#眉標=.NET Namespace專欄
#副標= System.NET
#大標=要求─回應模式的通訊作業
#作者=文／彭靖灝
#引言=對於大多數的通訊作業而言，要求─回應的作業模式應該是很常見的應用。在System.Net命名空間中，微軟提供了一組處理這類作業模式的類別：WebResponse和WebRequest。
#內文=

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Dim request As WebRequest = 
WebRequest.Create("http://www.flag.com.tw")
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=========程式=========
程式1 透過WebRequest和WebResponse進行存取

Imports System.Net
Imports System.Text
Imports System.IO

…

Private Sub btnGO_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnGO.Click
StatusStrip1.Text = "Creating Request..."
Dim request As WebRequest = _
WebRequest.Create(txtURI.Text)

' 準備身份資訊.
StatusStrip1.Text = "Preparing Credential..."
request.Credentials = CredentialCache.DefaultCredentials

' 取得回應
StatusStrip1.Text = "Waiting for Response..."
Dim response As WebResponse = _
request.GetResponse()

' 顯示狀態
Dim strResult As New StringBuilder
StatusStrip1.Text = "Request Success! Preparing for content..."
strResult.Append _
("Status:" & response.StatusDescription & vbNewLine)

' 取得內容串流
Dim dataStream As Stream = response.GetResponseStream()

' 安排串流內容
Dim myEncoding As Encoding = Encoding.GetEncoding(950)
Dim reader As New StreamReader(dataStream, myEncoding)

' 讀取內容
Dim responseFromServer As String = reader.ReadToEnd()

' 顯示內容
strResult.Append(responseFromServer)
txtResponse.Text = strResult.ToString
 
' 清除串流及物件
reader.Close()
dataStream.Close()
response.Close()
End Sub
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程式2
 ' 取得回應
Dim response As HttpWebResponse = _
CType(request.GetResponse(), HttpWebResponse)

' 顯示狀態
Dim strResult As New StringBuilder
strResult.Append("Status:" & _
response.StatusDescription & vbNewLine)
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=========程式=========
程式3
Dim request As HttpWebRequest = _
WebRequest.Create(myUri)
request.Accept = "image/*"
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程式4
Public Class State
    Public Request As HttpWebRequest

    Public Sub New()
        Request = Nothing
    End Sub
End Class
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程式5
Private Sub btnGO_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnGO.Click
Dim request As HttpWebRequest = _
WebRequest.Create(txtURL.Text)
  Dim myState As New State

  myState.Request = request
  request.BeginGetResponse( New AsyncCallback _
(AddressOf ReceiveResponse), myState)
End Sub
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程式6
Private Sub ReceiveResponse(ByVal request As IAsyncResult)
Dim myState As State = CType(request.AsyncState, State)
Dim HttpRequest As HttpWebRequest = myState.Request
Dim response As HttpWebResponse = _
HttpRequest.EndGetResponse(request)

      …

Display(strResult.ToString)

End Sub
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程式7
Dim myCache As New CredentialCache()    

myCache.Add(New Uri("http://www.mysite.com/"), "Basic", _
New NetworkCredential(UserName, SecurelyStoredPassword))
myCache.Add(New Uri("http://www.mysite.com/"), "Digest", _
New NetworkCredential(UserName, _
SecurelyStoredPassword, Domain))
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程式8
Dim myCredential As NetworkCredential = _
myCache.GetCredential(New Uri(txtURI.Text), "Basic")
request.Credentials = myCredential
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程式9 處理WebException
Try
   …

Catch ex As WebException
Dim StatusDesc As String

If ex.Status = WebExceptionStatus.ProtocolError Then
txtResponse.Text = "Error:" & ex.Message & _
vbNewLine & "Status Code:" & _
CType(ex.Response, HttpWebResponse).StatusCode & _
vbNewLine & "Status Description:" & _
CType(ex.Response, HttpWebResponse).StatusDescription
Else
StatusDesc = _
WebExceptionStatus.GetName( _
GetType(WebExceptionStatus), ex.Status)
txtResponse.Text = "Error:" & ex.Message & _
vbNewLine & "Status Description:" & StatusDesc
End If
End Try

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=========程式=========
Dim client As New WebClient
Dim myCredential As New NetworkCredential("anonymous", "")
client.Credentials = myCredential
client.DownloadFile("ftp://localhost/myFile.txt", _
"C:\My Documents\myFile.txt") 
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=========程式=========
Dim uri As String = "ftp://localhost/myFile.txt"
Dim request As FtpWebRequest = _
CType(WebRequest.Create(uri), FtpWebRequest)
request.Method = WebRequestMethods.Ftp.DeleteFile
Dim response As FtpWebResponse = _
CType(request.GetResponse(), FtpWebResponse)
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=========程式=========
程式10

Private Sub btnSend_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnSend.Click
    Dim Msg As New MailMessage

    With Msg
        .To = txtTo.Text
        .Subject = txtSubject.Text
        .Body = txtSubject.Text
    End With

    Try
        SmtpMail.SmtpServer = "localhost"
        SmtpMail.Send(Msg)
        MessageBox.Show("Mail sent.")
    Catch ex As Exception
        MessageBox.Show(ex.Message)

    End Try

End Sub
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程式11
Dim Msg As System.Net.Mail.MailMessage
Dim SendFrom, SendTo As MailAddress
Dim Client As New SmtpClient

SendFrom = New MailAddress("administrator@mysite.com")
SendTo = New MailAddress(txtTo.Text)
Msg = New System.Net.Mail.MailMessage(SendFrom, SendTo)
With Msg
    .Subject = txtSubject.Text
    .Body = txtBody.Text
End With
Client.Host = "localhost"
Try
    Client.Send(Msg)
    MessageBox.Show("Mail sent!")
Catch ex As SmtpException
    MessageBox.Show(ex.Message)
End Try
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