accessing arraylist of objects inside a class

You need to cast the ArrayList element to its actual type before you can access a property of that type. Try this example:

using System;
using System.Collections;

class Program
{
    static void Main()
    {
        A a = new A();
        ArrayList al = new ArrayList();
        B b = new B();
        b.MyInt = 3;
        al.Add(b);
        a.ListOfB = al;
        Console.WriteLine(((B)a.ListOfB[0]).MyInt.ToString());
        Console.ReadLine();
    }
}

class A
{
   ArrayList listOfB;

   public ArrayList ListOfB
   {
       get{ return listOfB; }
       set{ listOfB = value; }
   } 

}

class B
{
  int myInt;

  public int MyInt
  {
      get{ return myInt; }
      set{ myInt = value; }

  }
 
}