Transparent ComboLBox

Printable View

I'm using the following code in an attempt to make a the listbox of a combobox transparent, with no luck tho. Add a combo to a form and try it please. It seems to just 'crash' the list.

VB Code:

Option Explicit
 
Private Declare Function GetComboBoxInfo Lib "user32.dll" _
  (ByVal hwndCombo As Long, _
  ByRef pcbi As PCOMBOBOXINFO) As Long
  
Private Declare Function SetWindowLong Lib "user32.dll" Alias "SetWindowLongA" _
  (ByVal hwnd As Long, _
  ByVal nIndex As Long, _
  ByVal dwNewLong As Long) As Long
  
Private Declare Function GetWindowLong Lib "user32.dll" Alias "GetWindowLongA" _
  (ByVal hwnd As Long, _
  ByVal nIndex As Long) As Long
     
Private Declare Function SetLayeredWindowAttributes Lib "user32.dll" _
  (ByVal hwnd As Long, _
  ByVal crKey As Long, _
  ByVal bAlpha As Byte, _
  ByVal dwFlags As Long) As Long
     
Private Type RECT
  Left As Long
  Top As Long
  Right As Long
  Bottom As Long
End Type
 
Private Type PCOMBOBOXINFO
  cbSize As Long
  rcItem As RECT
  rcButton As RECT
  stateButton As Long
  hwndCombo As Long
  hwndItem As Long
  hwndList As Long
End Type
 
Private Const GWL_EXSTYLE As Long = -20
Private Const LWA_ALPHA As Long = &H2
Private Const WS_EX_LAYERED As Long = &H80000
 
Private Sub Form_Load()
  Combo1.AddItem "moo"
  Combo1.AddItem "meep"
  Combo1.AddItem "baaa"
 
  Dim pcbi As PCOMBOBOXINFO, lRet As Long
  
  pcbi.cbSize = Len(pcbi)
  
  lRet = GetComboBoxInfo(Combo1.hwnd, pcbi)
  
  Call SetWindowLong(pcbi.hwndList, GWL_EXSTYLE, GetWindowLong(pcbi.hwndList, GWL_EXSTYLE) Or WS_EX_LAYERED)
  Call SetLayeredWindowAttributes(pcbi.hwndList, 0, 50, LWA_ALPHA)
End Sub

Cheers, adehh.

Dec 19th, 2003, 05:37 PM
Madboy

1 Attachment(s)

I get this error dude.....

http://www.vbforums.com/attachment.php?postid=1585465
Dec 19th, 2003, 05:38 PM
adzzzz

It's win2k/xp only :p
-adehh
Dec 19th, 2003, 05:39 PM
Madboy

oh well:(
Dec 19th, 2003, 05:52 PM
Maldrid

Well I tried it and it just seems to drop the list down and then once I select something the list is still shown. It seems as if the refresh event for the form does not repaint the form or atleast that section of where the list is shown.
Dec 19th, 2003, 07:37 PM
adzzzz

Indeed, exactly the same result I get. It's the WS_EX_LAYERED flag that causes it, maybe it's something that just cannot be done..

-adehh
Dec 20th, 2003, 01:15 AM
adzzzz

I've sussed it - why it won't work that is. The ComboLBoxes containing the list for the ComboBox work by being a child of the desktop, thus making them the active window whilst still leaving focus to the current window. I discovered all of this from an article here.

This sort of child window (possibly only child windows of the desktop) don't seem to like having their layered window attributes set, they accept the WS_EX_LAYERED style and dissapear like all other windows but after trying to set LWA_ALPHA they crash and all sorts of (what I believe are) repainting errors occur.

Bummer of Windows I suppose - cheers, adehh.