delegate event not returning

public partial class Control_WebUserControl : System.Web.UI.UserControl
{
PageChangedEventHandler PageChanged ;//geting null here

public delegate void PageChangedEventHandler(object sender, CustomPageChangeArgs e);

public virtual void OnPageChanged(CustomPageChangeArgs e)
{
// If an event has no subscribers registerd, it will
// evaluate to null. The test checks that the value is not
// null, ensuring that there are subsribers before
// calling the event itself.

if (PageChanged != null)
{
//point the refrence to PageChanged Method
PageChanged(this, e);
}
}

void Pager_PageChanged(object sender, CustomPageChangeArgs e)
{
if (PageChanged != null)
PageChanged(sender, e);
//throw new Exception("The method or operation is not implemented.");
}

protected void ddlPageNumber_SelectedIndexChanged(object sender, EventArgs e)
{
CustomPageChangeArgs args = new CustomPageChangeArgs();
args.CurrentPageSize = Convert.ToInt32(this.ddlPageSize.SelectedItem.Value);
args.CurrentPageNumber = Convert.ToInt32(this.ddlPageNumber.SelectedItem.Text);
args.TotalPages = Convert.ToInt32(this.lblTotalNumberOfPages.Text);
Pager_PageChanged(this, args);

lblTotalNumberOfPages.Text = string.Format(" {0} ", args.TotalPages.ToString());
}

in desgin page

<asp:DropDownList ID="ddlPageNumber" runat="server" CssClass="DropDown" AutoPostBack="true"
OnSelectedIndexChanged="ddlPageNumber_SelectedIndexChanged">


please check comment where i getting error