Determine when a TextBox control is scrolled

Determine when a TextBox control is scrolled

When the user scrolls the contents of a TextBox control – either by clicking on the companion scrollbars or by typing new characters in the edit area – the TextBox control sends its parent form a WM_COMMAND message, and passes its own hWnd property in lParam and the value EN_HSCROLL or EN_VSCROLL in the high word of wParam.

Therefore, to determine when the contents of a TextBox control, you can subclass its parent form, using the following code (based on the MsgHook DLL component):

' REQUIRES THE MSGHOOK.DLL COMPONENT'' you can omit the following constant definitions, ' because they are contained in the MsgHook type libraryConst WM_COMMAND = &H111Const EN_HSCROLL = &H601Const EN_VSCROLL = &H602Dim WithEvents FormHook As MsgHookPrivate Sub Form_Load()    ' start form subclassing     Set FormHook = New MsgHook    FormHook.StartSubclass hWndEnd SubPrivate Sub FormHook_AfterMessage(ByVal uMsg As Long, ByVal wParam As Long, _    ByVal lParam As Long, retValue As Long)    If uMsg = WM_COMMAND Then        ' The user selects a command item from a menu,        ' or a control sends a notification message to its parent window,        ' or an accelerator keystroke is translated.        '        ' If this is a notification from a control, lParam holds its handle.        If lParam = Text1.hWnd Then            ' In this case, the notification message is in the            ' high-order word of wParam.            ' NOTE: this msg doesn't arrive if the scroll bar indicator is             ' scrolled.            Select Case (wParam  &H10000)                Case EN_HSCROLL                    ' The TextBox control has been scrolled horizontally                Case EN_VSCROLL                    ' The TextBox control has been scrolled vertically            End Select        End If    End IfEnd Sub

Note that the WM_COMMAND message is sent only when the TextBox scrolls because new chars have been entered, or because the user clicked on the scrollbar’s arrow buttons. No messsage is sent when the scrollbar’s thumb indicator is moved.Finally, notice that you can use the same code to determine scrolling activity for all the TextBox controls on the form, simply by comparing the value in lParam with the handle of all the TextBox control you want to monitor.

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