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Hi,
i have long running process in my BackgroundWorker_DoWork..
here:
the problem is i dont have a loop inside my DoWork.i cannot cancelled the worker thread immediately. any idea on this..Code:Private Sub BackgroundWorker1_DoWork(ByVal sender As Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
'Uploading XML File in remote server here
End Sub
thank you..
Here is an example off something I found on the web and tested a while ago:
Code:'From http://vbnotebookfor.net/2007/09/24/how-to-update-controls-using-backgroundworker-in-vbnet/
Public Class Form1
Private WithEvents BackGroundWorker As System.ComponentModel.BackgroundWorker
Private Sub btnStart_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnStart.Click
btnStart.Enabled = False
btnCancel.Enabled = True
lstValues.Items.Clear()
prgThread.Value = 0
BackGroundWorker = New System.ComponentModel.BackgroundWorker
BackGroundWorker.WorkerReportsProgress = True
BackGroundWorker.WorkerSupportsCancellation = True
BackGroundWorker.RunWorkerAsync()
End Sub
Private Sub BackGroundWorker_DoWork(ByVal sender As Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackGroundWorker.DoWork
Dim ListText As String
For Value As Integer = 0 To 100
If BackGroundWorker.CancellationPending Then
Exit For
End If
ListText = String.Concat("Item #", Value)
BackGroundWorker.ReportProgress(Value, ListText)
Threading.Thread.Sleep(100)
Next
End Sub
Private Sub BackGroundWorker_ProgressChanged(ByVal sender As Object, ByVal e As System.ComponentModel.ProgressChangedEventArgs) Handles BackGroundWorker.ProgressChanged
prgThread.Value = e.ProgressPercentage
lstValues.Items.Add(e.UserState)
End Sub
Private Sub btnCancel_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCancel.Click
BackGroundWorker.CancelAsync()
End Sub
Private Sub BackGroundWorker_RunWorkerCompleted(ByVal sender As Object, ByVal e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles BackGroundWorker.RunWorkerCompleted
btnStart.Enabled = True
btnCancel.Enabled = False
End Sub
End Class
jmcilhinney submited a nice example regarding background workers in the vb.net code bank.
Have a look here for more info it might help you out.
Hello, i already tested the examples posted by jmcilhinney..but i my case..i dont have a loop inside the DoWork...if i also place a loop inside it..i do not know what maximum number in for loop..like 100 as jm example..Quote:
Originally Posted by stavris
is it necessary to put a loop inside a DoWork...?Code:Private Sub BackGroundWorker_DoWork(ByVal sender As Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackGroundWorker.DoWork
Dim ListText As String
For Value As Integer = 0 To 100'is this number fix?
If BackGroundWorker.CancellationPending Then
Exit For
End If
ListText = String.Concat("Item #", Value)
BackGroundWorker.ReportProgress(Value, ListText)
Threading.Thread.Sleep(100)
Next
In the examples provided a repetitive task takes place hence the loops.
In your case you said
'Uploading XML File in remote server here
So I don't think that you need a loop no (I might however missunderstood what you are trying to achieve)
Essentially the do work part of your background worker will go ahead and do the task in hand on a separate thread...
You don't need to know in advance how many iterations of the loop are required: -Quote:
Originally Posted by [gja]
just becomes: -Code:
For i As Integer = 1 To 100
'Raise the ProgressChanged event in the UI thread.
worker.ReportProgress(i, i & " iterations complete")
'Perform some time-consuming operation here.
Threading.Thread.Sleep(250)
Next i
Code:
For i As Integer = 1 To X
' where X is the number you require (held in a global variable maybe).
'Raise the ProgressChanged event in the UI thread.
worker.ReportProgress(i, i & " iterations complete")
'Perform some time-consuming operation here.
Threading.Thread.Sleep(250)
Next i
If you're not performing a repetitive task then you don't need a loop. You aren't so you don't.
You don't need a loop to be able to cancel a background operation. What you do need is to be calling multiple methods in between which you can cancel the operation. If you can't test CancellationPending and set e.Cancel then you can't cancel the operation, plain and simple. If you can then you can.
this is what i have inside the DoWork...
is there any other way to forcely terminate the operation?(e.g large xml file upload)and a user decided to terminate it by clicking cancel button..if the system don't react to it..they might think that the cancel button was not working..Code:'Export XML
Dim objCookie As New CookieContainer
'Dim ls_headerData As String
Dim objUri As Uri
Dim objWebRequest As HttpWebRequest
Dim objWebResponse As HttpWebResponse = Nothing
Dim ls_boundary As String
Dim sb_builder As StringBuilder
Dim lbyte_postData() As Byte
Dim lbyte_boundary() As Byte
'Streams
Dim objFileStream As FileStream = Nothing
Dim objRequestStream As Stream = Nothing
Dim objStreamReader As StreamReader = Nothing
Dim li_length As Long
Dim li_bytesRead As Integer
Dim enc As ASCIIEncoding
Dim ls_readData As String
Dim ls_url As String
Try
'WriteToEventLog("Uploading Started" & ps_filename & ".")
ls_url = ps_url & "/test/exportxml.asp?Src=f0rm&devision=" & ps_dbname
objUri = New Uri(ls_url)
objWebRequest = CType(WebRequest.Create(objUri), HttpWebRequest)
ls_boundary = "--" & Now.ToString
'Initialize request object
objWebRequest.Credentials = New System.Net.NetworkCredential(ps_lnkUsername, ps_lnkPassword)
objWebRequest.UserAgent = "ASI"
objWebRequest.ContentType = "multipart/form-data; boundary=" & ls_boundary
objWebRequest.Method = "POST"
objWebRequest.KeepAlive = True
objWebRequest.CookieContainer = objCookie
objWebRequest.Timeout = 3600000 'added last 8/17/2010 by ryan
'Build the post header data
sb_builder = New StringBuilder
sb_builder.Append("--")
sb_builder.Append(ls_boundary)
sb_builder.Append(vbCrLf)
sb_builder.Append("Content-Disposition: form-data; name=""")
sb_builder.Append("XMLFile")
sb_builder.Append("""; filename=""")
sb_builder.Append(Path.GetFileName(ps_filename))
sb_builder.Append("""")
sb_builder.Append(vbCrLf)
sb_builder.Append("Content-Type: ")
sb_builder.Append("text/xml")
sb_builder.Append(vbCrLf)
sb_builder.Append(vbCrLf)
lbyte_postData = System.Text.Encoding.UTF8.GetBytes(sb_builder.ToString())
lbyte_boundary = Encoding.ASCII.GetBytes(vbCrLf & "--" + ls_boundary + vbCrLf)
objFileStream = New FileStream(ps_filename, FileMode.Open, FileAccess.Read)
li_length = lbyte_postData.Length + objFileStream.Length + lbyte_boundary.Length
objWebRequest.ContentLength = li_length
objRequestStream = objWebRequest.GetRequestStream()
' write the data to be posted to the Request Stream
objRequestStream.Write(lbyte_postData, 0, lbyte_postData.Length)
Dim lbyte_buffer(Math.Min(4096, CInt(objFileStream.Length))) As Byte
enc = New ASCIIEncoding
li_bytesRead = objFileStream.Read(lbyte_buffer, 0, lbyte_buffer.Length)
While li_bytesRead <> 0
objRequestStream.Write(lbyte_buffer, 0, li_bytesRead)
li_bytesRead = objFileStream.Read(lbyte_buffer, 0, lbyte_buffer.Length)
End While
objRequestStream.Write(lbyte_boundary, 0, lbyte_boundary.Length)
'Get the response
objWebResponse = CType(objWebRequest.GetResponse(), HttpWebResponse)
objStreamReader = New StreamReader(objWebResponse.GetResponseStream(), Encoding.Default)
ls_readData = objStreamReader.ReadToEnd()
'Transactions
If ParseHTMLResult(ls_readData) <> 0 Then
Throw New Exception("Some errors found while uploading XML document.")
End If
'XMLUpload = 1
'WriteToEventLog("Done Uploading " & ps_filename & "!")
Catch ex As WebException
'error was related to web connection
''WriteToEventLog("ERROR: " & ex.Message)
'XMLUpload = 2
Catch ex As Exception
'XMLUpload = 0
'WriteToEventLog("ERROR: " & ex.Message)
Finally
'Housekeeping
If Not objFileStream Is Nothing Then
objFileStream.Close()
End If
If Not objRequestStream Is Nothing Then
objRequestStream.Close()
End If
If Not objStreamReader Is Nothing Then
objStreamReader.Close()
End If
If Not objWebResponse Is Nothing Then
objWebResponse.Close()
End If
End Try
Like I said, the only way that you can cancel the operation is if you can test CancellationPending and set Cancel. You can do that in between any two lines of code insde the DoWork event handler. You can't do it "during" a line of code. If you call a method that runs for 10 minutes inside the DoWork event handler then you can terminate the operation before that method or after but not during. If you are providing the user a means to cancel and you have to wait for a while to actually cancel the operation in the DoWork event handler then it's up to you to design the app such that the IS aware that their cancellation has been registered but not implemented yet. You might do that by disabling the Cancel button and displaying a message somewhere (on the button, in a status bar, etc) to informs the user of exactly that. The user knows what you tell them.
pardon me,a little confused on this?Quote:
Originally Posted by jmcilhinney
as what u have all said..i convince that in my case im not gonna able to terminate the operation while it start uploading xml file.bcoz if it reach this code.this is the lines of code that takes time to process.bcoz it waiting for the response of a webservice..
if i still provide cancellation of operation it is still no use..bcoz if the upload method starts there is no way to terminate it.unless it reach to the end..Code:'Get the response
objWebResponse = CType(objWebRequest.GetResponse(), HttpWebResponse)
objStreamReader = New StreamReader(objWebResponse.GetResponseStream(), Encoding.Default)
You can provide the ability to cancel before calling GetResponse, after calling GetResponse and before calling GetResponseStream, and after calling GetResponseStream:I'm not 100% sure but I believe that the actual data doesn't get downloaded from the server until you read it from the stream. In that case you can cancel during the actual download if the download is broken up. Once you've got the StreamReader, you can also then read the data in chunks rather than in one block. That will allow you to cancel between chunks as well.Code:'You can cancel here
objWebResponse = CType(objWebRequest.GetResponse(), HttpWebResponse)
'You can cancel here
objStreamReader = New StreamReader(objWebResponse.GetResponseStream(), Encoding.Default)
'You can cancel here
You got it jm!...Thank you very much!...
Thank you also to people who reply my post...:-)