[VB6] ThunderMain class

This is a class that exposes only one property - ThunderMain's hWnd. ThunderMain's hWnd is chiefly useful in subclassing. It obtains that handle in one of two ways - the first is through the GetWindow function and the second is via the EnumThreadWindows/EnumThreadWndProc functions. The self-contained callback procedure was made possible by Merri's Streamlined SelfCallback code snippets. The algorithm for retrieving the handle is based on samples by Karl E. Peterson. A demo project is included in the zip file.

This is a more lightweight version of the previous class.

Code:

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'clsThunderMainLite.cls

Option Explicit    'Retrieves the handle of the unseen top-level window in a VB process.

#If False Then
Private Const sThunderMain As String = "ThunderRT5Main"    'VB5
#Else                                                              'Set this accordingly
Private Const sThunderMain As String = "ThunderRT6Main"    'VB6
#End If

Private Const GW_OWNER As Long = 4    'The retrieved handle identifies the specified window's owner window, if any.

Private Type UUID
    Data1    As Long
    Data2    As Integer
    Data3    As Integer
    Data4(7) As Byte
End Type

Private Declare Function FindWindowW Lib "user32.dll" (Optional ByVal lpClassName As Long, Optional ByVal lpWindowName As Long) As Long
Private Declare Function GetWindow Lib "user32.dll" (ByVal hWnd As Long, ByVal uCmd As Long) As Long
Private Declare Function StringFromGUID2 Lib "ole32.dll" (ByRef rguid As UUID, ByVal lpsz As Long, ByVal cchMax As Long) As Long
Private Declare Function SysReAllocStringLen Lib "oleaut32.dll" (ByVal pBSTR As Long, Optional ByVal pszStrPtr As Long, Optional ByVal Length As Long) As Long
Private Declare Function UuidCreate Lib "rpcrt4.dll" (ByRef lpUuid As UUID) As Long

Private m_hWnd As Long

Private Sub Class_Initialize()
    Dim sPrevTitle As String

    If Forms.Count Then                                                'If there are any loaded Forms,
        m_hWnd = GetWindow(Forms(0&).hWnd, GW_OWNER)                    'retrieve ThunderMain's hWnd directly
        Exit Sub                                                        'by getting their owner window's handle
    End If                                                              '(ThunderMain owns all Forms in any project)

    With App
        sPrevTitle = .Title                                            'Save ThunderMain's current window text
      .Title = CreateGUID                                              'Change title to a highly unique string
        If Not InIDE Then                                              'The class name differs slightly in & out of IDE
            m_hWnd = FindWindowW(StrPtr(sThunderMain), StrPtr(.Title))  'Search for the window handle,
        Else                                                            'specifying the different class names
            m_hWnd = FindWindowW(StrPtr("ThunderMain"), StrPtr(.Title)) 'and the new unique window text
        End If
      .Title = sPrevTitle                                              'Restore the previous title
    End With
End Sub

Public Property Get hWnd() As Long                                      'Returns ThunderMain's window handle
    hWnd = m_hWnd
End Property

Private Function CreateGUID() As String                                'Smallest but fastest GUID generator
    Const RPC_S_OK = 0&: Dim udtUUID As UUID

    If UuidCreate(udtUUID) = RPC_S_OK Then _
    SysReAllocStringLen VarPtr(CreateGUID), , 38&: _
    StringFromGUID2 udtUUID, StrPtr(CreateGUID), 39&
End Function

Private Function InIDE(Optional ByRef B As Boolean = True) As Boolean  'Very efficient function for testing whether
    If B Then Debug.Assert Not InIDE(InIDE) Else B = True              'this code is running in the IDE or compiled
End Function                                                            'Based on the original by Vesa Piittinen




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One situation where ThunderMain's hWnd is useful is when assigning a new Alt-Tab window icon to the app^†. For example:

Code:

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Option Explicit

Private Const ICON_BIG  As Long = 1
Private Const ICON_SMALL As Long = 0
Private Const WM_SETICON As Long = &H80

Private Declare Function LoadIconW Lib "user32.dll" (ByVal hInstance As Long, ByVal lpIconName As Long) As Long
Private Declare Function SendMessageW Lib "user32.dll" (ByVal hWnd As Long, ByVal uMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long

Private Sub Form_Load()
    Dim hIcon As Long

    hIcon = LoadIconW(App.hInstance, 101&)

    With New clsThunderMainLite                          'This sets the icon used
        SendMessageW .hWnd, WM_SETICON, ICON_BIG, hIcon  'in the Alt-Tab window and the
        SendMessageW .hWnd, WM_SETICON, ICON_SMALL, hIcon 'Applications tab of Task Manager
    End With
End Sub


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^†Worked only in XP; no longer applies to Win 7.