SmtpClient.SendAsyncCancel Method ()
.NET Framework (current version)
Cancels an asynchronous operation to send an e-mail message.
Assembly: System (in System.dll)
| Exception | Condition |
|---|---|
| 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
.NET Framework
Available since 2.0
Available since 2.0
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