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Dynamically (programatically) adding check boxes and checkedchanged events

Answer 1

A:

If you have one Instructions textbox and one WorkPlaceHazards textbox per checkbox, then you have to have a way to associate the checkbox that was clicked with those other two controls.

If that's not the case, then what are they supposed to be doing?

casperOne 2009-03-09 16:08:25

Answer 2

A:

var box = new CheckBox();

Chris Holmes 2009-03-09 16:08:59

Answer 3

A:

When you say they "don't do anything" - are you getting the postback?

I wouldn't be surprised if you had to assign IDs to the checkboxes - bear in mind that on the postback, you'll get a new page, so it'll have to recreate all the checkboxes, then work out which one was checked etc. This is getting into what is (to me, anyway) somewhat black magic side of ASP.NET. I think you'll have to study the page life cycle and control identification side of things reasonably carefully.

Jon Skeet 2009-03-09 16:09:09

Answer 4

+1 A:

You should do the following:

Set the ID property for each instance of CheckBox you create in your foreach loop.
For PostBacks, ensure that your CheckBoxes are created and CheckedChanged event handler is attached at some point of the page life-cycle before control events are raised

Ken Browning 2009-03-09 16:10:53

Yup, my CheckBoxes were being eaten during postback

Comanighttrain 2009-03-10 15:39:06

Answer 5

A:

Make sure to verify you are doing the following:

The same list of checkbox is being added on both the initial load and further postbacks
You set a different ID to each checkbox
Verify you are getting a postback (set a break point in Page Load)
The controls are added to the page on Page Load, or even better on Page Init

If you are trying to do something different than that, update us with more info.

eglasius 2009-03-09 16:45:03

Answer 6

A:

You can get value by Request["controlname"] method when you inserted control in runtime.You must set Unique ID for each control.

However you can use CheckBoxList as an alternative instead of dynamically added checkboxes

2009-03-09 21:53:35

Answer 7

A:

I copied your code into a new VS2005 C# web project (see below). Your code works. There may be something else going on outside of this snippet. Or, is the StatementText property in all of your statements collection always empty?

Page...

<body>
    <form id="form1" runat="server">
    <div>
        <asp:PlaceHolder ID="PlaceHolder1" runat="server"></asp:PlaceHolder>
        Instructions: <asp:TextBox ID="Instructions" runat="server" />
        WorkPlaceHazardsBox: <asp:TextBox ID="WorkPlaceHazardsBox" runat="server" />
    </div>
    </form>

</body>

Code behind...

using System;
using System.Data;
using System.Configuration;
using System.Collections.Generic;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

namespace CheckboxMadness
{
    public partial class _Default : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            List<string> statements = new List<string>(new string[] { "foo", "bar" });

            foreach (string i in statements)
            {
                CheckBox box = new CheckBox();
                box.Text = i;
                box.AutoPostBack = true;
                box.CheckedChanged += new EventHandler(this.CheckedChange);
                PlaceHolder1.Controls.Add(box);
            }

        }
        protected void CheckedChange(object sender, EventArgs e)
        {
            CheckBox x = (CheckBox)sender;

            Instructions.Text = "change";

            WorkPlaceHazardsBox.Text += x.Text;
        }
    }
}

Aaron Daniels 2009-03-09 22:42:25

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Dynamically (programatically) adding check boxes and checkedchanged events

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