Populate A Dropdown From Another Dropdown

I have a page that has two dropdowns on it. When the page loads, the first box is populated from an Access table. Here's the tricky part for me...

(Just when I think I understand how "postback" works, I find I'm wrong again!)

I have the dropdown set to autopostback=true. When the user selects a choice in this dropdown, the page postsback (I think) and I want it to then query another table in the same database to fill the second dropdown list AND keep the original dropdown list's selection.

For some reason, I can get it to fill the original dropdown, but then when it postsback, I get an error because my SQL statement to load the second dropdown looks like this:

Dim objSeriesDA As New OleDb.OleDbDataAdapter("SELECT * FROM Series WHERE fldProviderID=" & lstProvider.SelectedItem.Value & " ORDER BY fldSeriesNumber DESC", objSeriesCN)

Apparently, when the page postsback, the original dropdown list loses its selection, causing the SQL statement above to error out on a null reference.

Any ideas?

If need be, I can throw this up on a server so you all can see what I'm talking about... I can post the full source as well.

Thanks!

HWKY
:)wrap the code that is filling your first drop down list with this:

If Not Page.IsPostBack Then
'...your code here.
End If
Does anyone have a link to some information that explains PostBack in depth?
well, this link (http://www.15seconds.com/Issue/020102.htm) helped me with some basics on the page lifecycle when i was having user control postback problems. Really, there's not much more to the kind of postback stuff in your first post. If you know how the page loads and when control events are evaluated, that's pretty much it. Were you looking for information on how to roll your own PostBack handler or something else?

populate my datagrid RESOLVED

im trying to fill my datagrid but when the page loads in the browser you cant even see it.
wots going on there then here is the code,

Imports System
Imports System.data
Imports System.Data.SqlClient

Public Class WebForm1
Inherits System.Web.UI.Page

#Region " Web Form Designer Generated Code "

'This call is required by the Web Form Designer.
<System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()

End Sub
Protected WithEvents txt_mobile_number As System.Web.UI.WebControls.TextBox
Protected WithEvents txt_name As System.Web.UI.WebControls.TextBox
Protected WithEvents btn_submit As System.Web.UI.WebControls.Button
Protected WithEvents DataGrid1 As System.Web.UI.WebControls.DataGrid

'NOTE: The following placeholder declaration is required by the Web Form Designer.
'Do not delete or move it.
Private designerPlaceholderDeclaration As System.Object

Private Sub Page_Init(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Init
'CODEGEN: This method call is required by the Web Form Designer
'Do not modify it using the code editor.
InitializeComponent()
End Sub

#End Region

' declare the data set and data adapters
Private dsUsers As New DataSet
Private daUsers As New SqlDataAdapter



Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load



End Sub

Private Sub loadusers()
'connect to database

Dim oSQLConn As SqlConnection = New SqlConnection
oSQLConn.ConnectionString = "Data Source=(local);" & _
"Initial Catalog=Con_Test;" & _
"Integrated Security=SSPI"
oSQLConn.Open()

'databind the infromation

'If SqlConnection1.State = ConnectionState.Closed Then SqlConnection1.Open()
daUsers.SelectCommand = New SqlCommand("SELECT * from table_user", oSQLConn)
daUsers.Fill(dsUsers, "Mobile")
DataGrid1.DataSource = dsUsers.Tables(0)
DataGrid1.DataBind()
oSQLConn.Close()
'daUsers.Fill(dsUsers)
'DataGrid1.DataSource = dsUsers.Tables(0)

End Sub


End ClassDoes your dataset contain any data ?
If there is no row in the DataTable, you will not see the Datagrid on the page.
im trying to fill my datagrid but when the page loads in the browser you cant even see it.

Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load



End Sub

What else do you expect with an empty Page_Load event :p
ii called loadusers now in the page load an now i am gettin an error that
'invalid object name table_user', thats the table name within Con_test.
:eek2:
Has it been spelt right in the database?
top man mendhank, i know it seemed obvious with the error message but i never would have checked it,
u da man
Not a problem, we all learn... :)

Populating a listbox from DB w/o postback

Hi,

I have 2 listboxes. The first gets populated from the db as soon as the page loads. The second listbox get populated based on the user's selection from the first listbox. However, currently the code is such that with each selection there is a postback. We want to avoid it using filter and javascript. I am not using ADO.NET but adodbc and no datagrids or datasets (please don't tell me that i should as my boss clearly doesn't want to get into it at this stage).

How can i do it?

Thanks

Currently the code with the postback is as follows:
page_load

if not page.ispostback then
Do While Not rs.EOF
li = New ListItem(rs("cat_name").Value, rs("cat_id").Value)
List1.Items.Add(li)
rs.MoveNext()
Loop

End If

'List1.SelectedIndex = 0
rs.Close()
rs = Nothing

List1.SelectedValue = cat_id

'here there is some other code not relevant to the listboxes

'select items for second listbox
Dim rsSub As New ADODB.Recordset
rsSub.Open("SELECT sub_name, sub_id FROM subs WHERE cat_id=" & cat_id.ToString & " ORDER BY sub_name ASC", cn)
Dim l_item As ListItem
Do While Not rsSub.EOF
l_item = New ListItem(rsSub("sub_name").Value, rsSub("sub_id").Value)
List2.Items.Add(l_item)
rsSub.MoveNext()
Loop

List2.SelectedValue = sub_id

rsSub.Close()
rsSub = Nothing

cn.Close()
End If
' End If

End If

End Sub

Protected Sub Select1Change(ByVal sender As System.Object, ByVal e As System.EventArgs)

Dim cn As New ADODB.Connection
cn.Open(YBayTools.Constants.ConnectionString)

Dim rs As New ADODB.Recordset
Dim li As ListItem

rs.Open("Select * from subs where cat_ID =" & List1.SelectedItem.Value.ToString, cn)
'rs.Open("Select * from subs where cat_ID ='" & List1.SelectedItem.Text.ToString & "' & List1.SelectedItem.value.ToString", cn)

Dim strCat As String

If List2.Items.Count > 0 Then
List2.Items.Clear()
End If

If rs.BOF And rs.EOF Then
Response.Write("no records found")
Else

Do While Not rs.EOF
li = New ListItem(rs("sub_name").Value, rs("sub_id").Value)
List2.Items.Add(li)
rs.MoveNext()

Loop

End If

rs.Close()
rs = Nothing
cn.Close()You code is done to work with postback. So write client-site code with javascript on the first listBox and in this code, read the DB and populate you other listBox.
That's the thing I am not sure how to write it in jscript.
I need to get the data for both listboxes from a db.
You can use an XmlHttp object from client-side script, but this will probably only work on IE and Mozilla. Other solutions could use a lot of script and hidden frames (beuark!)