how do i get a handle on a listbox in page_load

lcsgeek · June 13th, 2006, 02:25 PM

I have a nested DropDownListBox inside of a DataList - see below.Ã Ã I have autopostback enabled on the ddlb and on PageLoad I want to Response.Redirect("someOtherPage.aspx?cid=" & lbClasses.SelectedValue().ToString()).Ã Ã Ever ything is working except the PageLoad keeps erring with "Object reference not set to an instance of an object" on the Response.Redirect line.Ã Ã I assume its because I'm not getting a handle on the listbox in order to harvest the selectedValue.Ã Ã Can anyone muddle through this message and code and advise, Please.

Code:

<asp:DataList ID="dlListName" runat="server" DataSourceID="sdsCategories" RepeatColumns="2" RepeatDirection="Horizontal">
    <ItemTemplate>
        <div class="categoryName"><asp:Label ID="itemDescriptionLabel" runat="server" Text='<%# Bind("classCategory") %>'></asp:Label><br />
            <asp:ListBox ID="lbClasses" runat="server" Rows="6" Width="228px" AutoPostBack="true"></asp:ListBox>Ã </div>
    </ItemTemplate>
    <ItemStyle CssClass="itemStyle" />
    <AlternatingItemStyle CssClass="alternatingItemStyle" /></asp:DataList>
<asp:SqlDataSource ID="sdsCategories" runat="server" ConnectionString="<%$ ConnectionStrings:LcsWebData %>"
    SelectCommand="SELECT DISTINCT classCategory FROM usrtbl_Classes WHERE (classCategory <> N'NA') ORDER BY classCategory">
</asp:SqlDataSource>

Code:

    Protected Sub dlListName_ItemDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.DataListItemEventArgs) Handles dlListName.ItemDataBound

        Dim row As DataRowView

        If e.Item.ItemType = ListItemType.Item Or e.Item.ItemType = ListItemType.AlternatingItem Then
            row = DirectCast(e.Item.DataItem, DataRowView)
            Dim conn As SqlConnection = Nothing
            Dim cmd As SqlCommand
            Dim ds As New DataSet()
            Dim parmCategoryName As New SqlParameter("@CategoryName", SqlDbType.NVarChar)

            conn = New SqlConnection(ConfigurationManager.ConnectionStrings("LcsWebData").ConnectionString)
            conn.Open()
            cmd = New SqlCommand()
            cmd.Connection = conn
            cmd.CommandText = "dbo.usp_getClassNamesPerClassCategory"
            cmd.CommandType = CommandType.StoredProcedure
            parmCategoryName.Direction = ParameterDirection.Input
            parmCategoryName.Value = row("classCategory").Trim()
            cmd.Parameters.Add(parmCategoryName)

            Dim ad As New SqlDataAdapter(cmd)

            ad.Fill(ds)

            lbClasses = DirectCast(e.Item.FindControl("lbClasses"), ListBox)
            lbClasses.DataSource = ds
            lbClasses.DataTextField = "className"
            lbClasses.DataValueField = "classId"
            lbClasses.DataBind()
            conn.Close()
        End If
    End Sub

Code:

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        If IsPostBack() Then
            Response.Redirect("class.aspx?cid=" & lbClasses.SelectedValue().ToString())
        End If
    End Sub

Code:

Public lbClasses As ListBox

jbenson001 · June 14th, 2006, 01:12 PM

You can't refence it that way since it is in a template column. You need to get a refernce to the object in the ItemDatabound event of the datalist

lcsgeek · June 19th, 2006, 08:13 AM

I appreciate your response, however I can't find anything practical in it's content.

Quote:

quote:You need to get a refernce to the object in the ItemDatabound event of the datalist

I haven't a clue as to what you mean by this statement, can you be more specific?

jbenson001 · June 19th, 2006, 09:20 AM

Datalist ItemDataBoundEvent:
        If e.Item.ItemType = ListItemType.Item Or e.Item.ItemType = ListItemType.AlternatingItem Then
           Dim lb as New ListBox
           lb = e.Item.FindControl("lbClasses")
           ''Do what you need to do here with the listbox.
        End If