Subclassing ComboBox

[gmichaud]

Hello,

I'm trying to subclass the ComboBox control so that I can process WM_MOUSEMOVE message. It seems that the WM_MOUSEMOVE messages are only sent to the child TextBox inside the combo, so I need to do FindWindowEx() first to get the handle.

I am getting a strange bug. If I subclass the combo box, it works fine. If I subclass the child text box, VB seems to get in an infinite loop and crash very fast (invalid page fault).

If anyone has any solution or any alternatives to getting mouse movement info for this control let me know.

Best regards,
Gabriel

[Aaron Young]

Why do you want to Trap the WM_MOUSEMOVE Message? To Get the ListItem as it's selected?

Try this:'In a Module..
private Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (byval hwnd as Long, byval nIndex as Long, byval dwNewLong as Long) as Long
private Declare Function CallWindowProc Lib "user32" Alias "CallWindowProcA" (byval lpPrevWndFunc as Long, byval hwnd as Long, byval Msg as Long, byval wParam as Long, byval lParam as Long) as Long
private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (byval hwnd as Long, byval wMsg as Long, byval wParam as Long, lParam as Any) as Long

private Const GWL_WNDPROC = (-4)
private Const WM_CTLCOLORLISTBOX = &H134
private Const LB_GETCURSEL = &H188

private lPrevWndFunc as Long
public oLabel as Label

private Function WindowProc(byval hwnd as Long, byval Msg as Long, byval wParam as Long, byval lParam as Long) as Long
Dim iIndex as Long

If Msg = WM_CTLCOLORLISTBOX then
iIndex = SendMessage(lParam, LB_GETCURSEL, 0&, byval 0&)
If iIndex >= 0 then oLabel = "Item Index: " & iIndex
End If
WindowProc = CallWindowProc(lPrevWndFunc, hwnd, Msg, wParam, lParam)
End Function

public Sub SubClassIt(byval hwnd as Long, byval Add as Boolean)
If Add then
lPrevWndFunc = SetWindowLong(hwnd, GWL_WNDPROC, AddressOf WindowProc)
else
Call SetWindowLong(hwnd, GWL_WNDPROC, lPrevWndFunc)
End If
End Sub

'In a Form, with a Label and a ComboBox..
private Sub Form_Load()
Dim iIndex as Long
set oLabel = Label1
SubClassIt Combo1.hwnd, true
for iIndex = 1 to 10
Combo1.AddItem "Item " & iIndex
next
End Sub

private Sub Form_Unload(Cancel as Integer)
SubClassIt Combo1.hwnd, false
End Sub



Aaron Young
Analyst Programmer
ajyoung@pressenter.com
aarony@redwingsoftware.com