Notification Window

public int iPopUpIndex { get; set; }
public int iPopUpLayer { get; set; }
.
.
.
iOffset = (iPopUpIndex * frmPopup.Size.Height) + (iPopUpIndex * 5);

namespace NotificationWindow
{
    public class PopupNotifierCollection : System.Collections.CollectionBase
    {
        public PopupNotifierCollection(int pi_maxPopUp)
        {
            mi_maxPopUp = pi_maxPopUp;
        }

        private int mi_maxPopUp;
        private Dictionary<int, ArrayList> md_PopUpList = new Dictionary<int, ArrayList>();

        public PopupNotifier this[int index]
        {
            get { return (PopupNotifier)List[index]; }
            set { List[index] = value; }
        }
        
        public int Add(PopupNotifier item)
        {
            item.Close += new System.EventHandler(item_Close);
            int layer = 0;
            int index = 0;
            findNextPopUp(out layer,out index);
            item.PopUpLayer = layer;
            item.PopUpIndex = index;
            return this.List.Add(item);   
        }


        void item_Close(object sender, System.EventArgs e)
        {
            Remove((PopupNotifier)sender);
        }

        public bool Contains(PopupNotifier item)
        {
            return this.List.Contains(item);
        }

        public void Remove(PopupNotifier item)
        {
            removePopUp(item.PopUpLayer, item.PopUpIndex);
            this.List.Remove(item);
        }

        public int IndexOf(PopupNotifier item)
        {
            return this.List.IndexOf(item);
        }

        public void Popup()
        {
            foreach (PopupNotifier item in List)
            {
                //item.Popup(List.IndexOf(item));
                item.Popup();
            }
        }

        private void removePopUp(int layer, int index){
            md_PopUpList[layer].Remove(index);
            if (md_PopUpList[layer].Count == 0)
            {
                md_PopUpList.Remove(layer);
            }
        }

        private void findNextPopUp(out int layer, out int index) {
            layer = 0;
            index = 0;
            int numLayers = md_PopUpList.Count;

            for (int i = 0; i < numLayers; i++ )
            {
                if (md_PopUpList[i].Count >= mi_maxPopUp)
                {
                    layer++;
                    continue;
                }
                else 
                {
                    layer = i;
                    md_PopUpList[i].Sort();
                    int tmpIndex = 0;
                    foreach (int j in md_PopUpList[i])
                    {
                        if (j != tmpIndex)
                        {
                            break;
                        }
                        tmpIndex++;
                    }
                    index = tmpIndex;
                    break;
                }
            }

            addNextPopUp(layer, index);
        }

        private void addNextPopUp(int layer, int index) {
            if (md_PopUpList.ContainsKey(layer))
            {
                md_PopUpList[layer].Add(index);
            }
            else 
            { 
                ArrayList li_counter = new ArrayList();
                li_counter.Add(index);
                md_PopUpList.Add(layer, li_counter);
            }
        }
    }
}

Imports System.ComponentModel
Imports NotificationWindow

Namespace NotificationWindow
    Public Class PopupNotifierCollection
        Inherits System.Collections.CollectionBase
        Public Sub New()
        End Sub

        Default Public Property Item(index As Integer) As PopupNotifier
            Get
                Return DirectCast(List(index), PopupNotifier)
            End Get
            Set(value As PopupNotifier)
                List(index) = value
            End Set
        End Property

        Public Function Add(item As PopupNotifier) As Integer
            Return Me.List.Add(item)
        End Function

        Public Function Contains(item As PopupNotifier) As Boolean
            Return Me.List.Contains(item)
        End Function

        Public Sub Remove(item As PopupNotifier)
            Me.List.Remove(item)
        End Sub

        Public Function IndexOf(item As PopupNotifier) As Integer
            Return Me.List.IndexOf(item)
        End Function

        Public Sub Popup(Optional index As Integer = 0)
            For Each item As PopupNotifier In List
                item.Popup(List.IndexOf(item))
            Next

        End Sub
    End Class
End Namespace

Imports PopupNotifier
Imports NotificationWindow.PopupNotifierCollection
Imports NotificationWindow

Public Class Form1

    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click

        Dim nc As New PopupNotifierCollection()

        Dim pn As New PopupNotifier()

        pn.TitleText = "Title 1"
        pn.ContentText = "Content 1"
        ' pn.AnimationDuration = 1000
        'pn.Delay = 3000
        nc.Add(pn)

        pn = New PopupNotifier()
        pn.TitleText = "Titre 2"
        pn.ContentText = "Content 2"
        nc.Add(pn)

        nc.Popup()

    End Sub
End Class