Listbox dropdown SelectedIndex resets after postback

  • Thread starter Thread starter devNorway
  • Start date Start date
D

devNorway

I have been struggling with a problem for days now, and searched for
related problems and solutions but had no luck.

I have two dropdown listboxes where the first is populated in page load
and the second is populated based on the input in the first. The first
dropdown is inside a "If Not Page.IsPostBackThey" if loop. Both have
autopostback set to true.

The problem is that when the user makes a choice in the first dropdown
an event is triggered that will populate the second dropdown. This
works okay, I can acess the selectedindex inside the code behind so
that the second dropdown gets populated.

The problem is to retrieve the choice that is made in the second
dropdown. I try to save the selctedItem.text or the selectedIndex but
always this is set to 1.

I have seen that a lot of other programmers have had this problem where
the second dropdown gets binded a second time before the selected
values could get retrieved. This could normally get resolved by putting
the binding inside a if not page.ispostback loop, but not in this case
where i can not bind the second drop down after a choice is made in the
first dropdown.

Im wondering if I have a bug somewhere. Have tried Enabling Viewstate
to no luck.

Im adding some code here, any help would be appreciated.


-----

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

If Not Page.IsPostBack Then
GetMainResearchData()
GetSubResearchData(0)
lstMainCategory.Items.Insert(0, New ListItem("Please Select
Main Category", "None"))
lstMainCategory.SelectedIndex = 0
End If
End Sub

Private Sub lstMainCategory_SelectedIndexChanged(ByVal sender As
System.Object, ByVal e As System.EventArgs) Handles
lstMainCategory.SelectedIndexChanged
mainKey = lstMainCategory.SelectedIndex()
GetSubResearchData(mainKey)
End Sub

Private Sub lstSubCategory_SelectedIndexChanged(ByVal sender As
System.Object, ByVal e As System.EventArgs) Handles
lstSubCategory.SelectedIndexChanged
subKey = lstSubCategory.SelectedIndex() ' HERE THE VALUE IS ALWAYS
1
Session("subid") = subKey
End Sub


Private Sub GetMainResearchData()
Dim sqlText As String = "SELECT main_category_key,
main_category_title FROM ntnu_main_category ORDER BY
main_category_title"
Dim myCommand As SqlCommand = New SqlCommand(sqlText,
myConnection)

Try
myConnection.Open()
myDataReader =
myCommand.ExecuteReader(CommandBehavior.CloseConnection)
lstMainCategory.DataSource = myDataReader
lstMainCategory.DataBind()

Catch myException As Exception
Response.Write("Feilmelding " & myException.ToString())
Finally
If Not myDataReader Is Nothing Then
myDataReader.Close()
myConnection.Close()
End If
End Try
End Sub

Private Sub GetSubResearchData(ByVal mainCategory As Integer)

Dim sqlText As String = "SELECT sub_category_key,
sub_category_title FROM ntnu_sub_category WHERE
ntnu_sub_category.sub_category_key = " & mainCategory & ""
Dim myCommand As SqlCommand = New SqlCommand(sqlText,
myConnection)
Try
myConnection.Open()
myDataReader =
myCommand.ExecuteReader(CommandBehavior.CloseConnection)
lstSubCategory.DataSource = myDataReader
lstSubCategory.DataBind()
lstSubCategory.Items.Insert(0, New ListItem("Please Select
sub category", "None"))
lstSubCategory.SelectedIndex = 0

Catch myException As Exception
Response.Write("Feilmelding " & myException.ToString())
Finally
If Not myDataReader Is Nothing Then
myDataReader.Close()
myConnection.Close()
End If
End Try
End Sub
 
I looked at your SQL query and i'm wondering if sub_category_key is unique
for each of the items you are returning in the GetSubResearchData function,
if not (sa your query suggests) and you are binding the sub_category_key to
the value field of the second dropdown then you actually have just one item
from the dropdown's point of view .

look at the HTML source for the second dropdown and make sure that the
values differ for each of the items.

let me know if this helps
 
Thanks for your reply:)

I noticed this also but since im trying only to retrieve the
selectedIndex this shouldnt be a problem?

Im really not using the Values of the second dropdwon for anything..
 
Found the soution thanks to Onwuka Emeka here. I tried adding a primary
key for each sub category and used these for the listbox values. Then I
could easily retrieve the correct selectedIndex.
 
Back
Top