'Oftype' is not a member of 'controlcollection' in web forms

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VB

WebForms

Hello, i have a problem with my syntax in RowDataBound. I Want to create deleteing row in gridview without database and then i find a problem in RowDataBound. please help me (sry bad english)

What I have tried:

In .aspx

<pre><asp:GridView ID="gvPluPlano" runat="server" AutoGenerateColumns="False" AllowPaging="True" OnPageIndexChanging="gvPluPlano_PageIndexChanging" OnRowDeleting="gvPluPlano_RowDeleting" EmptyDataText="No records has been added." PageSize="500" ShowHeaderWhenEmpty="True" AllowSorting="True" headerstyle-cssclass="FixedHeader" Width="850px" style="margin-top: 0px" >
                        <HeaderStyle BackColor="Black" ForeColor="White" />
                        <RowStyle BackColor="White" ForeColor="Black" Wrap="false" />
                        <AlternatingRowStyle BackColor="#e5e5e5" ForeColor="Black" />
                        <SelectedRowStyle BackColor="#999999" ForeColor="#fff" />
                        <Columns>
                            <asp:TemplateField HeaderText="PLU" HeaderStyle-CssClass="header-center" ItemStyle-HorizontalAlign="Center" ItemStyle-Width="150">
                                <ItemTemplate>
                                    <asp:Label ID="lblPlu" runat="server" Text='<%# Eval("NAMAPLU") %>'></asp:Label>
                                </ItemTemplate>
                                <EditItemTemplate>
                                    <asp:TextBox ID="txtPlu" runat="server" MaxLength="8" Text='<%# Eval("NAMAPLU") %>'></asp:TextBox>
                                </EditItemTemplate>
                                <HeaderStyle CssClass="header-center"></HeaderStyle>
                                <ItemStyle HorizontalAlign="Center" Width="100px"></ItemStyle>
                            </asp:TemplateField>
                            <asp:TemplateField HeaderText="Description PLU" HeaderStyle-CssClass="header-center" ItemStyle-Width="150">
                                <ItemTemplate>
                                    <asp:Label ID="lblDescriptionPlu" runat="server" Text='<%# Eval("DESKRIPSIPLU") %>'></asp:Label>
                                </ItemTemplate>
                                <EditItemTemplate>
                                    <asp:TextBox ID="txtDescriptionPlu" runat="server" MaxLength="100" Text='<%# Eval("DESKRIPSIPLU") %>'></asp:TextBox>
                                </EditItemTemplate>
                                <HeaderStyle CssClass="header-center"></HeaderStyle>
                                <ItemStyle Width="200px"></ItemStyle>
                            </asp:TemplateField>
                            <asp:TemplateField ShowHeader="False">
                                <ItemTemplate>
                                    <asp:LinkButton ID="LinkButton1" runat="server" OnClientClick="return confirm('Are you sure you want to delete?'); " CausesValidation="False" CommandName="Delete" Text="Delete"></asp:LinkButton>
                                </ItemTemplate>
                                <ItemStyle Width="50px" HorizontalAlign="Center" />
                            </asp:TemplateField>
                        </Columns>
                    </asp:GridView>

in .Vb

Protected Sub gvPluPlano_RowDataBound(sender As Object, e As GridViewRowEventArgs)
        If e.Row.RowType = DataControlRowType.DataRow Then
            Dim item As String = e.Row.Cells(0).Text
            For Each button As Button In e.Row.Cells(2).Controls.OfType(Of Button)()
                If button.CommandName = "Delete" Then
                    button.Attributes("onclick") = "if(!confirm('Do you want to delete " + item + "?')){ return false; };"
                End If
            Next
        End If
    End Sub

    Protected Sub gvPluPlano_RowDeleting(sender As Object, e As GridViewDeleteEventArgs)
        Dim Index As String = txtPlu2.Text
        Dim dt As DataTable = TryCast(ViewState("dt"), DataTable)
        dt.Rows(Index).Delete()
        ViewState("dt") = dt
        LoadData()
    End Sub