Qualcuno mi sa dire perchè il seguente codice per effettuare un edit in un datalist popolato da un database:
<%@ Page Language="VB" Debug="true" %>
<%@ Import Namespace="System.Data" %>
<%@ Import Namespace="System.Data.Oledb" %>
<%@ Import Namespace="System.Data.SqlClient" %>
<%@ Import Namespace="System.Object" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<script runat="server">
' The Cart and CartView objects temporarily store the data source
' for the DataGrid control while the page is being processed.
Dim Conta As Integer
Dim Cart As DataTable = New DataTable()
Dim CartView As DataView
Dim Cart1 As DataSet
Dim Partenza As Integer
Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
' With a database, use an select query to retrieve the data. Because
' the data source in this example is an in-memory DataTable, retrieve
' the data from session state if it exists; otherwise create the data
' source.
GetSource()
' The DataGrid control maintains state between posts to the server;
' it only needs to be bound to a data source the first time the page
' is loaded or when the data source is updated.
End Sub
Sub DataList1_EditCommand(ByVal sender As Object, ByVal e As DataListCommandEventArgs)
' Set the EditItemIndex property to the index of the item clicked
' in the DataGrid control to enable editing for that item. Be sure
' to rebind the DateGrid to the data source to refresh the control.
DataList1.EditItemIndex = e.Item.ItemIndex
BindGrid()
End Sub
Sub DataList1_CancelCommand(ByVal sender As Object, ByVal e As DataListCommandEventArgs)
' Set the EditItemIndex property to -1 to exit editing mode.
' Be sure to rebind the DateGrid to the data source to refresh
' the control.
DataList1.EditItemIndex = -1
BindGrid()
End Sub
Sub DataList1_UpdateCommand(ByVal sender As Object, ByVal e As DataListCommandEventArgs)
' Retrieve the text boxes that contain the values to update.
' For bound columns, the edited value is stored in a TextBox.
' The TextBox is the 0th control in a cell's Controls collection.
' Each cell in the Cells collection of a DataGrid item represents
' a column in the DataGrid control.
Dim IdCatText As System.Web.UI.WebControls.TextBox = CType(e.Item.FindControl("IdCategoria"), TextBox)
Dim CatText As System.Web.UI.WebControls.TextBox = CType(e.Item.FindControl("Categoria"), TextBox)
Dim DesCatText As System.Web.UI.WebControls.TextBox = CType(e.Item.FindControl("Descrizione"), TextBox)
Dim IdCat As String = IdCatText.Text
Dim Cat As String = CatText.Text
Dim DesCat As String = DesCatText.Text
Dim MyConnection As OleDbConnection
Dim StringSelect As String
Dim UpDateCmd As String
Dim OleDbUpDateCmd As OleDbCommand
MyConnection = New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0; " & _
"Data Source=" + Server.MapPath("db\NWIND.mdb"))
MyConnection.Open()
StringSelect = "select * from Categorie"
UpDateCmd = "UPDATE Categorie SET NomeCategoria='" & Cat & "',Descrizione='" & DesCat & "' WHERE IdCategoria=" & IdCat
OleDbUpDateCmd = New OleDbCommand(UpDateCmd, MyConnection)
OleDbUpDateCmd.ExecuteNonQuery()
OleDbUpDateCmd.Connection.Close()
DataList1.EditItemIndex = -1
Session("ShoppingCart") = Nothing
GetSource()
' Retrieve the updated values.
End Sub
Sub BindGrid()
' Set the data source and bind to the Data Grid control.
DataList1.DataSource = CartView
DataList1.DataBind()
End Sub
Sub GetSource()
' For this example, the data source is a DataTable that is stored
' in session state. If the data source does not exist, create it;
' otherwise, load the data.
Dim DS As DataSet
Dim MyConnection As OleDbConnection
Dim MyCommand As OleDbDataAdapter
Dim quanti As Integer
Dim StringSelect As String
If Session("ShoppingCart") Is Nothing Then
MyConnection = New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0; " & _
"Data Source=" + Server.MapPath("db\NWIND.mdb"))
MyConnection.Open()
StringSelect = "select * from Categorie"
MyCommand = New OleDbDataAdapter(StringSelect, MyConnection)
DS = New DataSet()
MyCommand.Fill(DS, "tabella1")
' in quanti viene inserito il numero di record della tabella
quanti = DS.Tables("tabella1").Rows.Count.ToString()
Dim source As DataView = DS.Tables("tabella1").DefaultView
DataList1.DataSource = DS
DataList1.DataBind()
MyConnection.Close()
' Store the table in session state to persist its values
' between posts to the server.
Session("ShoppingCart") = DS.Tables("tabella1")
' Populate the DataTable with sample data.
End If
Cart = CType(Session("ShoppingCart"), DataTable)
' Create a DataView and specify the field to sort by.
CartView = New DataView(Cart)
End Sub
</script>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title>Untitled Page</title>
</head>
<body>
<form id="Form2" runat="server">
<font face="Verdana" size="-1">
<aspataList id="DataList1" runat="server"
BorderColor="black"
BorderWidth="1"
GridLines="Both"
CellPadding="3"
CellSpacing="0"
Font-Names="Verdana"
Font-Size="8pt"
Width="150px"
HeaderStyle-BackColor="#aaaadd"
AlternatingItemStyle-BackColor="Gainsboro"
EditItemStyle-BackColor="lightgreen"
OnEditCommand="DataList1_EditCommand"
OnUpdateCommand="DataList1_UpdateCommand"
OnCancelCommand="DataList1_CancelCommand"
>
<HeaderTemplate>
Items
</HeaderTemplate>
<ItemTemplate>
<asp:LinkButton id="button1" runat="server" Text="Edit" CommandName="edit" />
<%#DataBinder.Eval(Container.DataItem, "IdCategoria")%>
</ItemTemplate>
<EditItemTemplate>
Identificativo:
<asp:Label id="Label1" runat="server"
Text='<%# DataBinder.Eval(Container.DataItem, "IdCategoria") %>' />
Categoria:
<asp:TextBox id="Text1" runat="server"
Text='<%# DataBinder.Eval(Container.DataItem, "NomeCategoria") %>' />
Descrizione:
<asp:TextBox id="Text2" runat="server"
Text='<%# DataBinder.Eval(Container.DataItem, "Descrizione") %>' />
<asp:LinkButton id="button2" runat="server" Text="Update"
CommandName="update" />
<asp:LinkButton id="button3" runat="server" Text="Cancel"
CommandName="cancel" />
</EditItemTemplate>
</asp
</font>
</form>
</form>
</body>
Mi restituisce il seguente errore:
Riferimento a un oggetto non impostato su un'istanza di oggetto.
Descrizione: Eccezione non gestita durante l'esecuzione della richiesta Web corrente. Per ulteriori informazioni sull'errore e sul suo punto di origine nel codice, vedere l'analisi dello stack.
Dettagli eccezione: System.NullReferenceException: Riferimento a un oggetto non impostato su un'istanza di oggetto.
Errore nel codice sorgente:
Riga 68: Dim CatText As System.Web.UI.WebControls.TextBox = CType(e.Item.FindControl("Categoria"), TextBox)
Riga 69: Dim DesCatText As System.Web.UI.WebControls.TextBox = CType(e.Item.FindControl("Descrizione"), TextBox)
Riga 70: Dim IdCat As String = IdCatText.Text
Riga 71: Dim Cat As String = CatText.Text
Riga 72: Dim DesCat As String = DesCatText.Text
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