How do you pass a reference of the Form when calling a EnumWindows

I'm trying to Write to a ListBox Form during a EnumWindows Call Back.

My research point towards using a reference/pointer to access the Form from the Call Back

Below is a copy of the code is below.

###### Module Code:
Module Module1

    Public Delegate Function EnumWindowsProc(ByVal hwnd As IntPtr, ByVal lParam As Int32) As Int32

    Public Declare Function EnumWindows Lib "user32.dll" _
            (ByVal lpEnumFunc As EnumWindowsProc, ByVal lParam As Int32) As Int32

    Public Declare Function GetWindowTextLength Lib "user32.dll" Alias "GetWindowTextLengthA" _
        (ByVal hwnd As IntPtr) As Int32

    Public Declare Function GetWindowText Lib "user32.dll" Alias "GetWindowTextA" _
        (ByVal hwnd As IntPtr, ByVal lpString As String, ByVal cch As Int32) As Int32

    'Callback function to enum windows
    Public Function EnumWindowsCallBack(ByVal hwnd As IntPtr, ByVal lParam As Int32) As Int32
        Dim sSave As String

        'Get the windowtext length
        sSave = Space(GetWindowTextLength(hwnd) + 1)

        'get the window text
        GetWindowText(hwnd, sSave, Len(sSave))

        'remove the last Chr(0)
        sSave = Microsoft.VisualBasic.Left(sSave, Len(sSave) - 1)

        'Error below: Reference to a non-shared member requires an Object Reference
        Form1.ListBox1.Items.Add(sSave)


        If sSave.Trim <> "" Then
            Debug.WriteLine(sSave)
        End If

        Return 1 'continue enumeration        
    End Function

End Module

###### Form Code:

Public Class Form1
    Inherits System.Windows.Forms.Form

#Region " Windows Form Designer generated code "

    Public Sub New()
        MyBase.New()

        'This call is required by the Windows Form Designer.
        InitializeComponent()

        'Add any initialization after the InitializeComponent() call

    End Sub

    'Form overrides dispose to clean up the component list.
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then
            If Not (components Is Nothing) Then
                components.Dispose()
            End If
        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.
    Public WithEvents ListBox1 As System.Windows.Forms.ListBox
    Public WithEvents Button1 As System.Windows.Forms.Button
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
        Me.Button1 = New System.Windows.Forms.Button()
        Me.ListBox1 = New System.Windows.Forms.ListBox()
        Me.SuspendLayout()
        '
        'Button1
        '
        Me.Button1.Location = New System.Drawing.Point(40, 184)
        Me.Button1.Name = "Button1"
        Me.Button1.Size = New System.Drawing.Size(200, 56)
        Me.Button1.TabIndex = 0
        Me.Button1.Text = "Button1"
        '
        'ListBox1
        '
        Me.ListBox1.Location = New System.Drawing.Point(32, 24)
        Me.ListBox1.Name = "ListBox1"
        Me.ListBox1.Size = New System.Drawing.Size(216, 134)
        Me.ListBox1.TabIndex = 1
        '
        'Form1
        '
        Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
        Me.ClientSize = New System.Drawing.Size(292, 273)
        Me.Controls.AddRange(New System.Windows.Forms.Control() {Me.ListBox1, Me.Button1})
        Me.Name = "Form1"
        Me.Text = "Form1"
        Me.ResumeLayout(False)

    End Sub

#End Region


    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        EnumWindows(AddressOf EnumWindowsCallBack, 0)
    End Sub

    Public Sub AddProcess(ByVal strName As String)
        Me.ListBox1.Items.Add(strName)
    End Sub

    ' Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    '
    '  End Sub
End Class
LVL 1
vaultworldAsked:
Who is Participating?
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

arif_eqbalCommented:
Declare a variabl at Module Level

Public Lst as ListBox

Then on the form on Button Click you are writing

 Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        EnumWindows(AddressOf EnumWindowsCallBack, 0)
    End Sub

Now add one more line before call to EnumWindows

 Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Lst=ListBox1      '--------> ADD THIS LINE
        EnumWindows(AddressOf EnumWindowsCallBack, 0)
    End Sub

Then in the EnumWindows function

'Error below: Reference to a non-shared member requires an Object Reference
        Form1.ListBox1.Items.Add(sSave)

instead of this line use

    Lst.Items.Add(sSave)
0

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
vaultworldAuthor Commented:
Here's the Final Answer

Thanks for all the help.

Public Class Form1
    Inherits System.Windows.Forms.Form

#Region " Windows Form Designer generated code "

    Public Sub New()
        MyBase.New()

        'This call is required by the Windows Form Designer.
        InitializeComponent()

        'Add any initialization after the InitializeComponent() call

    End Sub

    'Form overrides dispose to clean up the component list.
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then
            If Not (components Is Nothing) Then
                components.Dispose()
            End If
        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.
    Friend WithEvents ListBox1 As System.Windows.Forms.ListBox
    Friend WithEvents Button1 As System.Windows.Forms.Button
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
        Me.ListBox1 = New System.Windows.Forms.ListBox()
        Me.Button1 = New System.Windows.Forms.Button()
        Me.SuspendLayout()
        '
        'ListBox1
        '
        Me.ListBox1.Location = New System.Drawing.Point(32, 16)
        Me.ListBox1.Name = "ListBox1"
        Me.ListBox1.Size = New System.Drawing.Size(240, 147)
        Me.ListBox1.TabIndex = 0
        '
        'Button1
        '
        Me.Button1.Location = New System.Drawing.Point(32, 200)
        Me.Button1.Name = "Button1"
        Me.Button1.Size = New System.Drawing.Size(240, 64)
        Me.Button1.TabIndex = 1
        Me.Button1.Text = "Button1"
        '
        'Form1
        '
        Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
        Me.ClientSize = New System.Drawing.Size(292, 273)
        Me.Controls.AddRange(New System.Windows.Forms.Control() {Me.Button1, Me.ListBox1})
        Me.Name = "Form1"
        Me.Text = "Form1"
        Me.ResumeLayout(False)

    End Sub

#End Region

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Lst = ListBox1
        EnumWindows(AddressOf EnumWindowsCallBack, 0)
    End Sub

End Class

Module Module1

    Public Lst As ListBox

    Public Delegate Function EnumWindowsProc(ByVal hwnd As IntPtr, ByVal lParam As Int32) As Int32

    Public Declare Function EnumWindows Lib "user32.dll" _
            (ByVal lpEnumFunc As EnumWindowsProc, ByVal lParam As Int32) As Int32

    Public Declare Function GetWindowTextLength Lib "user32.dll" Alias "GetWindowTextLengthA" _
        (ByVal hwnd As IntPtr) As Int32

    Public Declare Function GetWindowText Lib "user32.dll" Alias "GetWindowTextA" _
        (ByVal hwnd As IntPtr, ByVal lpString As String, ByVal cch As Int32) As Int32

    'Callback function to enum windows
    Public Function EnumWindowsCallBack(ByVal hwnd As IntPtr, ByVal lParam As Int32) As Int32
        Dim sSave As String

        'Get the windowtext length
        sSave = Space(GetWindowTextLength(hwnd) + 1)

        'get the window text
        GetWindowText(hwnd, sSave, Len(sSave))

        'remove the last Chr(0)
        sSave = Microsoft.VisualBasic.Left(sSave, Len(sSave) - 1)

        'Error below: Reference to a non-shared member requires an Object Reference
        Lst.Items.Add(sSave)


        If sSave.Trim <> "" Then
            Debug.WriteLine(sSave)
        End If

        Return 1 'continue enumeration        
    End Function

End Module
0
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Visual Basic.NET

From novice to tech pro — start learning today.

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.