RE: Status Bar Updating and SQL Connections
From: Matt Garven (Matt_Garven_at_newsgroup.nospam)
Date: 02/10/05
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Date: Thu, 10 Feb 2005 15:01:12 -0800
Hi Max,
The problem is that you can't update the GUI from different threads. So it's
your main thread that needs to update the GUI and your new thread that needs
to do the work. Something like this...
Public Class IRISLogin
Private Sub cmdExport_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles cmdExport.Click
Dim sb_thread As New Thread(AddressOf DoWork)
sb_thread.Start()
While sb_thread.ThreadState = ThreadState.Running
UpdateStatusBar()
Thread.Sleep(1000)
End While
End While
End Sub
Private Sub DoWork()
' do work here
End Sub
"Max Turavani" wrote:
> Hi Matt,
>
> I have tried 3 different ways ( Timer Control, Timer CallBack ,
> System.Thread ). They all exhibit the same behaviour. I figured the
> System.Theading way would be the most reliable, here is some code:
>
> Public Class IRISLogin
>
> Dim waitText As String = "Please wait"
> Dim sb_thread As New Thread(AddressOf updateDisplay)
>
> 'status bar updating thread
> Private Sub updateDisplay()
> Dim c As Integer
> While Thread.CurrentThread.ThreadState = ThreadState.Running
> For c = 0 To 10
> waitText += "."
> sbStatus.Text = waitText
> Application.DoEvents()
> Application.DoEvents()
> Application.DoEvents()
> Application.DoEvents()
> Application.DoEvents()
> Thread.CurrentThread.Sleep(1000)
> Next
> waitText = "Please wait"
> End While
> End Sub
>
> Private Sub cmdExport_Click(ByVal sender As System.Object, ByVal e As
> System.EventArgs) Handles cmdExport.Click
>
> ' display a Save As dialog
> Dim sa_dlg As New SaveFileDialog
> sa_dlg.Filter = "txt files (*.txt)|*.txt|All files (*.*)|*.*"
> sa_dlg.Title = "Enter a file name for the IRIS Extract file"
>
> If sa_dlg.ShowDialog() = DialogResult.Cancel Then Exit Sub
> Dim saPath As String
> Dim recCount As Integer
>
> saPath = sa_dlg.FileName
> lSaveTo.Text = "Output file: " & saPath
> ' refresh screen before performing query to allow Windows to erase
> the Save As dialog box
> Application.DoEvents()
> ' THREAD IS SUPPOSED TO START HERE !!!!
> sb_thread.Start()
> Dim recAd As SqlDataAdapter
> Dim DBconn As New SqlConnection
> Dim DBcommand As New SqlCommand
>
> sbStatus.Text = "Getting records...please wait"
> Me.Cursor.Current = Cursors.WaitCursor
>
> DBconn.ConnectionString = SQL_CONN
> DBcommand.Connection = DBconn
> DBcommand.CommandType = CommandType.StoredProcedure
> DBcommand.CommandText = "dsbn_IRISExtract"
> 'set CommandTimeout to 0 for long queries !!!!
> DBcommand.CommandTimeout = 0
> DBcommand.Parameters.Add("@schoolYear", SqlDbType.VarChar).Value =
> cmdSchoolYear.SelectedItem
> Try
> recAd = New SqlDataAdapter(DBcommand)
> DBconn.Open()
> recAd.Fill(IRISRecs, "Recs")
> DBconn.Close()
> ' ONLY STARTS TO DISPLAY HERE !!!! '
> recCount = writeRecs(saPath)
> Me.Cursor.Current = Cursors.Default
> sbStatus.Text = "Done. " & recCount & " records processed"
> If MsgBox("Would you like to view the output file ?",
> MsgBoxStyle.Question & MsgBoxStyle.YesNo, "Trillium :: IRIS Data Extract
> Utility") = MsgBoxResult.Yes Then
> ' open Notepad to view the extract file
> Shell("notepad " & saPath, AppWinStyle.NormalFocus, False)
> End If
> Catch ex As SqlClient.SqlException
> Me.Cursor.Current = Cursors.Default
> MsgBox(ex.Message, MsgBoxStyle.Critical, "Critical Error")
> sbStatus.Text = String.Empty
> Exit Sub
> End Try
> End Sub
>
> Pretty standard stuff, but for some reason the thread does not work here. As
> a test, if I start the thread in the Load event it chugs along until the SQL
> query starts. Then it just stops. When the query is finished, it starts up
> again. Very frustrating.
> Thanks for your help !!!
> Max
>
>
>
> "Matt Garven" wrote:
>
> > Hi Max,
> >
> > Do you launch a worker thread and use a timer on the form to keep the dots
> > moving? You could try adding a call to Application.DoEvents() after you've
> > modified your dots, however it shouldn't be necessary.
> >
> > Can you provide a small sample of what you're doing?
> >
> > Regards,
> > Matt Garven
> >
> > "Max Turavani" wrote:
> >
> > > Hi,
> > >
> > > I have a simple Windows Forms app that connects to a SQL server, extracts
> > > about 50,000 records and saves them to a file. During the query, I have a
> > > small bit of text on a status bar that increments a period (.) every second
> > > to show the user that the app is still running and not hung. I have used
> > > timers, timer threading and system threading to increment the "dot" in a
> > > separate thread with no problem UNTIL I execute the query using
> > > SQLDataAdapter. While the query proc is being run the dots just stop
> > > incrementing..As soon as the query is done, the dataset is filled, the "dots"
> > > begin to increment again. Not what I intended. It seems that the UI thread is
> > > still running but never gets enough CPU time to update the status bar on the
> > > screen. Is there anyway to give that UI updating thread enough time to update
> > > the screen or do I have to run the SQL Query routine in it's own thread. Any
> > > help would be greatly appreciated ?
> > >
> > > Max
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