ASP .NET dropDownList problem

Diddy Kong

I have a drop down list which pulls data form a database, one value is selected and you click a button and it then displays (should) other details...i get "System.NullReferenceException: Object reference not set to an instance of an object." error when i click on the button to view the other details

any help much appreciated

The wonky bit of code:
strState=ddl1.SelectedItem.Text

Thats where it says the error is

thanks

Evil Phil

Can you post the code used to bind the control? My intial guess is you should be using

strState = ddl1.SelectedItem.Value

Diddy Kong

tried the value but the same problem code

<script language="VB" runat="server">
Dim MyArrayList as ArrayList
Dim sItem as String
Sub Page_Load(Source as Object, E as EventArgs)
MyArrayList=New Arraylist
if not Page.IsPostBack then
Dim strConn as string = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" & _
server.mappath("db1.mdb") & ";"
Dim MySQL as string = "Select PT_ID from TempDb"
Dim MyConn as New OleDbConnection(strConn)
Dim objDR as OleDbDataReader
Dim Cmd as New OleDbCommand(MySQL, MyConn)
MyConn.Open()
objDR=Cmd.ExecuteReader(system.data.CommandBehavior.CloseConnection)
While objDR.Read()
MyArrayList.add(objDR("PT_ID"))
End While
end if
ddl1.datasource=MyArrayList
ddl1.databind
End Sub

Sub doQuery(Source as Object, E as EventArgs)
Dim DS As DataSet
Dim MyConnection As OleDbConnection
Dim MyCommand As OleDbDataAdapter
Dim strState as string
strState=ddl1.SelectedItem.Text
Label1.Text="You chose: " + strState

Dim MySQL as string
MySQL="select DESC from TempDb where PT_ID='" & strState & "'"
panel1.visible="true"
label2.text=MySQL
MyConnection = New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" & _
server.mappath("db1.mdb") & ";")
MyCommand = New OleDbDataAdapter(MySQL, MyConnection)
DS = new DataSet()
MyCommand.Fill(ds, "TempDb")

MyDataGrid.DataSource=ds.Tables("TempDb").DefaultView
MyDataGrid.DataBind()
End Sub

</script>

Evil Phil

Okay try this:

Dim MyArrayList as ArrayList 
Dim sItem as String
Sub Page_Load(Source as Object, E as EventArgs)
   MyArrayList=New Arraylist 
   if not Page.IsPostBack then
      Dim strConn as string = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" & _
      server.mappath("db1.mdb") & ";"
      Dim MySQL as string = "Select PT_ID from TempDb"
      Dim MyConn as New OleDbConnection(strConn)
      Dim objDR as OleDbDataReader
      Dim Cmd as New OleDbCommand(MySQL, MyConn)
      MyConn.Open()
[color=green] 'Here's where I made my changes[/color]
      [color=red]ddl1.datasource=Cmd.ExecuteReader(system.data.CommandBehavior.CloseConnection)
      ddl1.DataValueField = "PT_ID"
      ddl1.databind[/color]
End Sub

This will bind the datareader PT_ID field directly to you dropdownlist and gets rid of the arraylists. You can then reference the value using the code I posted first, being:

strState = ddl1.SelectedItem.Value

Forgive my vb code, I'm a c# boy these days. Try it and let me know

Diddy Kong

its missing an end if.....where do you want me to stick that??

Diddy Kong

ok i took out the page.ispostback statement and it worked....

thanks for your help
very much appreciated

Diddy Kong

might have been a bit premature there....it isnt updating...take it thats what the page.isnotpostback was for......

Evil Phil

Dim MyArrayList as ArrayList 
Dim sItem as String
Sub Page_Load(Source as Object, E as EventArgs)
   MyArrayList=New Arraylist 
   if not Page.IsPostBack then
      Dim strConn as string = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" & _
      server.mappath("db1.mdb") & ";"
      Dim MySQL as string = "Select PT_ID from TempDb"
      Dim MyConn as New OleDbConnection(strConn)
      Dim objDR as OleDbDataReader
      Dim Cmd as New OleDbCommand(MySQL, MyConn)
      MyConn.Open()
[color=green] 'Here's where I made my changes[/color]
      [color=red]ddl1.datasource=Cmd.ExecuteReader(system.data.CommandBehavior.CloseConnection)
      ddl1.DataValueField = "PT_ID"
      ddl1.databind
   [b]end if[/b][/color]
End Sub

There you go, lazy bones

Diddy Kong

thank you very much.....