Delegates and Classes

[Dave]

Good morning,

I have a class that must trigger an event in a module, which will in
turn update a Label on a form. Due to being in a seperate thread,I
must use a delegate.

Now here is my question. I have managed to create a delegate on a
Form using the Invoke method. In this case though, the class is
actually created as a global variable and it's instance is created in
a module.

What is the best way to implement this delegate since I can't perform
an Invoke from a module?

Thanks for the help,

Dave

[Dave]

Re: Delegates and Classes

I have attached a copy of the code at module end:

Module modSystemMonito r
Public Delegate Sub MyDelegate(ByVa l intIndex As Integer)

Public frmOver As frmOverview
Public colSystem As New Collection
Public MyDel As MyDelegate

Public Sub LoadSystemId()
Dim n As Integer
Dim Dave As clsSystem
MyDel = AddressOf MyDelegateSub
n = 1
Dave = New clsSystem("Loca l Test", "Local Test", "WSDEV",
"MONITOR")
AddHandler Dave.DataAvaila bleEvent, AddressOf
colSystem_NewDa taAvailable
Dave.Index = n
colSystem.Add(D ave, Dave.SystemID)
n = 2
Dave = New clsSystem("Back up Domain Controller", "Backup Domain
Controller", "MSS06", "MONITOR")
AddHandler Dave.DataAvaila bleEvent, AddressOf
colSystem_NewDa taAvailable
Dave.Index = n
colSystem.Add(D ave, Dave.SystemID)
End Sub

'************** *************** ****
Public Sub MyDelegateSub(B yVal intIndex As Integer)
frmOver.Label2. Text = "Testing123 |" & intIndex

'*** <<This is where I get the Error Cross-Thread Operation Not Valid:
Control 'Label2' accessed form a thread other than the thread it was
created in > *****

End Sub
'************** *************** ****

Private Sub colSystem_NewDa taAvailable(ByV al intIndex As Integer)
Dim Dave As New Data.DataTable
Try
MyDel.Invoke(in tIndex)
MsgBox(intIndex )
Catch
MsgBox(Err.Desc ription)
End Try
End Sub
End Module


On Wed, 03 Jan 2007 09:22:52 -0500, Dave <Dave@Canada.co mwrote:

>Good morning,
>
>I have a class that must trigger an event in a module, which will in
>turn update a Label on a form. Due to being in a seperate thread,I
>must use a delegate.
>
>Now here is my question. I have managed to create a delegate on a
>Form using the Invoke method. In this case though, the class is
>actually created as a global variable and it's instance is created in
>a module.
>
>What is the best way to implement this delegate since I can't perform
>an Invoke from a module?
>
>Thanks for the help,
>
>Dave

[Herfried K. Wagner [MVP]]

Re: Delegates and Classes

Dave,

"Dave" <Dave@Canada.co mschrieb:

Module modSystemMonito r
Public Delegate Sub MyDelegate(ByVa l intIndex As Integer)
>
Public frmOver As frmOverview
Public colSystem As New Collection
Public MyDel As MyDelegate
>
Public Sub LoadSystemId()
Dim n As Integer
Dim Dave As clsSystem
MyDel = AddressOf MyDelegateSub
n = 1
Dave = New clsSystem("Loca l Test", "Local Test", "WSDEV",
"MONITOR")
AddHandler Dave.DataAvaila bleEvent, AddressOf
colSystem_NewDa taAvailable
Dave.Index = n
colSystem.Add(D ave, Dave.SystemID)
n = 2
Dave = New clsSystem("Back up Domain Controller", "Backup Domain
Controller", "MSS06", "MONITOR")
AddHandler Dave.DataAvaila bleEvent, AddressOf
colSystem_NewDa taAvailable
Dave.Index = n
colSystem.Add(D ave, Dave.SystemID)
End Sub
>
'************** *************** ****
Public Sub MyDelegateSub(B yVal intIndex As Integer)
frmOver.Label2. Text = "Testing123 |" & intIndex
>
'*** <<This is where I get the Error Cross-Thread Operation Not Valid:
Control 'Label2' accessed form a thread other than the thread it was
created in > *****

\\\
Private m_Text As String

Public Sub MyDelegateSub(B yVal intIndex As Integer)
m_Text = "Testing123 |" & intIndex
If frmOver.Label2. InvokeRequired Then
frmOver.Label2. Invoke(CType(Ad dressOf SetText, MethodInvoker))
Else
SetText()
End If
End Sub

Private Sub SetText()
frmOver.Label2. Text = m_Text
End Sub
///

--
M S Herfried K. Wagner
M V P <URL:http://dotnet.mvps.org/>
V B <URL:http://dotnet.mvps.org/dotnet/faqs/>

[Dave]

Re: Delegates and Classes

Hi Herfriend,

Thanks for the help, but still no success. The application freezes on
the Label2.Invoke method.

Here is the complete source. Every 3 seconds a ping is sent out to a
host, the ping response (good or bad) forces an Invoke. The idea is
to eventually pass a table with the latest pings.

I have looked through all of the web examples and this delege should
work, but doesn't. I've tried about 8 different ways with no success.

Thanks again.

////
Module modSystemMonito r
Public Dave As clsSystem
Public frmOver As frmOverview
Public Sub LoadSystemId()
Dim n As Integer
n = 1
Dave = New clsSystem("Loca l Test", "Local Test", "WSDEV",
"MONITOR")
Dave.Index = n
If frmOver Is Nothing Then
frmOver = New frmOverview
frmOver.Height = frmMain.SplitCo ntainer2.Panel2 .Height
frmOver.Width = frmMain.SplitCo ntainer2.Panel2 .Width
frmOver.TopLeve l = False
frmOver.Parent = frmMain.SplitCo ntainer2.Panel2
frmOver.Show()
frmOver.Anchor = AnchorStyles.Le ft Or AnchorStyles.Ri ght
End If
frmOver.Label1. Text = "Overview"
frmOver.BringTo Front()
End Sub
End Module

Public Class frmOverview
Private m_Text As String
Private Sub frmOverview_Loa d(ByVal sender As System.Object, ByVal e
As System.EventArg s) Handles MyBase.Load
Dave.NotifyOnDa taChange(New
clsSystem.Deleg ateDataChanged( AddressOf MyDelegateSub))
End Sub
Private Sub MyDelegateSub(B yVal intIndex As Integer)
m_Text = "Received Something:" & Now & ":" & intIndex
If frmOver.Label2. InvokeRequired Then
MsgBox("Must Invoke:" & intIndex)
frmOver.Label2. Invoke(CType(Ad dressOf SetText, MethodInvoker))
Else
SetText()
End If
End Sub
Private Sub SetText()
Label2.Text = m_Text
End Sub

Imports nsoftware.IPWor ks
Public Class clsSystem
Public Delegate Sub DelegateDataCha nged(ByVal intIndex As Integer)
Private DataChanged As DelegateDataCha nged
Private WithEvents timerPing As New Timer
Private WithEvents pingSystem As New nsoftware.IPWor ks.Ping
Private mintIndex As Integer
Public Structure custSystemList
Public strSystemID As String
Public strDescription As String
Public strHost As String
Public strSystemType As String
End Structure
Private SystemList As custSystemList
Private PingHistory As New Data.DataTable
Public Sub New(ByVal strSystemID As String, ByVal strDescription As
String, ByVal strHost As String, ByVal strSystemType As String)
Dim DateTime As New Data.DataColumn ("DateTime")
Dim PingResult As New Data.DataColumn ("PingResult ")
DateTime.DataTy pe = System.Type.Get Type("System.Da teTime")
PingResult.Data Type = System.Type.Get Type("System.St ring")
PingHistory.Col umns.Add(DateTi me)
PingHistory.Col umns.Add(PingRe sult)
SystemList.strS ystemID = strSystemID
SystemList.strD escription = strDescription
SystemList.strH ost = strHost
SystemList.strS ystemType = strSystemType
timerPing.Inter val = 3000
timerPing.Enabl ed = True
pingSystem.Time out = 1
End Sub
Public Sub NotifyOnDataCha nge(ByVal value As DelegateDataCha nged)
DataChanged = value
End Sub
Public Sub AddPingHistory( ByVal strDateTime As DateTime, ByVal
strPingResult As String)
PingHistory.Row s.Add()
PingHistory.Row s(PingHistory.R ows.Count - 1).Item("DateTi me") =
strDateTime
PingHistory.Row s(PingHistory.R ows.Count - 1).Item("PingRe sult") =
strPingResult
If PingHistory.Row s.Count 10 Then
PingHistory.Row s.Remove(PingHi story.Rows(0))
End If
DataChanged.Inv oke(mintIndex)
End Sub
Public Function GetPingHistory( ) As Data.DataTable
GetPingHistory = PingHistory
End Function
Public Property Description()
Get
Description = SystemList.strD escription
End Get
Set(ByVal value)

End Set
End Property
Public Property Host()
Get
Host = SystemList.strH ost
End Get
Set(ByVal value)

End Set
End Property
Public Property Index()
Get
Index = mintIndex
End Get
Set(ByVal value)
mintIndex = value
End Set
End Property
Public Property SystemID()
Get
SystemID = SystemList.strS ystemID
End Get
Set(ByVal value)

End Set
End Property
Public Property SystemType()
Get
SystemType = SystemList.strS ystemType
End Get
Set(ByVal value)

End Set
End Property
Private Sub timerPing_Tick( ByVal sender As Object, ByVal e As
System.EventArg s) Handles timerPing.Tick
pingSystem.Ping Host(SystemList .strHost)
End Sub
Private Sub pingSystem_OnEr ror(ByVal sender As Object, ByVal e As
nsoftware.IPWor ks.PingErrorEve ntArgs) Handles pingSystem.OnEr ror
AddPingHistory( Now, e.Description)
End Sub
Private Sub pingSystem_OnRe sponse(ByVal sender As Object, ByVal e As
nsoftware.IPWor ks.PingResponse EventArgs) Handles pingSystem.OnRe sponse
AddPingHistory( Now, "Ping Responded in " & e.ResponseTime & "ms")
End Sub
End Class
\\\

[Branco Medeiros]

Re: Delegates and Classes


Dave wrote:
<snip>

Thanks for the help, but still no success. The application freezes on
the Label2.Invoke method.
>
Here is the complete source. Every 3 seconds a ping is sent out to a
host, the ping response (good or bad) forces an Invoke. The idea is
to eventually pass a table with the latest pings.
>
I have looked through all of the web examples and this delege should
work, but doesn't. I've tried about 8 different ways with no success.

<snip>

I tried to reproduce your scenario here and it worked without apparent
problems (notice that in my setup I just created a RunTest method in
clsSystem that would call AddPingHistory at random from a separate
thread).

Just to state that I didn't speak of flowers (as an old saying goes,
here), let me suggest you a couple of changes:

In clsSystem, it would be safe to test the delegate before Invoking:

If DataChanged IsNot Nothing Then DataChanged.Inv oke(mintIndex)

Also, I made some cosmectic changes in frmOverview:

Private Sub MyDelegateSub(B yVal intIndex As Integer)
m_Text = "Received Something:" & Now & ":" & intIndex
SetText()
End Sub

Private Sub SetText()
Static Handler As MethodInvoker = AddressOf SetText
If InvokeRequired Then
Invoke(Handler)
Else
Label2.Text = m_Text
End If
End Sub

As you can see, the test for InvokeRequired is placed in SetText, I
suppose it simplyfies the coding of other methods that would need to
call SetText from other threads. But, as I said before, this is mostly
cosmectic, as your original code seems to be working (thread-wise).

Regards,

Branco.