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SmtpClient.SendAsyncCancel Method

Cancels an asynchronous operation to send an e-mail message.

Namespace:  System.Net.Mail
Assembly:  System (in System.dll)

'Declaration
Public Sub SendAsyncCancel
'Usage
Dim instance As SmtpClient

instance.SendAsyncCancel()

ExceptionCondition
ObjectDisposedException

This object has been disposed.

Use the SendAsyncCancel method to cancel a pending SendAsync operation. If there is mail waiting to be sent, this method releases resources used to store the mail. If there is no mail waiting to be sent, this method does nothing.

The following code example demonstrates sending an e-mail message asynchronously. The user has the option to cancel the mail if it has not been sent.

Imports System
Imports System.Net
Imports System.Net.Mail
Imports System.Net.Mime
Imports System.Threading
Imports System.ComponentModel
Namespace Examples.SmptExamples.Async
    Public Class SimpleAsynchronousExample
        Private Shared mailSent As Boolean = False 
        Private Shared Sub SendCompletedCallback(ByVal sender As Object, ByVal e As AsyncCompletedEventArgs)
            ' Get the unique identifier for this asynchronous operation. 
            Dim token As String = CStr(e.UserState)

            If e.Cancelled Then
                Console.WriteLine("[{0}] Send canceled.", token)
            End If 
            If e.Error IsNot Nothing Then
                Console.WriteLine("[{0}] {1}", token, e.Error.ToString())
            Else
                Console.WriteLine("Message sent.")
            End If
            mailSent = True 
        End Sub 
        Public Shared Sub Main(ByVal args() As String)
            ' Command line argument must the the SMTP host. 
            Dim client As New SmtpClient(args(0))
            ' Specify the e-mail sender. 
            ' Create a mailing address that includes a UTF8 character 
            ' in the display name. 
            Dim [from] As New MailAddress("jane@contoso.com", "Jane " & ChrW(&HD8) & " Clayton", System.Text.Encoding.UTF8)
            ' Set destinations for the e-mail message. 
            Dim [to] As New MailAddress("ben@contoso.com")
            ' Specify the message content. 
            Dim message As New MailMessage([from], [to])
            message.Body = "This is a test e-mail message sent by an application. " 
            ' Include some non-ASCII characters in body and subject. 
            Dim someArrows As New String(New Char() {ChrW(&H2190), ChrW(&H2191), ChrW(&H2192), ChrW(&H2193)})
            message.Body += Environment.NewLine & someArrows
            message.BodyEncoding = System.Text.Encoding.UTF8
            message.Subject = "test message 1" & someArrows
            message.SubjectEncoding = System.Text.Encoding.UTF8
            ' Set the method that is called back when the send operation ends. 
            AddHandler client.SendCompleted, AddressOf SendCompletedCallback
            ' The userState can be any object that allows your callback  
            ' method to identify this send operation. 
            ' For this example, the userToken is a string constant. 
            Dim userState As String = "test message1"
            client.SendAsync(message, userState)
            Console.WriteLine("Sending message... press c to cancel mail. Press any other key to exit.")
            Dim answer As String = Console.ReadLine()
            ' If the user canceled the send, and mail hasn't been sent yet, 
            ' then cancel the pending operation. 
            If answer.StartsWith("c") AndAlso mailSent = False Then
                client.SendAsyncCancel()
            End If 
            ' Clean up.
            message.Dispose()
            Console.WriteLine("Goodbye.")
        End Sub 
    End Class 
End Namespace

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0
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