Using FindControl to locate controls in an ASP.Net DetailsView from a VB.Net code-behind file not working

Question

I'm looking to get FindControl to "see" controls in an ASP.Net DetailsView from a VB.Net code-behind file. It doesn't find any of them.

The markup for the page is using a MasterPage.

<%@ Page 
    Title="Attendance" 
    Language="vb" 
    AutoEventWireup="false" 
    MasterPageFile="~/Knowledge Academy.Master" 
    CodeBehind="Attendance.aspx.vb" 
    Inherits="Knowledge_Academy.Attendance" %>

<asp:Content 
    ID="ContentBody" 
    ContentPlaceHolderID="BodyPlaceholder" 
    runat="server">

Currently the attributes of a our DetailsView looks like this:

<asp:DetailsView 
            ID="DetailsView" 
            runat="server" 
            AutoGenerateRows="False" 
            Height="50px" 
            Width="207px" 
            DataSourceID="SqlDataSourceDetails"
            DataKeyNames="ID"
            OnItemCommand="DetailsViewDetails_ItemCommand">

            <Fields>

Can you tell me what additional attributes to include so coding like this can "see" the fields in the DetailsView?

Protected Sub DetailsViewDetails_ItemCommand(sender As Object, e As System.Web.UI.WebControls.DetailsViewCommandEventArgs)

    Select Case e.CommandName

        Case "Add"

        Case "Edit"
            ButtonAddNewAttendance.Enabled = False

        Case "Delete"

        Case "Update"
            ButtonAddNewAttendance.Enabled = True

        Case "Insert"

        Case "New"

            Dim txtBox As TextBox
            txtBox = DetailsView.FindControl("TextBoxDateAttendanceTakenInsert")
            txtBox.Text = DateTime.Now

            Dim drpValue As DropDownList
            drpValue = DetailsView.FindControl("DropDownListClassInsert")
            drpValue.SelectedValue = 1
    End Select
End Sub

Currently FindControl can't find any of the fields in the DetailsView and gives a Null reference error.

UPDATE *

ItemCommand is not the correct place to put the coding.

I found out that to get this to work, OnDataBinding needs to be added as shown here plus making sure there is a handler in the code-behind file as shown below.

InsertItemTemplate markup:

<InsertItemTemplate>
    <asp:DropDownList 
        ID="DropDownListClassInsert" 
        Runat="server"
        DataSourceID="SqlDataSourceClasses"
        DataTextField = "ClassName"
        DataValueField="ID"
        SelectedValue='<%# Bind("ClassID") %>'
        AppendDataBoundItems="True"
        ForeColor="Blue"
        OnDataBinding="DropDownListClassInsert_DataBinding">
    </asp:DropDownList>

    <asp:RequiredFieldValidator ID="RequiredFieldValidatorInsertClass" runat="server" ControlToValidate="DropDownListClassInsert" 
        ErrorMessage="Please select a Class here." Font-Bold="True" Font-Italic="True" ForeColor="Red" 
        SetFocusOnError="True" Display="Dynamic">
    </asp:RequiredFieldValidator>
</InsertItemTemplate>

Handler in the code-behind file:

Protected Sub DropDownListClassInsert_DataBinding(sender As Object, e As EventArgs)

    Dim drpValue As DropDownList
    drpValue = DetailsView.FindControl("DropDownListClassInsert")
    drpValue.SelectedValue = intCurrentClassID
End Sub

Note: intCurrentClassID is declared as:

Public Shared intCurrentClassID As Integer = Nothing

after:

Public Class

I hope this helps others who had the same issues.

score 0 · Answer 1 · answered Jan 07 '13 at 19:25

0

I believe that you want to use the Fields property instead of FindControl. Once you have the DataControlField, you can cast it to the appropriate control type (i.e. CheckBoxField).

answered Jan 07 '13 at 19:25

competent_tech

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Thanks for the reply. Can you show sample coding based on our existing code? Thanks. – Emad-ud-deen Jan 07 '13 at 19:32
@Emad-ud-deen: Sure, but I would need to see a little bit more code in order to supply this (which is why I didn't attempt to do this in the answer). Can you show the code in the context of where you are trying to use it? – competent_tech Jan 07 '13 at 19:34
Ok. I will edit the posting to show the complete sub routine. – Emad-ud-deen Jan 08 '13 at 13:51

Using FindControl to locate controls in an ASP.Net DetailsView from a VB.Net code-behind file not working

1 Answers1