CODEWITHSUNDEEP
c#asp.netsqllistbox
Nico
Nico

Reputation: 237

C# SelectedValue in a Listbox

I'm adding data to my listbox using this code : 

    SqlCommand cmd1 = new SqlCommand("SELECT U_Naam, U_Voornaam, User_ID FROM Login ORDER BY U_Naam ASC", con);
    dr = cmd1.ExecuteReader();

    int teller = 0;

    while (dr.Read())
    {
        hulp = dr["U_Naam"].ToString() + " " + dr["U_Voornaam"].ToString();
        lbNiet.Items.Add(hulp);
        lbNiet.Items[teller].Value = dr["User_ID"].ToString();
        teller++;
    }

When I run the program and select an item in the list I want to get it's value (Using selectedvalue). When I do this it allways gives a nullref (no value). I've read somewhere the selected item is lost after a postback ? How can I solve this ?

thanks !

Upvotes: 0

Views: 1250

Answers (6)

gen
gen

Reputation: 405

you can use Request.Form to find the posted value
or I think if you use a scriptmanager and an updatepanel it refills the box after a postback

Upvotes: 0

Muhammad Akhtar
Muhammad Akhtar

Reputation: 52241

replace these lines

lbNiet.Items.Add(hulp);
lbNiet.Items[teller].Value = dr["User_ID"].ToString();

with

lbNiet.Items.Add(new ListItem(hulp,dr["User_ID"].ToString();));

Upvotes: 3

VMAtm
VMAtm

Reputation: 28355

Are you using the ViewState for your page?

If yes, check the IsPostBack property of the page, and don't populate your list after postback.

Upvotes: 0

Streklin
Streklin

Reputation: 849

I don't think the selected item is lost after PostBack under normal circumstances - my guess is that you are accidently populating the ListBox again after PostBack so that when you make a selection, the system hits the Page_Init / Page_Load (or whatever event you choose to populate the ListBox in) and recreates all the options. Doing this would overwrite the currently selected option.

If that's the case it's easily avoided by check for PostBack first before repopulating the list.

Upvotes: 2

Mr47
Mr47

Reputation: 2655

Databinding your data instead of adding in a loop will help.

Upvotes: 0

Tim
Tim

Reputation: 15227

Are you running that code in the Load of your ASP.NET page without checking to see if it is a Postback? You should make sure to wrap your loading code in a if (!IsPostback) {} block if you're doing it in the load of the page.

Upvotes: 1

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