un evento può restituire risposte al chiamante?

**pietro09** · 05-09-2006, 09:36

Originariamente inviato da djciko

non so aiutarti, ti seguo a fatica su quest'argomento...

mi segui a fatica forse... perchè ho un poco sbagliato il codice

comunque, se ti interessa ho una cosa un poco più interessante: se ti interessa mando il codice:

In una libreria ho una classe che ha il compito di intercettare l'html della pagina, permettere di cambiarlo, e rimandarlo al browser.
Una versione è realizzata con gli eventi, un'altra con i delegati.

**djciko** · 05-09-2006, 10:20

certo che interessa, posta posta

**pietro09** · 05-09-2006, 10:30

1° esempio con i delegati (è più semplice che con gli eventi)

file ResponseFilter.vb

codice:

Public Delegate Function DelegateSetHtml(ByVal html As String) As String
Public Class ResponseFilter
    Inherits Stream

    Private m_sink As Stream
    Private m_position As Long
    Private m_function As DelegateSetHtml


    Public Sub New(ByVal sink As Stream, ByVal functionHtml As DelegateSetHtml)
        Me.m_sink = sink
        Me.m_function = functionHtml
    End Sub

    Public Overrides ReadOnly Property CanRead() As Boolean
        Get
            Return True
        End Get
    End Property

    Public Overrides ReadOnly Property CanSeek() As Boolean
        Get
            Return False
        End Get
    End Property

    Public Overrides ReadOnly Property CanWrite() As Boolean
        Get
            Return False
        End Get
    End Property

    Public Overrides Sub Flush()
        Me.m_sink.Flush()
    End Sub

    Public Overrides ReadOnly Property Length() As Long
        Get
            Return 0
        End Get
    End Property

    Public Overrides Property Position() As Long
        Get
            Return Me.m_position
        End Get
        Set(ByVal Value As Long)
            Me.m_position = Value
        End Set
    End Property

    Public Overrides Function Read(ByVal buffer() As Byte, ByVal offset As Integer, ByVal count As Integer) As Integer
        Return Me.m_sink.Read(buffer, offset, count)
    End Function

    Public Overrides Function Seek(ByVal offset As Long, ByVal origin As System.IO.SeekOrigin) As Long
        Return 0
    End Function

    Public Overrides Sub SetLength(ByVal value As Long)
        Me.m_sink.SetLength(value)
    End Sub

    Public Overrides Sub Close()
        Me.m_sink.Close()

    End Sub

    Public Overrides Sub Write(ByVal buffer() As Byte, ByVal offset As Integer, ByVal count As Integer)
        Dim Html As String = System.Text.UTF8Encoding.UTF8.GetString(buffer, offset, count)
        Html = Me.m_function(Html)
        buffer = System.Text.UTF8Encoding.UTF8.GetBytes(Html)

        Me.m_sink.Write(buffer, 0, buffer.Length)


    End Sub

End Class

pagina di esempio intercettare html.aspx

codice:

<%@ Page Language="VB" AutoEventWireup="false" CodeFile="intercettare html.aspx.vb" Inherits="CorsoApogeo_leggere_il_contenuto_html_della_pagina_intercettare_html" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Pagina senza titolo</title>
    <link href="../../stili/Styles.css" rel="stylesheet" type="text/css" />
</head>
<body>
    <h1>Intercettare html con delegati</h1>
    <h3>PIETRO</h3>

    <form id="form1" runat="server">
        


            <asp:TextBox ID="TextBox1" runat="server">Nicola</asp:TextBox></p>
        


            <asp:TextBox ID="TextBox2" runat="server" Visible="false"></asp:TextBox></p>
        


            <asp:Button ID="Button1" runat="server" Text="Intercetta html"></asp:Button></p>
    </form>
</body>
</html>

codice sottostante

codice:

Option Strict On
Partial Class CorsoApogeo_leggere_il_contenuto_html_della_pagina_intercettare_html
    Inherits System.Web.UI.Page

    Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        'Inserire qui il codice utente necessario per inizializzare la pagina

    End Sub

    Private Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
        Me.Response.Filter = New ResponseFilter(Response.Filter, AddressOf modificaHtml)
    End Sub

    Public Function modificaHtml(ByVal html As String) As String
        Dim FileName As String = "c:\tmp\response.htm"

        Try
            html = html.Replace("PIETRO", "--- " & Me.TextBox1.Text & " ---")
            File.WriteAllText(FileName, html, Encoding.UTF8)

        Catch ex As Exception
            html &= "<script>alert('Errore nella scrittura del file');</script>"

        End Try

        Return html

    End Function

    Public Function modificaHtml_old(ByVal html As String) As String
        Dim fs As FileStream = Nothing
        Dim buffer As Byte()

        Try
            fs = New FileStream("c:\tmp\response.htm", FileMode.OpenOrCreate, FileAccess.Write)
            html = html.Replace("PIETRO", "----NICOLA---")
            buffer = System.Text.UTF8Encoding.UTF8.GetBytes(html)
            fs.Write(buffer, 0, buffer.Length)

        Catch ex As Exception
            html &= "<script>alert('Errore nella scrittura del file');</script>"

        Finally
            If Not (fs Is Nothing) Then fs.Close()
        End Try

        Return html

    End Function

End Class

2° esempio che fa uso degli eventi
file ResponseFilterWithEvent.vb

codice:

Public Class ResponseFilterWithEvent : Inherits Stream
    Public Event onHTML As onHTML

    Private m_sink As Stream
    Private m_position As Long


    Public Sub New(ByVal sink As Stream)
        Me.m_sink = sink
    End Sub

    Public Overrides ReadOnly Property CanRead() As Boolean
        Get
            Return True
        End Get
    End Property

    Public Overrides ReadOnly Property CanSeek() As Boolean
        Get
            Return False
        End Get
    End Property

    Public Overrides ReadOnly Property CanWrite() As Boolean
        Get
            Return False
        End Get
    End Property

    Public Overrides Sub Flush()
        Me.m_sink.Flush()
    End Sub

    Public Overrides ReadOnly Property Length() As Long
        Get
            Return 0
        End Get
    End Property

    Public Overrides Property Position() As Long
        Get
            Return Me.m_position
        End Get
        Set(ByVal Value As Long)
            Me.m_position = Value
        End Set
    End Property

    Public Overrides Function Read(ByVal buffer() As Byte, ByVal offset As Integer, ByVal count As Integer) As Integer
        Return Me.m_sink.Read(buffer, offset, count)
    End Function

    Public Overrides Function Seek(ByVal offset As Long, ByVal origin As System.IO.SeekOrigin) As Long
        Return 0
    End Function

    Public Overrides Sub SetLength(ByVal value As Long)
        Me.m_sink.SetLength(value)
    End Sub

    Public Overrides Sub Close()
        Me.m_sink.Close()

    End Sub

    Public Overrides Sub Write(ByVal buffer() As Byte, ByVal offset As Integer, ByVal count As Integer)
        Dim Html As String = System.Text.UTF8Encoding.UTF8.GetString(buffer, offset, count)
        Dim e As New ResponseFilterEventArgs()
        e.HTML = Html
        RaiseEvent onHTML(Me, e)
        Html = e.HTML
        buffer = System.Text.UTF8Encoding.UTF8.GetBytes(Html)

        Me.m_sink.Write(buffer, 0, buffer.Length)


    End Sub

End Class


'classe personale di evento
Public Class ResponseFilterEventArgs
    Private _HTML As String = ""
    Public Property HTML() As String
        Get
            Return Me._HTML
        End Get
        Set(ByVal value As String)
            Me._HTML = value
        End Set
    End Property
End Class

'delegate che definisce l'evento
Public Delegate Sub onHTML(ByVal sender As Object, ByVal e As ResponseFilterEventArgs)

la pagina di esempio è uguale alla prima, mentre il codice sottostante è:

codice:

Option Strict On

Partial Class CorsoApogeo_leggere_il_contenuto_html_della_pagina_intercettare_html_con_eventi
    Inherits System.Web.UI.Page

    Private Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
        'creo una istanza della classe ResponseFilterWithEvent
        Dim j As New ResponseFilterWithEvent(Me.Response.Filter)

        'aggancio l'evento onHTML
        AddHandler j.onHTML, AddressOf Me.modificaHtml

        'filtro l'html
        Me.Response.Filter = j

    End Sub


    'evento lanciato da ResponseFilterWithEvent
    Private Sub modificaHtml(ByVal Sender As Object, ByVal e As ResponseFilterEventArgs)
        'file su cui voglio salvare l'html
        Dim FileName As String = "c:\tmp\response.htm"

        'recupero l'html
        Dim html As String = e.HTML
        Try
            'modifico l'html
            html = html.Replace("PIETRO", "--- " & Me.TextBox1.Text & " ---")

            'scrivo la pagina html modificata
            File.WriteAllText(FileName, html, Encoding.UTF8)

        Catch ex As Exception
            'altrimenti messaggio di errore
            html &= "<script>alert('Errore nella scrittura del file');</script>"

        End Try
        'restituisco l'html modificato per essere mandato al browser
        e.HTML = html

    End Sub

End Class

ps. se trovi errori, io sono qui

**djciko** · 05-09-2006, 12:09

ok ma dopo mi ci vorra' un'altra settimana di ferie

perche' hai eliminato l'uso del buffer nel 1° esempio ? ricordo che anche in java con gli stream di bytes dava problemi, non puoi immaginare le nottate per mettere su un sistema di messaggistica

**pietro09** · 05-09-2006, 12:13

Originariamente inviato da djciko
ok ma dopo mi ci vorra' un'altra settimana di ferie

perche' hai eliminato l'uso del buffer nel 1° esempio ? ricordo che anche in java con gli stream di bytes dava problemi, non puoi immaginare le nottate per mettere su un sistema di messaggistica

è il primo esempio del tipo che faccio. Se lo migliori, ti sarei grato se lo comunicassi. ciao

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