Accessing value of a hidden field on Masterpage from codebehind

In a follow up to my previous question, I want to get the value of the hidden input field from the child page codebehind.

I tried HtmlInputHidden hdnID = (HtmlInputHidden)Page.Master.FindControl("ctl00_hdnField"); but I get a "null" value.

A snippet of the Masterpage is:

<head runat="server">
    <title>
        <asp:ContentPlaceHolder ID="TitleContent" runat="server"></asp:ContentPlaceHolder>
        <asp:Literal ID="Literal2" runat="server" Text=" : Logistics Management" />
    </title>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />

    <link href="~/css/styles.css" rel="stylesheet" type="text/css" />

    <asp:ContentPlaceHolder ID="ScriptCssContent" runat="server">
    </asp:ContentPlaceHolder>

</head>
<body>

<form id="form1" runat="server">
    ......
    ......
    ......
        <div id="container">
        ....
        ....
        ....
                <div id="content" style="z-index:0;">
                <asp:HiddenField ID="hdnField" runat="server" Value=""/>
                ....
                ....
                ....
                        <asp:ContentPlaceHolder ID="MainContent" runat="server">

                        </asp:ContentPlaceHolder>
            </div>
        </div>
</form>

On my Child aspx page, I have this javascript block:

window.onload = function() {
    var newDate = new Date();
    var hidField = document.getElementById("ctl00_hdnField");

    if (hidField != null)
        hidField.value = newDate.toLocaleString();
}

When I "Add Watch" to

document.getElementById("ctl00_hdnField")

the value is correct.

Question: How would I access the value inside hdnField control, from codebehind?

So change it FROM

HtmlInputHidden hdnID = (HtmlInputHidden)Page.Master.FindControl("ctl00_hdnField");

HiddenField hdnID = (HiddenField)Page.Master.FindControl("hdnField");

It's just a casting thing - notice HtmlInputHidden changed to HiddenField. You also don't need the ct100_ part - this is just so the HTML rendered element has a unique ID.

The control on your page is an asp.net control, not a generic HTML control.

You would use HtmlInputHidden if you put a generic <input type="hidden" /> in your HTML.

You should create a property in Masterpage which wrap the HiddenField.

public String HdnFieldValue
{
get
{
    return hidField.Value;
}
set
{
    hidField.Value = value;
}
}

And in page code behind you can access it like this:

((YourCustomMaster)Page.Master).HdnFieldValue

If something is not clear please ask me.

I don't think you need to prefix the hidden field's ID with ctl00_, just use the normal ID:

(HtmlInputHidden)Page.Master.FindControl("hdnField");

Use something like:

if (Page.Master.FindControl("hdnField") != null)
{
    String myValue = (HtmlInputHidden)Page.Master.FindControl("hdnField").value;
}

来源：https://stackoverflow.com/questions/15689859/accessing-value-of-a-hidden-field-on-masterpage-from-codebehind

标签

ASP.NET

master-pages

hidden-field