[Berenger] ClassWindow.cs

using UnityEngine;
using UnityEditor;
using System.Collections.Generic;

public class ClassWindow : EditorWindow
{
    private static ClassWindow window;
    public List< ClassA > list;

    [MenuItem ("My Window/Class")]
    static void Init ()
    {
        window = EditorWindow.GetWindow (typeof (ClassWindow)) as ClassWindow;
        Debug.Log("Init");
    }

    private void OnGUI()
    {
        if( list == null )
            list = new List<ClassA>();

        if( GUI.Button( new Rect( 10, 10, 100, 100 ), "Add Class A" ) )
            list.Add( new ClassA() );

        if( GUI.Button( new Rect( 110, 10, 100, 100 ), "Add Class B" ) )
            list.Add( new ClassB() );

        // Once you compile again, this is going to display only 'AAAAAAAAA'
        GUILayout.BeginArea( new Rect( 10, 110, 200, 200 ) );
            GUILayout.Space(20);
            GUILayout.Label( "Childcount : " + list.Count );
            GUILayout.Space(20);
            foreach( ClassA a in list )
                a.Draw();
        GUILayout.EndArea();
    }
}