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microsoft.public.dotnet.framework.aspnet.webcontrols

Pre-Populate Dropdownlist?

heestand

2/22/2004 3:51:00 PM

I have a simple web app I am building: a user fills out a simple form
(regform.aspx) and clicks "OK" and they get a confirmation page
(confirmation.aspx) that repeats back what they entered before they
move on. I want the user to be able to go back to the first page from
the confirmation page and change values if they want. Seems simple,
no? I was going to use session state to pre-fill in the values on the
simple form on page_load if they are returning to it from the
confirmation page. I can do this for textboxes but when I try it for
a dropdown list I get ""Object reference not set to an instance of an
object." Here is a simplified version of my code. Thanks for any
help in advance:

RegForm.aspx
-------------
<%@ Page Language="VB" Inherits="RegFormCodeBehind"
Src="RegForm.aspx.vb" %>
<form name="RegForm" method="post" action="RegForm.aspx"
runat="server">
<asp:textbox ID="txtName" runat="server" /><br>
<asp:dropdownlist ID="ddlAge" runat="server">
<asp:listitem>Choose one...</asp:listitem>
<asp:listitem Value="25">25</asp:listitem>
<asp:listitem Value="26">27</asp:listitem>
</asp:dropdownlist>
....

RegForm.aspx
-------------
Public Class RegFormCodeBehind
Inherits System.Web.UI.Page

Public txtName as Textbox
Public ddlYear as Dropdownlist

Public Sub Page_Load(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles MyBase.Load
txtName.Text = "test value"
ddlAge.SelectedIndex = 1
End Sub
End Class

How do you set dropdownlists from code?

Thanks in advance!
-----------------
2 Answers

Alvin Bruney

2/22/2004 4:48:00 PM

0

Your dropdownlist has no items in it so it will blow up if you try to set
the index to 1 since the items are probably zero. The common approach is to
save the items in an array and cache the array. Then cache the selected
index that the user chose
Consider:

ArrayList arr = new ArrayList();
arr.Add(new listitem("item1","val1"));
arr.Add(new listitem("item2","val2"));
arr.Add(new listitem("item3","val3"));
Session["Items"] = arr;

[snip]
dropdownlist1.DataSource = arr;
dropdownlist1.DataBind();

//user selects item 1
Session["Selection"] = dropdownlist1.SelectedIndex.ToString();

[snip]
//coming back to the page
ArrayList arr = Session["Items"] as ArrayList;
if(arr!= null)
{
dropdownlist1.DataSource = arr;
dropdownlist1.DataBind();
if(Session["Selection"] != null)
{
int i = Int32.Parse(Session["Selection"].ToString());
if (i > Dropdownlist1.items.count)
Dropdownlist1.selectedindex = i;
}
}

roughly
--
Regards,
Alvin Bruney [ASP.NET MVP]
Got tidbits? Get it here...
http://tinyurl...
"DOUGLAS HEESTAND" <heestand@alumni.duke.edu> wrote in message
news:8e66a971.0402220751.428a2329@posting.google.com...
> I have a simple web app I am building: a user fills out a simple form
> (regform.aspx) and clicks "OK" and they get a confirmation page
> (confirmation.aspx) that repeats back what they entered before they
> move on. I want the user to be able to go back to the first page from
> the confirmation page and change values if they want. Seems simple,
> no? I was going to use session state to pre-fill in the values on the
> simple form on page_load if they are returning to it from the
> confirmation page. I can do this for textboxes but when I try it for
> a dropdown list I get ""Object reference not set to an instance of an
> object." Here is a simplified version of my code. Thanks for any
> help in advance:
>
> RegForm.aspx
> -------------
> <%@ Page Language="VB" Inherits="RegFormCodeBehind"
> Src="RegForm.aspx.vb" %>
> <form name="RegForm" method="post" action="RegForm.aspx"
> runat="server">
> <asp:textbox ID="txtName" runat="server" /><br>
> <asp:dropdownlist ID="ddlAge" runat="server">
> <asp:listitem>Choose one...</asp:listitem>
> <asp:listitem Value="25">25</asp:listitem>
> <asp:listitem Value="26">27</asp:listitem>
> </asp:dropdownlist>
> ...
>
> RegForm.aspx
> -------------
> Public Class RegFormCodeBehind
> Inherits System.Web.UI.Page
>
> Public txtName as Textbox
> Public ddlYear as Dropdownlist
>
> Public Sub Page_Load(ByVal sender As System.Object, ByVal e As
> System.EventArgs) Handles MyBase.Load
> txtName.Text = "test value"
> ddlAge.SelectedIndex = 1
> End Sub
> End Class
>
> How do you set dropdownlists from code?
>
> Thanks in advance!
> -----------------

heestand

2/24/2004 8:36:00 PM

0

That fixed it. Thanks so much!