Web Forms :: Add Usercontrol With Variable Button Events

I have the problem that when i´m adding my usercontrol to my default page the events do not fire. I already know that I had to add the usercontrol as soon as possible to the lifecycle, but I can´t because I know the number of buttons after clicking on my default button.

code:

my default.aspx.cs page
protected override void OnInit(EventArgs e)
{
if (!IsPostBack)
{
addPruefstation aP = (addPruefstation)this.LoadControl("addPruefstation.ascx");
aP.ID = "ucPruefstation";
Session["ucPruefstation"] = aP;
}
base.OnInit(e);
}
protected void bApply_Click(object sender, ImageClickEventArgs e)
{
int anz;
Int32.TryParse(((TextBox)tablePruefstand.FindControl("tbPruefstandstationen")).Text, out anz); //here i´m getting the number of buttons
Session["anzStation"]=anz;
addPruefstation aP = (addPruefstation)Session["ucPruefstation"];
aP.anz = anz;
Session["ucPruefstation"] = aP;
phPruefstation.Controls.Add(aP);
}
my usercontrol.acsx.cs:
public int anz;
protected override void OnInit(EventArgs e)
{
for (int i = 0; i < anz; i++)
{
tcButton=new TableCell();
trPruefstation = new TableRow();
tcEmpty = new TableCell();
tcLabel = new TableCell();
tcTextbox = new TableCell();
tcLabel.Controls.Add(new LiteralControl("Anzahl Leaks"));
tcTextbox.Controls.Add(new TextBox() { ID = "Leak" + i, Text = "0", AutoPostBack = false });
ImageButton imgButton = new ImageButton() { ID = "" + i, ImageUrl = "~/Img/1rightarrow-256.png", Height=15};
imgButton.Click += new ImageClickEventHandler(imgButton_Click);
tcButton.Controls.Add(imgButton);
trPruefstation.Cells.Add(tcEmpty);
trPruefstation.Cells.Add(tcLabel);
trPruefstation.Cells.Add(tcTextbox);
trPruefstation.Cells.Add(tcButton);
tablePruefstation.Rows.Add(trPruefstation);
}
base.OnInit(e);
}
void imgButton_Click(object sender, ImageClickEventArgs e) //this event never be fired
{
throw new NotImplementedException();
}