Question

This is my datalist:

    <asp:DataList ID="DataList1" runat="server" DataSourceID="SqlDataSource1" 
               RepeatLayout="Flow">
            <ItemTemplate>

                <asp:Label ID="IdLabel" runat="server" Text='<%# Eval("ID") %>'  Visible="False" />
                Titre:
                <asp:Label ID="TitreLabel" runat="server" Text='<%# Eval("Titre") %>' />
                <br />
                Description:
                <asp:Label ID="DescriptionLabel" runat="server" 
                    Text='<%# Eval("Description") %>' />
                <br />

                <asp:Image ID="Image1" runat="server" 
                 ImageUrl='<%# Eval("ID", "Handler.ashx?ID={0}") %>' Width="200" Height="200"/>

                <br />
                comments:
                <asp:Label ID="commentsLabel" runat="server" Text='<%# Eval("comments") %>' />
                <br />

                Ajouter commentaire 
                <asp:button ID="btnAjouter"  runat="server" OnCommand="Button_Command"
                 CommandName="add" Text="Ajouter" />
                <asp:TextBox ID="TextBoxComments" runat="server"></asp:TextBox>
                <br/>
                <br/>
            </ItemTemplate>
        </asp:DataList>

This my aspx.vb button event:

Sub Button_Command(ByVal sender As Object, ByVal e As CommandEventArgs)
    Dim connectionString As String = WebConfigurationManager.ConnectionStrings("BecsEtMuseauxSQL").ConnectionString
    Dim con As SqlConnection = New SqlConnection(connectionString)

    con.Open()

    Dim cmd As New SqlCommand("updateComments", con)
    cmd.CommandType = CommandType.StoredProcedure
    //I try this ....
    cmd.Parameters.Add("@id", SqlDbType.Int).Value = DataList1.FindControl("IdLabel").ToString()
    cmd.Parameters.Add("@Comments", SqlDbType.NVarChar).Value = DataList1.FindControl("TextBoxComments").ToString()

    cmd.ExecuteNonQuery()
End Sub

I get an error like this: “The object reference is not definied to an object instance”

How can I catch the value from the label IdLabel and TextBoxComments in this situation?

Answer 1

You should handle the DataList’s ItemCommand instead of the Button’s Command.

Then you can find your controls with e.Item.FindControl:

Private Sub DataList1_ItemCommand(source As Object, e As System.Web.UI.WebControls.DataListCommandEventArgs) _
    Handles DataList1.ItemCommand
    If e.CommandName = "add" Then
        Dim IdLabel = DirectCast(e.Item.FindControl("IdLabel"), Label)
        Dim TextBoxComments = DirectCast(e.Item.FindControl("TextBoxComments"), TextBox)
        ' ... '
    End If
End Sub

on aspx, remove your redundant Command-handler:

<asp:button ID="btnAjouter" CommandName="add"  Text="Ajouter" runat="server" />

If you want to use the Button’s Click-Event instead, that’s possible also.

Protected Sub btnAjouter_Click(sender As Object, e As EventArgs)
    Dim container = DirectCast(DirectCast(sender, Control).NamingContainer, DataListItem)
    Dim IdLabel = DirectCast(container.FindControl("IdLabel"), Label)
    Dim TextBoxComments = DirectCast(container.FindControl("TextBoxComments"), TextBox)
    ' ... '
End Sub

on aspx, add the click-event handler to the button:

<asp:button ID="btnAjouter" OnClick="btnAjouter_Click" Text="Ajouter" runat="server" />