Question

這是我的數據列表：

<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> 

這是我aspx.vb按鈕事件：

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 

我得到這樣一個錯誤：「對象引用不definied對象實例」

我怎樣才能趕上從標籤IdLabel和TextBoxComments在這種情況下的價值？

Answer 1

您應該處理DataList's ItemCommand，而不是按鈕的命令。

然後你就可以用e.Item.FindControl找到您的控件：

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 

上ASPX，免除您的冗餘Command -handler：如果你想使用按鈕的點擊事件，而不是

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

，這是也可能。

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 

上ASPX，點擊事件處理程序添加到按鈕：

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