[RESOLVED] Cancelling progress Background worker

[steve_rm]

Hello,

I am using the code below to login to a softphone. However, the login progess is a long process as there are many things that have to be initialized and checks to be made, I have only put a few on here, as it would make the code to long to post.

In the code below I am checking if the CancellationPending if the CancelAsync has been called in my cancel button click event, before doing each check. Is this correct? Also if the check fails I also call the CancelAsync and set the e.Cancel to true.

I would like to know if my method I have used here is the best method to use.

Many thanks for any advice,

Private Sub bgwProcessLogin_DoWork(ByVal sender As Object, ByVal e As DoWorkEventArgs)
'        
'         * Perform at test to see if the background worker has been
'         * cancelled by the user before attemping to continue to login.
'         * 
'         * Cancel background worker on any failed attemp to login
'         

		' Start with cancel being false as to reset this if cancel has been set to true
		' in the cancel button.
		e.Cancel = False

		Dim connection_test As New NetworkingTest()
		If (Not Me.bgwProcessLogin.CancellationPending) Then
			' Check local LAN or Wireless connection               
			If (Not connection_test.IsNetworkConnected()) Then
				' Update label
				If Me.lblRegistering.InvokeRequired Then
					Me.lblRegistering.Invoke(New UpdateRegisterLabelDelegate(UpdateRegisterLabel), "No network connection")
				Else
					Me.lblRegistering.Text = "No network connection"
				End If
				' Failed attemp
				Me.bgwProcessLogin.CancelAsync()
				e.Cancel = True
				Return
			End If
			' Report current progress
			Me.bgwProcessLogin.ReportProgress(0, "Network connected")
		Else
			' User cancelled 
			e.Cancel = True
			Return
		End If

		' Test if access to Server is available
		If (Not Me.bgwProcessLogin.CancellationPending) Then
			If (Not connection_test.IsSIPServerAvailable()) Then
				' Update label
				If Me.lblRegistering.InvokeRequired Then
					Me.lblRegistering.Invoke(New UpdateRegisterLabelDelegate(UpdateRegisterLabel), "Server unavailable")
				Else
					Me.lblRegistering.Text = "Server unavailable"
				End If
				' Failed attemp
				Me.bgwProcessLogin.CancelAsync()
				e.Cancel = True
				Return
			End If
			' Report current progress
			Me.bgwProcessLogin.ReportProgress(1, "Server available")
		Else
			' User cancelled 
			e.Cancel = True
			Return
		End If
	        .
                .
                .
End Sub

 Private Sub bgwProcessLogin_RunWorkerCompleted(ByVal sender As Object, ByVal e As RunWorkerCompletedEventArgs)
		' Check for any errors
		If e.Error Is Nothing Then
			If e.Cancelled Then
				' User cancelled login or login failed                
			Else
				' Login completed successfully                
			End If
		Else
			' Something failed display error
			Me.statusDisplay1.CallStatus = e.Error.Message
		End If
 End Sub

Private Sub bgwProcessLogin_ProgressChanged(ByVal sender As Object, ByVal e As ProgressChangedEventArgs)
		Me.lblRegistering.Text = e.UserState.ToString()
End Sub

Private Sub btnCancel_Click(ByVal sender As Object, ByVal e As EventArgs)
		' Cancel the logging in process
		Me.bgwProcessLogin.CancelAsync()
		Me.lblRegistering.Text = "Logged out"
End Sub

[jmcilhinney]

That's pretty much it except there's no point calling CancelAsync in the DoWork event handler. All calling CancelAsync does is set CancellationPending to True. CancelAsync is only useful when called from the UI thread in order to signal to the secondary thread that the operation should be cancelled, in which case e.Cancel is set to True and you return. If you're already in the secondary thread and you want to cancel then you would simply set e.Cancel to True and return, which you're already doing. Calling CancelAsync is redundant.