Accessing hidden-input values edited by JavaScript

Question

I have dynamically created hidden input controls in a C# code-behind file, and then populated their values with JavaScript. I now want to access these variables in C#.

Firebug shows that the values do change with JavaScript, but I'm getting the original values back in the code behind. Any insight would be much appreciated.

JavaScript:

function injectVariables(){
    var hidden = document.getElementById("point1");
    hidden.value = 55;
    var hidden2 = document.getElementById("point2");
    hidden2.value = 55;
    var hidden3 = document.getElementById("point3");
    hidden3.value = 55;
    alert("values changed");
}

ASPX:

<asp:Button OnClick="Update_PlanRisks" OnClientClick="injectVariables()" Text="updatePlanRisks" runat="server" />

C#:

protected override void CreateChildControls()
{
    base.CreateChildControls();
    int planId = Convert.ToInt32(Request.QueryString.Get("plan"));
    planRisks = wsAccess.GetPlanRiskByPlanId(planId);

    foreach (PlanRisk pr in planRisks)
    {
        HtmlInputHidden hiddenField = new HtmlInputHidden();
        hiddenField.ID= "point" + pr.Id;
        hiddenField.Name = "point" + pr.Id;
        hiddenField.Value = Convert.ToString(pr.Severity);
        this.Controls.Add(hiddenField);
    }   
}

protected void Update_PlanRisks(object sender, EventArgs e)
{
    foreach (PlanRisk pr in planRisks)
    {
        int planRiskId = pr.Id;
        string planRiskName = "point" + pr.Id;
        HtmlInputHidden hiddenControl = (HtmlInputHidden) FindControl(planRiskName);
        string val = hiddenControl.Value;
    }
}

Josh Stodola · Accepted Answer · 2009-07-21 17:21:08Z

2

This is one way to get the value from the request...

string point1 = Request.Form["point1"];

answered Jul 21, 2009 at 17:21

Josh Stodola

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Comments

Rex M · Accepted Answer · 2009-07-21 16:28:01Z

0

In CreateChildControls you are explicitly setting the value of the hidden field(s). CreateChildControls runs each time during the page lifecycle (potentially multiple times), when you click submit, the page posts back and runs through the entire lifecycle again - including CreateChildControls - before running the click handler Update_PlanRisks.

The simplest way to avoid this problem is to check if you are in PostBack before setting the value of your hidden fields:

if(!IsPostBack)
{
    hiddenField.Value = Convert.ToString(pr.Severity);
}

edited Jul 21, 2009 at 16:28

answered Jul 21, 2009 at 16:00

Rex M

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1 Comment

ErnieStings Over a year ago

when i add the (!IsPostBack){} my string val = "". how would i get this to access the injected javascript value?

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