dcsimg
Login | Register   
RSS Feed
Download our iPhone app
TODAY'S HEADLINES  |   ARTICLE ARCHIVE  |   FORUMS  |   TIP BANK
Browse DevX
Sign up for e-mail newsletters from DevX

By submitting your information, you agree that devx.com may send you DevX offers via email, phone and text message, as well as email offers about other products and services that DevX believes may be of interest to you. DevX will process your information in accordance with the Quinstreet Privacy Policy.


Tip of the Day
Language: VB4/32,VB5,VB6
Expertise: beginner
Jan 29, 2000

WEBINAR:

On-Demand

Application Security Testing: An Integral Part of DevOps


Undo changes in a TextBox control

The TextBox control supports the capability to undo changes, but there is no property or method that exposes this feature. You can achieve the same goal with a a set of messages.


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 EM_CANUNDO = &HC6
Const EM_UNDO = &HC7
Const EM_EMPTYUNDOBUFFER = &HCD

The EM_CANUNDO message returns a non-zero value if the contents of the TextBox control can undone. The EM_UNDO message actually undoes all changes:. The following code demonstrates how you can use these messages in a typical Edit menu:


Private Sub mnuEdit_Click()
    If TypeOf ActiveControl Is TextBox Then
        ' check whether changes to the current 
        ' TextBox control can be undone
        mnuEditUndo.Enabled = SendMessage(ActiveControl.hWnd, EM_CANUNDO, 0, _
            ByVal 0&)
    Else
        ' in all other cases, disable this menu command
        mnuEditUndo.Enabled = False
    End If
End Sub

Private Sub mnuEditUndo_Click()
    ' Undo the most recent edit operation on the active control 
    ' (no need to use TypeOf...Is to check the control's type)
    SendMessage ActiveControl.hWnd, EM_UNDO, 0, ByVal 0&
End Sub

Finally, the EM_EMPTYUNDOBUFFER clears the internal undo buffer, so that the user can't undo changes.

SendMessage ActiveControl.hWnd, EM_EMPTYUNDOBUFFER, 0, ByVal 0&
Francesco Balena
 
Comment and Contribute

 

 

 

 

 


(Maximum characters: 1200). You have 1200 characters left.

 

 

Sitemap
Thanks for your registration, follow us on our social networks to keep up-to-date