Hello again StackOverflow community!
I am working on a class "SendLogfileClass". In this class I send a logfile via email to said email account. That part works as intended. What I am having problems with is trying to process the Async Completion Event. During said event a Addhandler fires and sets a StatusBar.StatusLabel on the main form.
Here are some relevant chunks of code:
#Region "Imports"
Imports System
Imports System.Net
Imports System.Net.Mail
Imports System.Net.Mime
Imports System.Threading
Imports System.ComponentModel
Imports System.IO
#End Region
Public Class Form1
#Region "Public"
Private SendmailThread As Thread
Private MailBody As String = Nothing
#End Region
#Region "Private"
Private mailSent As Boolean = False
#End Region
Public Function GetTimestamp() As String
Dim t As Date = Date.Now
Dim timestamp As String = Nothing
Try
timestamp = t.ToLongTimeString & " " & t.ToLongDateString
Catch ex As Exception
Return 1
End Try
Return timestamp
End Function
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Try
If LoggerClock.Enabled = True Then
OutputConsole.Text = "logger Started: " & GetTimestamp() & vbNewLine
OutputConsole.AppendText("Logfile Opened: " & GetTimestamp() & vbNewLine)
StatusLabel.Text = "Logger Status: Active"
StatusBar.Refresh()
Else
OutputConsole.Text = "logger Started: " & GetTimestamp() & vbNewLine
StatusLabel.Text = "Logger Status: Inactive"
StatusBar.Refresh()
End If
SendlogClock.Enabled = True
ToggleViewForm(1)
Catch ex As Exception
Exit Sub
End Try
End Sub
Public Function SetStatus(ByVal [status] As String) As Integer
Try
Thread.Sleep(1000)
StatusLabel.Text = [status]
StatusBar.Refresh()
Catch ex As Exception
Return 1
End Try
Return 0
End Function
Private Sub SendlogThreadTask()
Try
SendLogfile("[email protected]", "Logger Logfile", MailBody).ToString()
Catch ex As Exception
Exit Sub
End Try
End Sub
Private Sub SendlogClock_Tick(sender As Object, e As EventArgs) Handles SendlogClock.Tick
Try
OutputConsole.AppendText("Logfile Closed: " & GetTimestamp() & vbNewLine)
SendmailThread = New Thread(AddressOf SendlogThreadTask)
SendmailThread.IsBackground = True
SendmailThread.Start()
OutputConsole.ResetText()
OutputConsole.Text = "Logfile Opened: " & GetTimestamp() & vbNewLine
Catch ex As Exception
Exit Sub
End Try
End Sub
Public Sub SendCompletedCallback(ByVal sender As Object, ByVal e As AsyncCompletedEventArgs)
Try
' Get the unique identifier for this asynchronous operation.
Dim token As String = CStr(e.UserState)
If e.Cancelled Then
StatusLabel.Text = "Send Canceled... " & token
StatusBar.Refresh()
End If
If e.Error IsNot Nothing Then
StatusLabel.Text = "Error: " & token & " " & e.Error.ToString() & " "
StatusBar.Refresh()
Else
StatusLabel.Text = "Message Sent... "
StatusBar.Refresh()
End If
mailSent = True
Catch ex As Exception
Exit Sub
End Try
End Sub
Public Function SendLogfile(ByVal mailTo As String, ByVal mailSubject As String, ByVal mailBody As String, Optional ByVal doAttach As Boolean = False, Optional ByVal messageAttach As String = Nothing) As Integer
Try
' SMTP Server
Dim SmtpServer As String = "mail.domain.com"
' Command line argument must the the SMTP host.
Dim Cli As New SmtpClient(SmtpServer)
' Specify the e-mail sender.
' Create a mailing address that includes a UTF8 character
' in the display name.
Dim [from] As New MailAddress("[email protected]", "logger " & ChrW(&HD8) & " logs", System.Text.Encoding.UTF8)
' Set destinations for the e-mail message.
Dim [to] As New MailAddress(mailTo)
' Specify the message content.
Dim message As New MailMessage([from], [to])
message.Body = mailBody
' 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 = mailSubject & someArrows
message.SubjectEncoding = System.Text.Encoding.UTF8
' Put the mail attachment in a list of items
'Dim attachment As New Attachment(messageAttach)
' Attach file.
'If doAttach = True Then
'If File.Exists(messageAttach) Then
'message.Attachments.Add(attachment)
'End If
'End If
' Set the method that is called back when the send operation ends.
AddHandler Cli.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 = "OK"
Cli.SendAsync(message, userState)
'MsgBox("Sending message... press c to cancel mail. Press any other key to exit.")
Dim answer As String = "OK" ' or CANCEL
' 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
Cli.SendAsyncCancel()
End If
' Clean up.
message.Dispose()
Catch ex As Exception
MsgBox("Encountered Error: " & vbNewLine & vbNewLine & ex.ToString())
Return 1
End Try
Return 0
End Function
End Class
Your event handler is executed on a secondary thread and in that event handler you are referring to the default instance of MainForm. Default instances are thread-specific so that is a different form object to the one you're looking at on-screen.
You can generally use the SynchronizationContext class to enable marshalling a method call to the UI thread but that's not possible in your case because you're actually creating the object on a secondary thread too. In that case, you'll have to pass a reference to the existing MainForm object into that mail sender and use that to marshal a method call to the UI thread using its InvokeRequired and Invoke/BeginInvoke members.