Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" ( _
    ByVal hwnd As Integer, ByVal wMsg As Integer, _
    ByVal wParam As Integer, ByVal lParam As Object) As Integer
 
    Private Const EM_GETLINECOUNT As Integer = &HBA
 
    Public Function GetLinesCount(ByVal txtCtl As TextBoxBase) As Integer
        Return SendMessage(txtCtl.Handle.ToInt32, EM_GETLINECOUNT, -1, Nothing)
    End Function