GridView模版列中取控件的值

//以下事件用於checkbox控件更動時取控件的值 

protected void CheckBox2_CheckedChanged(object sender, EventArgs e)
    {

        //以下兩行若不寫,則會出現沒有實例化錯誤
        CheckBox cb = new CheckBox();
        Label lb = new Label();

        for (int i = 0; i < gv.Rows.Count; i++)
        {
            cb = (CheckBox)gv_BomInfo.Rows[i].FindControl("CheckBox2");
            lb = (Label)gv_BomInfo.Rows[i].FindControl("Label4");

            int  lb_txt = Convert.ToInt32(lb.Text.ToString());          

            if (cb.Checked == true)
            {

                 /**/
            }
            else
            {

                /**/

            }
        }