How to insert hidden input HTML tags into an ASP.NET page so that the ID or name attributes are not rewritten

Introduction

Recently, I was tasked with interfacing with a payment gateway that required I post information via hidden input fields. I ran into problems, specifically with ASP.NET rewriting the names of my input IDs causing the gateway to ignore them. I tried several different approaches to solve this, but since I am using masterpages, nothing seemed to work.

Solution 1

My solution was to create a custom control. I included properties for “name”, “id”, and “value”. Simply, all this control will do is write out “<input type="hidden" name="" id="" value="" />” with the values for each property.

Here is the code for the control:

using System;
using System.ComponentModel;
using System.Text;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace WebCustomControls.HiddenField
{
    [DefaultProperty("Value")]
    [ToolboxData("<{0}:hiddenField runat="server"></{0}:hiddenField>")]
    public class hiddenField : WebControl
    {    

        [Bindable(false)]
        [Category("Appearance")]
        [DefaultValue("")]
        [Localizable(true)]
        public string Value
        {
            get
            {
                var s = (String)ViewState["Value"];
                return (s ?? String.Empty);
            }
            set
            {
                ViewState["Value"] = value;
            }

        }    

        [Bindable(false)]
        [Category("Appearance")]
        [DefaultValue("")]
        [Localizable(true)]
        public override string ID
        {
            get
            {
                var s = (String)ViewState["ID"];
                return (s ?? String.Empty);
            }
            set
            {
                ViewState["ID"] = value;
            }
        }

        [Bindable(false)]
        [Category("Appearance")]
        [DefaultValue("")]
        [Localizable(true)]
        public string Name
        {
            get
            {
                var s = (String)ViewState["Name"];
                return (s ?? String.Empty);
            }
            set
            {
                ViewState["Name"] = value;
            }

        }

        protected override void RenderContents(HtmlTextWriter output)
        {
            var sb = new StringBuilder();
            sb.AppendFormat(@"<input type=""hidden"" " + 
                            @"name=""{0}"" id=""{1}"" value=""{2}"" />", 
                            Name, ID, Value);

            output.Write(sb.ToString());
        }

    }
}

Since I am adding these tags dynamically via code, the HTML produced by ASP.NET will look something like below. ASP.NET added the span tags, but I can live with that.

<span id="ctl00_ctl07">
     <input type="hidden" name="CID" id="CID" value="123456" />
</span>
<span id="ctl00_ctl08">
      <input type="hidden" name="AMOUNT" id="AMOUNT" value="1" />
</span>

Here is some sample VB code to add an instance of the new control to your form:

Dim hidElem As New hiddenField()
hidElem.EnableViewState = False
hidElem.ID = id
hidElem.Name = id
hidElem.Value = val

Me.Form.Controls.Add(hidElem)

Solution 2

In the process of working through this, I found a better and much simpler solution. Apparently, Microsoft has already included the solution in the CLR.

Just use:

ClientScript.RegisterHiddenField("name","value")

One last thing

I also needed to post to a dynamic URL based off of a config file. I found I could set the form variables like this:

Me.Form.Method = "post"
Me.Form.Action = URL

Or even better, just include the URL in the PostBackUrl for the Button control.

buttonYes.PostBackUrl = URL