How to get custom control's dropdown index changed event in page?

Question

I'm creating a custom control where I'm extending the GridView class for custom paging. I attached a ropdown in the GridView OnRowCreated event and set the autopostback property of the dropdown to true. Now I want to handle this index changed event of tje dropdown on the page where I'm using this custom control. I tried using Delegate and event but I got event null in dropdown index changed event.

public delegate void Chnageme(int inData);
public event Chnageme onChnageDropDown;

protected override void OnRowCreated(GridViewRowEventArgs e)
    {
        if (this.AllowPaging == true)
        {

            if (e.Row.RowType == DataControlRowType.Pager)
            {
                DropDownList ddlPage = new DropDownList();
                ddlPage.Items.Add(new ListItem("10", "10"));
                ddlPage.Items.Add(new ListItem("100", "100"));
                ddlPage.AutoPostBack = true;
                ddlPage.SelectedIndexChanged += new EventHandler(ddlPage_SelectedIndexChanged);

                TableCell cellLeft = new TableCell();
                cellLeft.HorizontalAlign = HorizontalAlign.Left;
                cellLeft.Controls.Add(ddlPage);
           }
       }
   }

void ddlPage_SelectedIndexChanged(object sender, EventArgs e)
    {
          //Found null
        onChnageDropDown(Convert.ToInt32(((DropDownList)sender).SelectedValue));
    }