Handle clicks to custom buttons in the System Menu

Question

I've managed to create a Class that allows me to add an 'About...' button to the System Menu of any form. This part works fine, with the button being added by the load event of the form, but how do I handle clicks of that button? Thanks.

Here is how I'm adding the button -

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

    {More code....}
    Dim SysMenu = New SystemMenu(Me)
    {More code....}

End Sub

And here is the SystemMenu class -

Imports System.Windows.Forms

Public Class SystemMenu

    Private Declare Function GetSystemMenu Lib "user32" (ByVal hWnd As IntPtr, ByVal bRevert As Boolean) As IntPtr
    Private Declare Function AppendMenu Lib "user32" Alias "AppendMenuA" (ByVal hMenu As IntPtr, ByVal uFlags As Int32, ByVal uIDNewItem As IntPtr, ByVal lpNewItem As String) As Boolean
    Private Const MF_STRING As Integer = &H0
    Private Const MF_SEPARATOR As Integer = &H800

    Private m_hSysMenu As IntPtr
    Private Property hSysMenu() As IntPtr
        Get
            Return Me.m_hSysMenu
        End Get
        Set(ByVal Value As IntPtr)
            Me.m_hSysMenu = Value
        End Set
    End Property

    '**
    ' Constructor
    '*
    Protected Friend Sub New(ByRef Form As Form)
        Me.hSysMenu = GetSystemMenu(Form.Handle, False)
        AddAbout(Form)
    End Sub

    '**
    ' Add an 'About' button to the system menu of the given form
    '*
    Private Sub AddAbout(ByRef Form As Form)
        AppendMenu(Me.hSysMenu, MF_SEPARATOR, 1000, Nothing)
        AppendMenu(Me.hSysMenu, MF_STRING, 1001, "About...")
    End Sub

End Class

Answer 1

Check this out. Add the SubclassedSystemMenu.vb file to the project and add this to your main form

Private WithEvents sysMenu As SubclassedSystemMenu

Protected Overrides Sub OnLoad(e As System.EventArgs)
  sysMenu = New SubclassedSystemMenu(Me.Handle.ToInt32, "&About...")
End Sub

And then subscribe to its LaunchDialog event and open the form

Private Sub sysMenu_LaunchDialog() Handles sysMenu.LaunchDialog
  Dim f as New frmAbout
  f.ShowDialog(Me)
End Sub

And here is the SubclassedSystemMenu class

Public Class SubclassedSystemMenu
Inherits System.Windows.Forms.NativeWindow
Implements IDisposable

Private Declare Function GetSystemMenu Lib "user32" (ByVal hwnd As Int32, _
                                                     ByVal bRevert As Boolean) As Int32

Private Declare Function AppendMenu Lib "user32" Alias "AppendMenuA" (ByVal hMenu As Int32, _
                                                                      ByVal wFlags As Int32, _
                                                                      ByVal wIDNewItem As Int32, _
                                                                      ByVal lpNewItem As String) As Int32

Private Const MF_STRING As Int32 = &H0       ' Menu string format
Private Const MF_SEPARATOR As Int32 = &H800  ' Menu separator
Private Const WM_SYSCOMMAND As Int32 = &H112 ' System menu 
Private Const ID_ABOUT As Int32 = 1000       ' Our ID for the new menu item

Private mintSystemMenu As Int32 = 0                 ' Parent system menu handle
Private mintHandle As Int32 = 0                     ' Local parent window handle
Private mstrMenuItemText As String = String.Empty   ' New menu item text

Public Event LaunchDialog()

Public Sub New(ByVal intWindowHandle As Int32, _
               ByVal strMenuItemText As String)

    Me.AssignHandle(New IntPtr(intWindowHandle))

    mintHandle = intWindowHandle
    mstrMenuItemText = strMenuItemText

    ' Retrieve the system menu handle
    mintSystemMenu = GetSystemMenu(mintHandle, 0)

    If AddNewSystemMenuItem() = False Then
        Throw New Exception("Unable to add new system menu items")
    End If

End Sub

Protected Overrides Sub WndProc(ByRef m As System.Windows.Forms.Message)

    Select Case m.Msg
        Case WM_SYSCOMMAND

            MyBase.WndProc(m)

            If m.WParam.ToInt32 = ID_ABOUT Then
                If mintSystemMenu <> 0 Then
                    RaiseEvent LaunchDialog()
                End If
            End If

        Case Else
            MyBase.WndProc(m)
    End Select

End Sub

Public Sub Dispose() Implements System.IDisposable.Dispose

    If Not Me.Handle.Equals(IntPtr.Zero) Then
        Me.ReleaseHandle()
    End If

End Sub

Private Function AddNewSystemMenuItem() As Boolean
    Try
        ' Append the extra system menu items
        Return AppendToSystemMenu(mintSystemMenu, mstrMenuItemText)

    Catch ex As Exception
        Return False
    End Try
End Function

Private Function AppendToSystemMenu(ByVal intHandle As Int32, _
                                    ByVal strText As String) As Boolean

    Try
        ' Add the seperator menu item
        Dim intRet As Int32 = AppendMenu(intHandle, MF_SEPARATOR, 0, String.Empty)

        ' Add the About... menu item
        intRet = AppendMenu(intHandle, MF_STRING, ID_ABOUT, strText)

        If intRet = 1 Then
            Return True
        Else
            Return False
        End If

    Catch ex As Exception
        Return False
    End Try
End Function

End Class