MAC地址值显示为null

Question

我正在使用以下javascript代码在我的母版页中获取MAC地址。在master.cs页面后面的代码中，在Page_Load（）方法中我写了“string mac = inpHide.Value.ToString（）;”得到那个mac地址。但是当我调试时，我只获得null值。我需要在global.asax中使用该值。有什么帮助吗？

 <script type="text/javascript">
    function MACAddress() {
        var locator = new ActiveXObject("WbemScripting.SWbemLocator");
        var service = locator.ConnectServer(".");
        var properties = service.ExecQuery("SELECT * FROM Win32_NetworkAdapterConfiguration");
        var e = new Enumerator(properties);
        var MACaddress = '';
        for (; !e.atEnd(); e.moveNext()) {
            var p = e.item();
            if (p.MACAddress) {
                MACaddress = MACaddress + p.MACAddress + ',';
            }
        }
        MACaddress = MACaddress.substring(0, MACaddress.length - 1);
        var hiddenControl = '<%= inpHide.ClientID %>';
        document.getElementById(hiddenControl).value = MACaddress;        
    }
</script>

在我的母版页中：

<div><input id="inpHide" type="hidden" runat="server"/></div>