Triggering a postback from Javascript fails

I am trying to trigger a postback if a certain condition is true. Initially, a user will click on a button on my form, the server does some work, and in the process of doing that work it assigns a hidden field the value of '1'. When the page reloads after that very first postback, I am trying to use javascript to check the hidden field, and if it is '1' I need the page to postback again so the server side can do some additional processing. The reason for doing it this roundabout way is so that 开发者_JS百科I can create controls on the form from my C# code behind as well as download a file in 1 user interaction. Here is what I have so far:

<script type="text/javascript" language="JavaScript">
        function atload() {
            var HWInfo = document.getElementById('HiddenHW').value;
            if (HWInfo == '1') {
                alert("flag has been set");

                __doPostBack('<%= hdnHidden.UniqueID  %>', '');
             }

        }
        $(document).ready(atload);

    </script>

The alert that says the flag has been set correctly fires, but the __doPostBack does not. In my ASPX file, here is the relevant part:

 <form id="InventoryForm" runat="server">

<div>
    <asp:Label ID="lblClientList" runat="server" Text="Client List"></asp:Label>
    <asp:DropDownList ID="comboClientList" runat="server"></asp:DropDownList>
    <asp:Label ID="spacer1" runat="server" Text="     "></asp:Label>
    <asp:Button ID="btnGenerateHWReport" runat="server" Text="Generate Hardware Inventory Report" />
    <asp:Label ID="spacer2" runat="server" Text="     "></asp:Label>
    <asp:Button ID="btnGenerateSWReport" runat="server" Text="Generate Software Inventory Report" />
    <br />
    <br />

    <asp:Panel ID="MissingCompPanel" runat="server"></asp:Panel>
    <asp:HiddenField ID="HiddenHW" runat="server" Value="0" />
    <asp:HiddenField ID="hdnHidden" runat="server" />

</div>
</form>

I can tell the postback never fires, because I have breakpoints in the Page_Load C# codebehind that never get tripped. I have break points on almost every single line of this:

        if (!Page.IsPostBack)
        {
            // Page is not a postback, this is the first visit here
            string foo = HiddenHW.Value;
        }
        else
        {
            // Page is a postback and not initial load
            string foo = HiddenHW.Value;
        }

Why is my __doPostBak after the alert not firing, and is there a better way to do this? The end result I want is if my hidden field is '1', then I want my 2nd trip to the server to 1) actually happen and 2) know that the hidden field is '1' and not its default '0'.

Thanks!

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how about just clicking the submit button programatically and have it call __doPostBack the way it normally does?

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Try invoking the __doPostBack method on the page instead of the hidden control

__doPostBack('__Page', '');

---

When you get the value of HiddenHW, you're not using the right ID. If you look at the rendered source, the ID of the control is something like ctl00_HiddenHW. To get that ID, you should use HiddenHW.ClientID. I believe __doPostBack also needs the ClientID, not UniqueID.

function atload() {
    var HWInfo = document.getElementById('<%= HiddenHW.ClientID %>').value;
    if (HWInfo == '1') {
        alert("flag has been set");

        __doPostBack('<%= hdnHidden.ClientID %>', '');
    }
}