var b in list.GetAllbs())
  {
    listBox2.Items.Add(b.PropertyB);
  }
}