Question

I have a blank Repeater nested inside a column in a GridView and want to use a button in the GridView to populate the Repeater on demand via code behind. I am having difficulties referencing the repeater inside my button’s onCommand sub.

Here is the relevant markup:

<asp:GridView ID="Submission" runat="server" AllowPaging="true" AllowSorting="true" />
            <Columns>
                ..........
                <asp:TemplateField HeaderText="Action">
                    <ItemTemplate>
                        <asp:ImageButton ID="AdminEditSubmission" runat="server" ImageUrl="edit_15.png"
                            alt="" OnCommand="loadDetails" CommandArgument="X" />
                    </ItemTemplate>
                </asp:TemplateField>
                ..........
                <asp:TemplateField>
                    <ItemTemplate>
                                <asp:Repeater ID="RptSubmissionDetail" runat="server">
                                </asp:Repeater>
                    </ItemTemplate>
                </asp:TemplateField>
            </Columns>
        </asp:GridView>

For the sake of this small example, I will simply try to update the repeater’s header with “Hello world”. However, when it gets to the last line, I get the dreaded “Object reference not set to an instance of an object” error.

    Sub loadDetails(sender As Object, e As CommandEventArgs)
        Dim rpt As Repeater = CType(Page.FindControl("RptsSubmissionDetail"), Repeater)
        Dim tmpHdr As TemplateBuilder = New TemplateBuilder
        tmpHdr.AppendLiteralString("Hello World")
        rpt.HeaderTemplate = tmpHdr
    End Sub

Can anyone tell me how to reference this repeater from my ImageButton click sub? I have tried several, with Page.FindControl(“RptsSubmissionDetail”) only being my latest attempt.

Answer 1

In GridView’s RowCommand you need to use FindControl on the GridViewRow:

Sub Submission_RowCommand(ByVal sender As Object, ByVal e As GridViewCommandEventArgs)
    If e.CommandName = "loadDetails" Then
      ' Convert the row index stored in the CommandArgument
      ' property to an Integer.
      Dim index = Convert.ToInt32(e.CommandArgument)  
      ' Retrieve the row that contains the button clicked 
      ' by the user from the Rows collection.
      Dim row = Submission.Rows(index)  
      Dim repeater = DirectCast(row.FindControl("RptSubmissionDetail"), Repeater)
    End If
End Sub

From the ImageButton’s click event it’s nearly the same. Cast the sender argument to the ImageButton and it’s NamingContainer property to the GridViewRow. Then use FindControl as shown above:

Sub ImageButton_Click(ByVal sender As Object, ByVal e As EventArgs)
    Dim img = DirectCast(sender, ImageButton)
    Dim row = DirectCast(img.NamingContainer, GridViewRow)
    Dim repeater = DirectCast(row.FindControl("RptSubmissionDetail"), Repeater)
End Sub