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Tip of the Day
Language: VB5,VB6
Expertise: Intermediate
Jul 1, 2000



Building the Right Environment to Support AI, Machine Learning and Deep Learning

Get full control on the text typed in a ListView's item

The ListView control exposes the AfterLabelEdit event to let the programmer validate the text entered in a ListItem, but there is no way to trap keys as they are typed by the user. This prevents you from discarding unwanted characters while the user types them.

You can work around this problem by subclassing the Edit control that the ListView control creates when entering the node edit mode. The following code uses the MSGHOOK.DLL library, that you can download from the FileBank on this site, to discard digits and convert all text to uppercase:


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
Const LVM_FIRST = &H1000

Dim WithEvents TVHook As MsgHook

' start subclassing of the Edit control used when in edit mode

Private Sub ListView1_BeforeLabelEdit(Cancel As Integer)
    Dim editHWnd As Long
    ' get the handle of the TreeView's Edit control
    editHWnd = SendMessage(ListView1.hWnd, LVM_GETEDITCONTROL, 0, ByVal 0&)
    ' subclass it
    LVHook.StartSubclass editHWnd
End Sub

' stop subclassing when exiting edit mode

Private Sub ListView1_AfterLabelEdit(Cancel As Integer, NewString As String)
End Sub

Private Sub Form_Load()
    Set LVHook = New MsgHook
End Sub

' discard digits as they are entered by the user
' and convert all text to uppercase

Private Sub LVHook_BeforeMessage(uMsg As Long, wParam As Long, lParam As Long, _
    retValue As Long, Cancel As Boolean)
    If uMsg = WM_CHAR Then
        ' wParam contains the character code
        If wParam >= 48 And wParam <= 57 Then
            ' discard digits
            Cancel = True
        ElseIf wParam >= Asc("a") And wParam <= Asc("z") Then
            ' convert to uppercase
            wParam = wParam - 32
        End If
    End If
End Sub

Francesco Balena
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