DropDowns and Post Back

Grodnik · February 19th, 2016, 07:42 PM

I have 2 dropdown lists. The second one is filled based on the selection in the first. I am using Autopostback = true and onselectedindexchanged in the first one to fill the second. It works fine except ... If I make a selection in the first dropdown so the second one is filled, and then go back and make a different selection in the first, the values from my original selection stay visible in the second. What do I need to do to refresh the data in the second dropdown?

Thank you.

Imar · February 21st, 2016, 08:33 AM

Hi there,

Is this related to a specific exercise in the book? If so, which chapter / page number does this refer to? And if not, you're better off posting this in the general ASP.NET category here: http://p2p.wrox.com/asp-net-4-5-709/

That said, depending on how you set up stuff you may need to call DropDown2.Items.Clear() or DropDown2.Bind() to get rid of the items.

Cheers,

Imar

karas75y · June 1st, 2016, 12:38 AM

I am having the same issue. This is Chapter 6 Page 239.

After following the instructions and even copy and paste the code from the source to the one I am creating still does not change the theme.

Any ideas or suggestions??

Code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class MasterPages_Frontend : System.Web.UI.MasterPage
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            string selectedTheme = Page.Theme;
            HttpCookie preferredTheme = Request.Cookies.Get("PreferredTheme");
            if (preferredTheme != null)
            {
                selectedTheme = preferredTheme.Value;
            }
            if (!string.IsNullOrEmpty(selectedTheme))
            {
                ListItem item = ThemeList.Items.FindByValue(selectedTheme);
                if (item != null)
                {
                    item.Selected = true;
                }
            }
        }
    }

    protected void ThemeList_SelectedIndexChanged(object sender, EventArgs e)
    {
        HttpCookie preferredTheme = new HttpCookie("PreferredTheme");
        preferredTheme.Expires = DateTime.Now.AddMonths(3);
        preferredTheme.Value = ThemeList.SelectedValue;
        Response.Cookies.Add(preferredTheme);
        Response.Redirect(Request.Url.ToString());
    }
}

karas75y · June 1st, 2016, 01:51 PM

Found the solution.

I think I was reading too fast and not paying attention to the details.

CH6 Page 242 step 6 it says on the botton "Notice that you keep seeing the same theme because you haven't written any code yet that applies the selected theme"

Page 243 shows how to do this code but step 4 (page 244) shows the reasons of why it might not work.
*Web.Config needs to be changed
*The most important Default page the Code behind needs to point to BasePage and not the default one.