Limit the length of the text in a TreeView node

The TreeView control doesn’t expose any property that lets you limit the amount of text users can type when editing a Node’s label. However, you can do the trick with a couple of SendMessage API calls from within the BeforeLabelEdit event: with the TVM_GETEDITCONTROL message you retrieve the handle of the hidden Edit control that the TreeView creates for let the user edit the node. If you then send the EM_LIMITTEXT message to this Edit control you can put a limit to the text that can be typed in this control:

Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal _    hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, _    lParam As Any) As LongConst TV_FIRST = &H1100Const TVM_GETEDITCONTROL = TV_FIRST + 15Const EM_LIMITTEXT = &HC5' limit the text that can be typed in TreeView1's node to 20 charactersPrivate Sub TreeView1_BeforeLabelEdit(Cancel As Integer)    Dim editHWnd As Long    ' get the handle of the TreeView's Edit control    editHWnd = SendMessage(TreeView1.hWnd, TVM_GETEDITCONTROL, 0, ByVal 0&)    ' send it a EM_LIMITTEXT message to limit its length    SendMessage editHWnd, EM_LIMITTEXT, 20, 0End Sub

Once you now the method you can perform some other tricks with the Edit control. For example, you can automatically 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 LongPrivate Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" _    (ByVal hWnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As LongPrivate Declare Function GetWindowLong Lib "user32" Alias "GetWindowLongA" _    (ByVal hWnd As Long, ByVal nIndex As Long) As LongPrivate Const GWL_STYLE = (-16)Const TV_FIRST = &H1100Const TVM_GETEDITCONTROL = TV_FIRST + 15Const ES_UPPERCASE = &H8&' force the text typed in a TreeView's node to uppercasePrivate Sub TreeView1_BeforeLabelEdit(Cancel As Integer)    Dim editHWnd As Long        ' get the handle of the TreeView's Edit control    editHWnd = SendMessage(TreeView1.hWnd, TVM_GETEDITCONTROL, 0, ByVal 0&)    ' force the all-uppercase style    SetWindowLong editHWnd, GWL_STYLE, GetWindowLong(editHWnd, _        GWL_STYLE) Or ES_UPPERCASEEnd Sub

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