Using CreateDialog in VBA in an Attempt to Create Modeless Dialog Boxes

This can be made to work, although if you should try to make it work is another question. I have a working version that shows an empty dialog. I don’t have any more time tonight to finish with actual controls on the dialog, but I’m posting in the hope it’ll get you started.

First you need to forget about CreateDialog because they require the dialog template to be in the resource section. You can use CreateDialogIndirectParam to create a dialog from an in-memory dialog template. You will need this:

Private Type DLGTEMPLATE
    style As Long
    dwExtendedStyle As Long
    cdit As Integer
    x As Integer
    y As Integer
    cx As Integer
    cy As Integer
End Type

Private Type DLGITEMTEMPLATE
    style As Long
    dwExtendedStyle As Long
    x As Integer
    y As Integer
    cx As Integer
    cy As Integer
    id As Integer
End Type

Private Type DLG
    dlgtemp As dlgtemplate
    menu As Long
    classname As String
    title As String
End Type

Private Declare PtrSafe Function CreateDialogIndirectParam Lib "User32.dll" Alias "CreateDialogIndirectParamW" _
  (ByVal hInstance As Long, _
  ByRef lpTemplate As DLGTEMPLATE, _
  ByVal hWndParent As Long, _
  ByVal lpDialogFunc As LongPtr, _
  ByVal lParamInit As Long) _
  As LongPtr

Const WM_INITDIALOG As Long = &H110
Const DS_CENTER As Long = &H800&
Const DS_SETFONT As Long = &H40
Const DS_MODALFRAME As Long = &H80
Const WS_EX_APPWINDOW As Long = &H40000

Then call it like this:

Dim d As DLG
d.dlgtemp.style = DS_MODALFRAME + WS_POPUP + WS_VISIBLE + WS_CAPTION + WS_SYSMENU
d.dlgtemp.dwExtendedStyle = WS_EX_APPWINDOW
d.dlgtemp.cdit = 0
d.dlgtemp.x = 100
d.dlgtemp.y = 100
d.dlgtemp.cx = 200
d.dlgtemp.cy = 200
d.menu = 0
d.title = "Test"
d.classname = "Test"

CreateDialogIndirectParam 0, d.dlgtemp, 0, AddressOf DlgFunc, 0

with DlgFunc looking something like this:

Public Function DlgFunc(ByVal hwndDlg As LongPtr, ByVal uMsg As LongPtr, ByVal wParam As LongPtr, ByVal lParam As LongPtr) As LongPtr
    If uMsg = h110 Then  ' = WM_INITDIALOG - you should make a const for the various window messages you'll need...
        DlgFunc = True
    Else
        DlgFunc = False
    End If
End Function

It’s been over a decade since I last did any of this stuff. But if you’re determined to go this route, I think this approach is the most promising – the next step is to adapt the DLG struct to add some DLGITEMTEMPLATE members, set d.dlgtemp.cdit to the number of controls on your dialog, and start handling control messages in your DlgFunc.