in questo (vecchio) esempio, il submit avviene sia al click del bottone che alla pressione del tasto Enter posizionandosi nella TextBox:


ASPX
codice:
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <title></title>
    <script type="text/javascript">
        document.getElementById('nome').onkeydown = function (e) {
            if (e.keyCode == 13) {
                forms[0].submit();
            }
        };
    </script>
</head>
<body>
    <form id="form1" runat="server">
        <div>
            Name:
            <input type="text" name="nome" /><br />
            <input type="submit" />
        </div>
    </form>
</body>
</html>

CODEBEHIND:
codice:
protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        ViewState["pb"] = 0;
    }


    Response.Write("num postback: " + ViewState["pb"].ToString());
    ViewState["pb"] = ((int)ViewState["pb"]) + 1;
}