Visual Basic

16-Mar-06 13:03

I have noticed in certain instances that updating data in a listview via a thread, is is not reflected in the UI, but the data is changed. The data is updated in a different thread using InvokeRequired ensuring thread safety. Here is a sample application:

Designer:
<global.microsoft.visualbasic.compilerservices.designergenerated()> _
Partial Class Form1
Inherits System.Windows.Forms.Form

'Form overrides dispose to clean up the component list.
<system.diagnostics.debuggernonusercode()> _
Protected Overrides Sub Dispose(ByVal disposing As Boolean)
If disposing AndAlso components IsNot Nothing Then
components.Dispose()
End If
MyBase.Dispose(disposing)
End Sub

'Required by the Windows Form Designer
Private components As System.ComponentModel.IContainer

'NOTE: The following procedure is required by the Windows Form Designer
'It can be modified using the Windows Form Designer.
'Do not modify it using the code editor.
<system.diagnostics.debuggerstepthrough()> _
Private Sub InitializeComponent()
Dim ListViewItem1 As System.Windows.Forms.ListViewItem = New System.Windows.Forms.ListViewItem(New String() {"Account1", "Inbox", ""}, -1)
Dim ListViewItem2 As System.Windows.Forms.ListViewItem = New System.Windows.Forms.ListViewItem(New String() {"Account2", "SentItems", ""}, -1)
Dim ListViewItem3 As System.Windows.Forms.ListViewItem = New System.Windows.Forms.ListViewItem(New String() {"Account3", "Help", ""}, -1)
Dim ListViewItem4 As System.Windows.Forms.ListViewItem = New System.Windows.Forms.ListViewItem(New String() {"Account4", "Save", ""}, -1)
Dim ListViewItem5 As System.Windows.Forms.ListViewItem = New System.Windows.Forms.ListViewItem(New String() {"Account5", "Drafts", ""}, -1)
Me.ListView1 = New System.Windows.Forms.ListView
Me.ColumnHeader1 = New System.Windows.Forms.ColumnHeader
Me.ColumnHeader2 = New System.Windows.Forms.ColumnHeader
Me.ColumnHeader3 = New System.Windows.Forms.ColumnHeader
Me.SuspendLayout()
'
'ListView1
'
Me.ListView1.Columns.AddRange(New System.Windows.Forms.ColumnHeader() {Me.ColumnHeader1, Me.ColumnHeader2, Me.ColumnHeader3})
Me.ListView1.FullRowSelect = True
Me.ListView1.Items.AddRange(New System.Windows.Forms.ListViewItem() {ListViewItem1, ListViewItem2, ListViewItem3, ListViewItem4, ListViewItem5})
Me.ListView1.Location = New System.Drawing.Point(12, 12)
Me.ListView1.Name = "ListView1"
Me.ListView1.Size = New System.Drawing.Size(268, 159)
Me.ListView1.TabIndex = 1
Me.ListView1.UseCompatibleStateImageBehavior = False
Me.ListView1.View = System.Windows.Forms.View.Details
'
'ColumnHeader1
'
Me.ColumnHeader1.Text = "Account"
'
'ColumnHeader2
'
Me.ColumnHeader2.Text = "Folder"
Me.ColumnHeader2.Width = 78
'
'ColumnHeader3
'
Me.ColumnHeader3.Text = "Msg"
Me.ColumnHeader3.Width = 96
'
'Form1
'
Me.AutoScaleDimensions = New System.Drawing.SizeF(6.0!, 13.0!)
Me.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font
Me.ClientSize = New System.Drawing.Size(292, 181)
Me.Controls.Add(Me.ListView1)
Me.Name = "Form1"
Me.Text = "Form1"
Me.ResumeLayout(False)

End Sub
Friend WithEvents ListView1 As System.Windows.Forms.ListView
Friend WithEvents ColumnHeader1 As System.Windows.Forms.ColumnHeader
Friend WithEvents ColumnHeader2 As System.Windows.Forms.ColumnHeader
Friend WithEvents ColumnHeader3 As System.Windows.Forms.ColumnHeader

End Class

FormCode:

Imports System
Imports System.ComponentModel
Imports System.Threading
Imports System.Windows.Forms

Public Class Form1

Delegate Sub lvwCallback(ByVal iIndex As Integer, ByVal [text] As String)

Private lCnt1 As Integer = 0, lCnt2 As Integer = 0, lCnt3 As Integer = 0
Private lMainID As Integer = Thread.CurrentThread.ManagedThreadId

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

Test.TestUpdate()

End Sub

Public Sub SetTextLvw(ByVal iIndex As Integer, ByVal [text] As String)

Debug.Print("Main:" & lMainID & "-Current:" & Thread.CurrentThread.ManagedThreadId.ToString & "-Form:" & Me.InvokeRequired & "-" & "ListView:" & Me.InvokeRequired)
If Me.ListView1.InvokeRequired Then
Dim d As New lvwCallback(AddressOf SetTextLvw)
'Me.Invoke(d, New Object() {iIndex, [text]})
Me.ListView1.Invoke(d, New Object() {iIndex, [text]})
Else
Me.ListView1.Items(iIndex).SubItems(2).Text = [text]
Debug.WriteLine("Text:" & ListView1.Items(iIndex).SubItems(0).Text & "-" & ListView1.Items(iIndex).SubItems(2).Text)
Me.ListView1.Update()
Me.ListView1.Refresh()
End If

End Sub

End Class

Public Module Test

Dim lCnt As Integer
Private oTimer As New Timers.Timer(180)

Public Sub TestUpdate()

AddHandler oTimer.Elapsed, AddressOf sTimer
oTimer.Start()

End Sub

Private Sub sTimer(ByVal sender As Object, ByVal e As System.Timers.ElapsedEventArgs)

lCnt += 1
Form1.SetTextLvw(3, "Timer:" & lCnt)

End Sub

End Module

Can anyone help?

Dave Kreskowiak17-Mar-06 1:47

17-Mar-06 1:47

mechman wrote:
Form1.SetTextLvw(3, "Timer:" & lCnt)

From your Form_Load event, you make a call to Test.TestUpdate(). The problem is that this module doesn't have any refernce to an instance of Form1. Right now, your code won't even compile. Forms do not work like they did in VB6. There is no "global" instance of Form1 that everything can see.

This is a quick and dirty hack, mostly because Modules are an outdated concept, but here's a couple of changes that should get this to work:

Public Module Test
    Public myForm As Form1
    Pricate lCnt As Integer
    Private oTimer As New Timers.Timer(180)
 
    Public Sub TestUpdate()
        If Not myForm Is Nothing Then
            Throw New Exception("You must set the value of myForm before calling TestUpdate!")
        Else
            AddHandler oTimer.Elapsed, AddressOf sTimer
            oTimer.Start()
        End If
    End Sub
 
    Private Sub sTimer(ByVal sender As Object, ByVal e As System.Timers.ElapsedEventArgs)
        lCnt += 1
        myForm.SetTextLvw(3, "Timer:" & lCnt.ToString())
    End Sub
End Module

Now, when you start your app, you have to tell this module how to get to Form1.

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    Test.myForm = Me
    Test.TestUpdate()
End Sub

RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome

mechman17-Mar-06 3:14

17-Mar-06 3:14

My aplogogies, I was trying to consolidate code at the last minute to post my real question...

The point was the listview will not update via a thread using the InvokeRequired...The value is updated if you check it via code, but the UI isn't showing the values...This was a test app to duplicate the scenerio...I have seen this several other times with the listview...I have also seen, if the ListView is not prepopulated with columns and items at design time, the InvokeRequired will not see any items or columns via code...

mechman17-Mar-06 3:17

17-Mar-06 3:17

Also, if a new thread is created with the Form's class, everything works correctly...

Dave Kreskowiak17-Mar-06 7:25

17-Mar-06 7:25

If this works, then I would suspect that your updating the control from the wrong thread...

RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome

mechman17-Mar-06 7:53

17-Mar-06 7:53

That is the problem, I know I am updating from the wrong thread, but the Invoke, InvokeRequired, etc...do not ackowledge it, so the code continues to update the data, but the UI is wrong. I can verify that it is the wrong thread by using my sample code...You can check to see if the Handle for the listview is created, and it will show it isn't...What I am seeing is very strange behavior that I don't know the workaround. I can't always gurantee my Form's class will update a control, why would you ever need class's, modules, etc. if that was the case? This is why I am posting...

Dave Kreskowiak17-Mar-06 12:37

17-Mar-06 12:37

OK. How about this...
This code assumes you have a form with a Button and a ListView on it...

    Private Delegate Sub AddItemToListViewDelegate(ByVal item As String)
    Private Delegate Sub ChangeSubItemDelegate(ByVal index As Integer, ByVal item As String)
 
    Private t1 As Thread
    Private t2 As Thread
 
    Private Const MAXITEMS As Long = 20
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        'AddItems()
        ListView1.Items.Clear()
 
        t1 = New Thread(New ThreadStart(AddressOf AddItems))
        t1.Start()
        Thread.Sleep(100)
        t2 = New Thread(New ThreadStart(AddressOf RandomSubItems))
        t2.Start()
    End Sub
 
    Private Sub AddItemToListView(ByVal item As String)
        If ListView1.InvokeRequired Then
            Dim d As New AddItemToListViewDelegate(AddressOf AddItemToListView)
            Invoke(d, New String() {item})
        Else
            Dim newItem As New ListViewItem(item)
            newItem.SubItems.Add("---")
            ListView1.Items.Add(newItem)
            Application.DoEvents()
        End If
    End Sub
 
    Private Sub ChangeSubItem(ByVal index As Integer, ByVal item As String)
        Try
            If ListView1.InvokeRequired Then
                Dim d As New ChangeSubItemDelegate(AddressOf ChangeSubItem)
                Invoke(d, New Object() {index, item})
            Else
                If ListView1.Items.Count > index Then
                    ListView1.Items(index).SubItems(1).Text = item
                    Application.DoEvents()
                End If
            End If
        Catch
        End Try
    End Sub
 
    Private Sub AddItems()
        Dim x As Long
 
        While x < MAXITEMS
            Try
                AddItemToListView(String.Format("Item #{0}", x))
                x = x + 1
            Catch ex As ThreadAbortException
                Exit While
            End Try
        End While
    End Sub
 
    Private Sub RandomSubItems()
        Dim RNG As New Random
        Dim x As Long
 
        While True
            Try
                ChangeSubItem(RNG.Next(0, MAXITEMS), RNG.Next(0, 1000).ToString())
            Catch ex As ThreadAbortException
                Exit While
            End Try
            ' This little sleep has to be in there for some reason.
            ' The form won't update properly without it!
            Thread.Sleep(1)
        End While
    End Sub
 
    Private Sub Form1_Closing(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles MyBase.Closing
        If t1 Is Nothing Then
            Exit Sub
        End If
        t1.Abort()
        t1.Join()
 
        t2.Abort()
        t2.Join()
    End Sub

RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome

mechman18-Mar-06 6:04

18-Mar-06 6:04

Now take the RandomSubItems and put it in a new Module or Class (outside of the Form's Class) and try it...the listview will not update via the UI...

Dave Kreskowiak18-Mar-06 6:24

18-Mar-06 6:24

OK. It works fine...

Form1 code:

    Private Delegate Sub AddItemToListViewDelegate(ByVal item As String)
    Private Delegate Sub ChangeSubItemDelegate(ByVal index As Integer, ByVal item As String)
 
    Private t1 As Thread
    Private t2 As Thread
 
    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Module1.myForm = Me
    End Sub
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        ListView1.Items.Clear()
        t1 = New Thread(New ThreadStart(AddressOf AddItems))
        t1.Start()
        Thread.Sleep(100)
        t2 = New Thread(New ThreadStart(AddressOf Module1.RandomSubItems))
        t2.Start()
    End Sub
 
    Private Sub AddItemToListView(ByVal item As String)
        If ListView1.InvokeRequired Then
            Dim d As New AddItemToListViewDelegate(AddressOf AddItemToListView)
            Invoke(d, New String() {item})
        Else
            Dim newItem As New ListViewItem(item)
            newItem.SubItems.Add("---")
            ListView1.Items.Add(newItem)
            Application.DoEvents()
        End If
    End Sub
 
    Public Sub ChangeSubItem(ByVal index As Integer, ByVal item As String)
        Try
            If ListView1.InvokeRequired Then
                Dim d As New ChangeSubItemDelegate(AddressOf ChangeSubItem)
                Invoke(d, New Object() {index, item})
            Else
                If ListView1.Items.Count > index Then
                    ListView1.Items(index).SubItems(1).Text = item
                    Application.DoEvents()
                End If
            End If
        Catch
        End Try
    End Sub
 
    Public Sub AddItems()
        Dim x As Long
 
        While x < MAXITEMS
            Try
                AddItemToListView(String.Format("Item #{0}", x))
                x = x + 1
            Catch ex As ThreadAbortException
                Exit While
            End Try
        End While
    End Sub
 
    Private Sub Form1_Closing(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles MyBase.Closing
        If t1 Is Nothing Then
            Exit Sub
        End If
        t1.Abort()
        t1.Join()
 
        t2.Abort()
        t2.Join()
    End Sub

Module1 code:

Imports System.Threading
 
Module Module1
    Public myForm As Form1
    Public Const MAXITEMS As Long = 20
 
    Public Sub RandomSubItems()
        Dim RNG As New Random
        Dim x As Long
 
        While True
            Try
                myForm.ChangeSubItem(RNG.Next(0, MAXITEMS), RNG.Next(0, 1000).ToString())
            Catch ex As ThreadAbortException
                Exit While
            End Try
            Thread.Sleep(1)
        End While
    End Sub
End Module

I never use Modules, ... ever. They're an outdated concept that's around just to be backwards-compatible with VB6 code.

RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome

mechman19-Mar-06 7:30

19-Mar-06 7:30

Thanks Dave for all your help...I was simply trying to duplicate my issue in a easy manor...The problem was, in the module or Class (what I really use) I reference the form itself and not the public variable you used in the module:

Public myForm As Form1

Change
myForm.ChangeSubItem(RNG.Next(0, MAXITEMS), RNG.Next(0, 1000).ToString())
To
Form1.ChangeSubItem(RNG.Next(0, MAXITEMS), RNG.Next(0, 1000).ToString())

and you see the issue...changing back to what you had corrects it...Thanks again...

Can you tell why it was needed, just curious?

Dave Kreskowiak19-Mar-06 14:22

19-Mar-06 14:22

Because in that Module, or any other class, Form1 doesn't exist. This is not like VB6 where the forms existed in every context. The is REAL Object Oriented Programming and you have to follow the rules this time.

RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome

mechman19-Mar-06 14:27

19-Mar-06 14:27

Ok...how come you can call Form1 directly, cheating the threading model? Just trying to get the full understanding...

Dave Kreskowiak19-Mar-06 16:51

19-Mar-06 16:51

I don't call Form1 directly anywhere. What are you talking about?? A little snippet would help...

RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome

mechman19-Mar-06 18:05

19-Mar-06 18:05

If you pass a ListViewItem to the module, and reference the form and listview object (to update it), you can update the the ListViewItem..I guess I have answered my own question because it does the same as the myForm object, just using a different object (lower level)...

Dave Kreskowiak20-Mar-06 2:48