Notify user when thread has started and when it has finished?

[kutlesh]

Learning this VB.NET stuff and I am still not sure how to notify properly the user when exporting to excel has started and when it has finished.

I have this code:

Dim finished as Boolean = true

private sub exportToExcel()
 ' exporting code
end sub

Private Sub exportToExcelBtn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles exportToExcelBtn.Click
        finished = False
        statusBarTB.Text = "Exporting data to Excel file. "

        thread = New System.Threading.Thread(AddressOf exportToExcel)
        thread.Start()

        While Not thread.IsAlive
            statusBarTB.Text = "Finished recording data to Excel file! "
        End While
    End Sub

I tried with this "finished" boolean flag but the window gets stuck until the export has finished, which is not what I want. Why do i use thread in the first place if it freezes the window thread.

How can I properly notify user when thread has started and has finished?

Does VB.NET Threading API have stuff like addEventListener with which I can add functions and execute those on certain events?

[si_the_geek]

Your While loop is a busy-loop, which will keep the window too busy to do anything else.

One thing you could do is have add code at the end of the exportToExcel routine to set the value itself (by invoking), eg:

private sub exportToExcel()
 ' exporting code

  statusBarTB.Invoke(Sub() statusBarTB.Text = "Finished recording data to Excel file! ")
end sub

Note however that if this might also be run on the UI thread (rather than a new one), you should use InvokeRequired. There is more info about that here:
http://www.vbforums.com/showthread.p...he-UI-question


Alternatively you can add a BackgroundWorker to your form, which is a thread template that automatically has a Completed event that runs on the UI thread (no invoking required).

[Goggy]

You might want to look at the Backgroundworker class.
It has a "RunWorkerCompleted" event.

[TysonLPrice]

Here is a very nice example of a background worker with progress displayed.

'http://www.vbforums.com/showthread.php?680130-Correct-way-to-use-the-BackgroundWorker

[dbasnett]

Here is your code modified to use Task and Await. Note the UI will remain responsive while the task is running.

    Private Sub exportToExcel()
        ' exporting code
        Threading.Thread.Sleep(1000) 'simulate work
        'when complete
        finished.Set()
    End Sub

    Private finished As New Threading.ManualResetEvent(False)
    Private ThreadExp As Task
    Private Async Sub exportToExcelBtn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles exportToExcelBtn.Click
        finished.Reset()
        statusBarTB.Text = "Exporting data to Excel file. "

        ThreadExp = Task.Run(Sub() exportToExcel())
        Await ThreadExp
        statusBarTB.Text = "Finished recording data to Excel file! "
    End Sub