Tooltips for each ListBox Item in visual basic 6

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Sorry to say but this method is BUGGY. It sometimes translates to the wrong list index. Try this one:

Top of Module ...

Private Type POINTAPI
                    X As Long
                    Y As Long
End Type

Private Declare Function ClientToScreen Lib "user32" (ByVal hwnd As Long, lpPoint As POINTAPI) As Long
Private Declare Function LBItemFromPt Lib "COMCTL32.DLL" (ByVal hLB As Long, ByVal ptX As Long, ByVal ptY As Long, ByVal bAutoScroll As Long) As Long

Private Sub List1_MouseMove(Button As Integer, Shift As Integer, X As Single, Y As Single)
On Error Resume Next

List1.ToolTipText = L.List(ItemUnderMouse(List1.hwnd, X, Y))
End Sub

Private Function ItemUnderMouse(ByVal list_hWnd As Long, ByVal X As Single, ByVal Y As Single)

Dim pt As POINTAPI:          pt.X = X \ Screen.TwipsPerPixelX:            pt.Y = Y \ Screen.TwipsPerPixelY
ClientToScreen list_hWnd, pt
ItemUnderMouse = LBItemFromPt(list_hWnd, pt.X, pt.Y, False)

End Function

Yeah, there's a difference between ComboBox and ListBox

This is how to do it with a ListBox :

Option Explicit

Private Type POINTAPI
    X As Long
    Y As Long
End Type

Private Declare Function GetCursorPos Lib "user32" (lpPoint As POINTAPI) As Long
Private Declare Function ScreenToClient Lib "user32" (ByVal hWnd As Long, lpPoint As POINTAPI) As Long
Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Long) As Long

Private Const LB_ITEMFROMPOINT = &H1A9

Private Sub Form_Load()
    Dim iIndex As Integer
    
    For iIndex = 1 To 100
        List1.AddItem "List Item " & iIndex
    Next
End Sub

Private Sub List1_MouseMove(Button As Integer, Shift As Integer, X As Single, Y As Single)
    Dim tPOINT As POINTAPI
    Dim iIndex As Long

    'get the Mouse Cursor Position
    Call GetCursorPos(tPOINT)
    'Convert the Coords to be Relative to the Listbox
    Call ScreenToClient(List1.hWnd, tPOINT)
    'Find which Item the Mouse is Over
    iIndex = SendMessage(List1.hWnd, LB_ITEMFROMPOINT, 0&, ByVal ((tPOINT.X And &HFF) Or (&H10000 * (tPOINT.Y And &HFF))))
    If iIndex >= 0 Then
        'Extract the List Index
        iIndex = iIndex And &HFF
        'set the Lists ToolTipText
        List1.ToolTipText = List1.List(iIndex)
    End If
End Sub

Now, if I were to do the same (well almost the same ) with the combobox :

Option Explicit

Private Type POINTAPI
    X As Long
    Y As Long
End Type

Private Declare Function GetCursorPos Lib "user32" (lpPoint As POINTAPI) As Long
Private Declare Function ScreenToClient Lib "user32" (ByVal hWnd As Long, lpPoint As POINTAPI) As Long
Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Long) As Long

Private Const LB_ITEMFROMPOINT = &H1A9
Const CB_SHOWDROPDOWN = &H14F

'to open cb list automatically
Sub ComboBoxOpenList(cbo As ComboBox, Optional showIt As Boolean = True)
    SendMessage cbo.hWnd, CB_SHOWDROPDOWN, showIt, ByVal 0&
End Sub

Private Sub Combo1_DropDown() 'drop down event
    Dim tPOINT As POINTAPI
    Dim iIndex As Long

    'get the Mouse Cursor Position
    Call GetCursorPos(tPOINT)
    'Convert the Coords to be Relative to the Listbox
    Call ScreenToClient(Combo1.hWnd, tPOINT)
    'Find which Item the Mouse is Over
    iIndex = SendMessage(Combo1.hWnd, LB_ITEMFROMPOINT, 0&, ByVal ((tPOINT.X And &HFF) Or (&H10000 * (tPOINT.Y And &HFF))))
    If iIndex >= 0 Then
        'Extract the List Index
        iIndex = iIndex And &HFF
        'set the Lists ToolTipText
        Combo1.ToolTipText = Combo1.List(iIndex)
    End If

End Sub

Private Sub Form_Load()
    Dim iIndex As Integer
    'Fill the List with Dummy Values
    For iIndex = 1 To 100
        Combo1.AddItem "Item " & iIndex
    Next
    ComboBoxOpenList Combo1, True 'automatically open dropdown list of combo
End Sub

The problem here is that it will ONLY show the tooltips when the list isn't dropped anymore.