How to get header item in wndproc listview

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ListView

Hi
I'm trying to make my own header draw.
So far it's working but I can't find the internal ID from the header.

What I have tried:

Dim pnmhdr = CType(m.GetLParam(GetType(NMHDR)), NMHDR)
                If pnmhdr.code = NM_CUSTOMDRAW Then
                    Dim pnmlv = CType(m.GetLParam(GetType(NMLVCUSTOMDRAW)), NMLVCUSTOMDRAW)
                    Select Case pnmlv.nmcd.dwDrawStage
                        Case CDDS.CDDS_PREPAINT
                            If (pnmlv.dwItemType = LVCDI_GROUP) Then
                                Dim rectHeader As New RECT With {
                                    .top = LVGGR_HEADER
                                }
                                Dim rectGroep As New RECT With {
                                    .top = LVGGR_GROUP
                                    }
                                Dim nItem = CInt(pnmlv.nmcd.dwItemSpec)

But Item gives me a number higher that the number of groups. It looks like after removeing groups the counter keeps counting from the same number. and not restarting from zero.

So the question is how do I find the real ID

Jan