change div display with change checked of checkbox in bindec gridview using asp.net

i have gridviewthat binded to database. there is checkbox in it that i want change display attribute of another div with checkbox checked value. this is my backend code in asp.net, but it isn't work! what can i do to solve it? thanks!

protected void gv_sourceGalleryPic_RowCommand(object sender, GridViewCommandEventArgs e)
    {
        if (e.CommandName == "checkPic")
        {
            CheckBox chkItem = (CheckBox)gv_sourceGalleryPic.FindControl("ck_checkGalleryPic_copyMove");

            if (chkItem.Checked == true)
            {
                div1.Style.Add(HtmlTextWriterStyle.Display, "block");
            }
        }
    }