Task function within form and error messages - vb.net

Question

I have a form whose role is to show the user a circular progress graphic while the user is waiting on particular stuff to be done. This is the simple code of it:
Public Class FrmCircularProgress
Sub New(progressType As DevComponents.DotNetBar.eCircularProgressType)
InitializeComponent()
CircularProgress1.ProgressBarType = progressType
StartCircular()
End Sub
Public Sub StartCircular()
Me.CircularProgress1.IsRunning = True
End Sub
Public Sub StopCircular()
Me.CircularProgress1.IsRunning = False
End Sub
End Class
Below is an example of how I use it (in this case two places)
Dim createArticle As New Artikel
'http://stackoverflow.com/questions/33030706/put-long-running-method-into-task-showing-new-form-meantime-and-closing-it-once
Dim pic As New FrmCircularProgress(eCircularProgressType.Donut)
Dim tsk As Task(Of Boolean) = Task.Factory.StartNew(Of Boolean)(Function()
'--Run lenghty task
Dim resu = False
Try
resu = createArticle.ProcessArticle(_artikelsAndTheirVariationsFinal)
'--Close form once done (on GUI thread)
Catch sqlex As Exception
pic.Invoke(Sub() MessageBox.Show(pic, sqlex.Message))
' pic.Invoke(Sub() MessageBox.Show(pic, ex.Message))
'pic.Invoke(Sub() TaskDialog.Show(pic, New TaskDialogInfo("Information", eTaskDialogIcon.BlueStop, "WizardPageDescriptionUberblick_BeforePageDisplayed", ex.ToString, eTaskDialogButton.Ok, eTaskDialogBackgroundColor.Blue, Nothing, Nothing, Nothing, "Jakis footer text", Nothing)))
Finally
End Try
pic.Invoke(New Action(Sub() pic.StopCircular()))
pic.Invoke(New Action(Sub() pic.Close()))
Return resu
End Function)
'--Show the form
pic.ShowDialog()
Task.WaitAll(tsk)
If tsk.Result = True Then
TaskDialog.Show(New TaskDialogInfo("Information", eTaskDialogIcon.BlueStop, "Infor", "New articel and every data has been added correctly", eTaskDialogButton.Ok, eTaskDialogBackgroundColor.Blue, Nothing, Nothing, Nothing, "Jakis footer text", Nothing))
'http://stackoverflow.com/questions/33030706/put-long-running-method-into-task-showing-new-form-meantime-and-closing-it-once
pic = New FrmCircularProgress(eCircularProgressType.Line)
Dim work As Task = Task.Factory.StartNew(Sub()
'--Run lenghty task
PrepareUberblick()
'--Close form once done (on GUI thread)
pic.Invoke(New Action(Sub() pic.StopCircular()))
pic.Invoke(New Action(Sub() pic.Close()))
End Sub)
'--Show the form
pic.ShowDialog()
Task.WaitAll(work)
If WYSWIG_Uberblick.Document IsNot Nothing Then
WYSWIG_Uberblick.Document.Write(String.Empty)
End If
'--Pobranie wszystkich html'ow wszystkich podsekcji artykulow (w tym wypadku numerów artykułów jako podsekcji) (dla sekcji Uberblick)
WYSWIG_Uberblick.DocumentText = _htmlFactory.GetAllUberblickHTML
Else
TaskDialog.Show(New TaskDialogInfo("Information", eTaskDialogIcon.NoEntry, "Infor", "Critical error occured", eTaskDialogButton.Ok, eTaskDialogBackgroundColor.Blue, Nothing, Nothing, Nothing, "Jakis footer text", Nothing))
e.Cancel = True
End If
ProcessArticle function:
Public Function ProcessArticle(artikel As ArticlesVariations) As Boolean
Dim result = True
Dim strcon = New AppSettingsReader().GetValue("ConnectionString", GetType(System.String)).ToString()
Using connection As New SqlConnection(strcon)
'-- Open generall connection for all the queries
connection.Open()
'-- Make the transaction.
Dim transaction As SqlTransaction
transaction = connection.BeginTransaction(IsolationLevel.ReadCommitted)
Dim newArticleRowId As Integer = 0
Dim articleIndex As Integer = 0
Try
For Each kvp As KeyValuePair(Of Integer, Artikel) In artikel.collection
Dim ckey As Integer = kvp.Key
articleIndex = kvp.Key 'save article key
Dim data As Artikel = kvp.Value
'-- If given article contains images list (artikel_images is a list with pictures associated with article)
If Not IsNothing(artikel.collection(articleIndex).ArtikelImages) Then
For Each img In artikel.collection(articleIndex).ArtikelImages
'--Insert article's images if exists
Using cmd As New SqlCommand("INSERT INTO T_Article_Image (Path, FK_Artikel_ID, Position) VALUES (#Path, #FK_Artikel_ID, #Position)", connection)
cmd.CommandType = CommandType.Text
cmd.Connection = connection
cmd.Transaction = transaction
cmd.Parameters.AddWithValue("#Path", img.Path)
cmd.Parameters.AddWithValue("#FK_Artikel_ID", newArticleRowId)
cmd.Parameters.AddWithValue("#Position", img.Position)
cmd.ExecuteScalar()
End Using
Next
End If
'-- If given article contains articles variations list (artikel_variation_attributes is a list with variations associated with article)
If Not IsNothing(artikel.collection(articleIndex)._artikel_variation_attributes) Then
For Each var In artikel.collection(articleIndex)._artikel_variation_attributes
'--Insert article's images if exists
Using cmd As New SqlCommand("INSERT INTO T_Artikel_T_Variation (FK_Variation_VariationAttribute_ID, FK_Artikel_ID, Position) VALUES (#FK_Variation_VariationAttribute_ID, #FK_Artikel_ID, #Position)", connection)
cmd.CommandType = CommandType.Text
cmd.Connection = connection
cmd.Transaction = transaction
cmd.Parameters.AddWithValue("#FK_Variation_VariationAttribute_ID", New Variation_VariationAttribute(var.FkVariationId, var.FkVariationAttributeId).GetId())
cmd.Parameters.AddWithValue("#FK_Artikel_ID", newArticleRowId)
cmd.Parameters.AddWithValue("#Position", var.Position)
cmd.ExecuteScalar()
End Using
Next
End If
Next
transaction.Commit()
Catch ex As Exception
result = False
'-- Roll the transaction back.
Try
transaction.Rollback()
Catch ex2 As Exception
' This catch block will handle any errors that may have occurred
' on the server that would cause the rollback to fail, such as
' a closed connection.
'Console.WriteLine("Rollback Exception Type: {0}", ex2.GetType())
'Console.WriteLine(" Message: {0}", ex2.Message)
End Try
End Try
End Using
Return result
End Function
Everything works correctly, however, when it comes to error or whatever within those methods (from our example):
Dim resu As Boolean = createArticle.ProcessArticle(_artikelsAndTheirVariationsFinal)
or this method:
PrepareUberblick()
My circural form is not closing, but it's still running (it's stuck). When I do Alt+F4 to kill my circular form, I see an error message. I assume that when an error occurs, the error message window is not going to be shown in front but it's hidden behind the circular form.
Here's the question: do you know how to fix it so when an error occurs, an error message show up in front, so user could acknowledge and then the circular form would be closed?

Answer 1

If you want to alert the user that something happened, you could show the MessageBox from your circular form, which should appear on top of it because it's generated on the same thread. You can show the MessageBox in the Catch
Try
'--Run lenghty task
resu = createArticle.ProcessArticle(_artikelsAndTheirVariationsFinal)
Catch ex As Exception
pic.Invoke(Sub() MessageBox.Show(ex.message))
End Try
'--Close form once done (on GUI thread)
pic.Invoke(New Action(Sub() pic.StopCircular()))
pic.Invoke(New Action(Sub() pic.Close()))
This way, the user will need to click OK on the MessageBox before the circular form closes.
Your whole issue stemmed from the fact that you were not calling MessageBox.Show() on the same thread that the form was created on. It's not clear from your example where the form is created, whether it's on the UI thread or not. In either case, whichever thread the form is created on must be the same one that the message box is raised on, in order for the MessageBox to be modal to the form. By calling pic.Invoke(Sub() MessageBox.Show(ex.message)), you ensure it's shown on the form's thread, and will be modal to it. You can typically force the parent window by using the overload which has
Public Shared Function Show (
owner As IWin32Window,
text As String
) As DialogResult
which would be
pic.Invoke(Sub() MessageBox.Show(pic, ex.message))
Also see:
Does MessageBox.Show() automatically marshall to the UI Thread?
Why use a owner window in MessageBox.Show?