Tipp 0019 HTML-Seite auslesen
Autor/Einsender:
Datum:
  Alex Wenig
15.09.2003
Entwicklungsumgebung:   VB.Net 2002
Framework:   1.0
Die Klasse HttpWebRequest, Namespace System.Net, stellt eine HTTP-spezifische Implementierung der WebRequest-Klasse bereit. WebRequest und WebResponse sind abstrakte Basisklassee (MustInherit in Visual Basic) für den Zugriff auf Daten im Internet. Mit Hilfe bestimmter Methoden beider Klassen kann ein Stream ausgelesen (System.IO.StreamReader) und wie in diesem Beispiel, in einer Multiline-Textbox angezeigt werden.
 
Imports System.Net
Imports System.IO

Public Class Form1
  Inherits System.Windows.Forms.Form
Vom Windows Form Designer generierter Code
  Private Sub Button1_Click(ByVal sender As System.Object, _
          ByVal e As System.EventArgs) Handles Button1.Click
    pbrPercent.Value = (0)
    txtHtml.Text = ""
    If txtAddress.Text <> "" Then
      If Not txtAddress.Text.TrimStart.Substring(0, 7) = _
              "http://" Then
        txtAddress.Text = "http://" & txtAddress.Text
      End If

      txtHtml.Text = GetHTMLPage(txtAddress.Text)
    Else
      MsgBox("Geben Sie eine Internetadresse ein.", _
            MsgBoxStyle.Exclamation)
    End If
  End Sub

  Public Function GetHTMLPage(ByVal URL As String) As String
    Dim sResult As String
    Dim oHttp As HttpWebRequest
    Dim objResponse As WebResponse
    Dim objRequest As WebRequest

    Try
      objRequest = System.Net.HttpWebRequest.Create(URL)

      objRequest.Method = "GET"
      objRequest.Timeout = 120000
      objResponse = objRequest.GetResponse

      ProgressBarinPercent(URL, pbrPercent)

      Dim sr As System.IO.StreamReader = _
            New System.IO.StreamReader( _
            objResponse.GetResponseStream(), _
            System.Text.Encoding.UTF7)

      sResult = sr.ReadToEnd()

      sr.Close()
      objResponse.Close()

      Return sResult

    Catch ex As System.Exception
      MsgBox(ex.Message)

      pbrPercent.Value = (0)
      txtHtml.Text = ""

      oHttp = Nothing
      objResponse = Nothing
      objRequest = Nothing
    End Try
  End Function

  Function ProgressBarinPercent(ByVal sURL As String, _
        ByVal pProgress As ProgressBar)

    Const APPROXFILESIZE As Integer = 80000

    Dim wRemote As System.Net.WebRequest
    Dim bBuffer(999) As Byte
    Dim sResponseData As String
    Dim iBytesRead As Integer

    wRemote = WebRequest.Create(sURL)
    pProgress.Maximum = APPROXFILESIZE

    Dim sChunks As Stream = wRemote.GetResponse.GetResponseStream

    Do
      iBytesRead = sChunks.Read(bBuffer, 0, 1000)
      If pProgress.Value + iBytesRead <= pProgress.Maximum Then
        pProgress.Value += iBytesRead
      Else
        pProgress.Value = pProgress.Maximum
      End If
    Loop Until iBytesRead = 0

    pProgress.Value = pProgress.Maximum
    sChunks.Close()

  End Function

  Private Sub Button2_Click(ByVal sender As System.Object, _
          ByVal e As System.EventArgs) Handles Button2.Click
    Me.Close()
  End Sub
End Class
 
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Letzte Aktualisierung: Samstag, 21. Januar 2012