Microsoft KB Archive/153633

= How to Determine If Text in a Text Box Can Be Undone =

Article ID: 153633

Article Last Modified on 6/28/2004

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APPLIES TO


 * Microsoft Visual Basic 4.0 Standard Edition
 * Microsoft Visual Basic 4.0 Professional Edition
 * Microsoft Visual Basic 4.0 Professional Edition
 * Microsoft Visual Basic 4.0 16-bit Enterprise Edition
 * Microsoft Visual Basic 4.0 32-Bit Enterprise Edition

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This article was previously published under Q153633



SUMMARY
This article shows by example how you can determine at any given point if the text entered into a text box can be undone.



MORE INFORMATION
You can send an EM_CANUNDO message to a TextBox control to determine whether an operation on it can be undone; that is, whether the control can respond to the EM_UNDO message. If the TextBox control can correctly process the EM_UNDO message, the return value from SendMessage is TRUE; otherwise, it is FALSE.

Step-by-Step Example
 Start a new project in Visual Basic 4.0. Form1 is added by default. Add a text box (Text1) to Form1.  Add the following code to the General Declaration portion of Form1: Const EM_CANUNDO = &HC6 Private Declare Function SendMessage Lib "user32" Alias _ "SendMessageA" _     (ByVal hwnd As Long, ByVal wMsg As Long,   ByVal wParam As Long, ByVal _    lParam As Long) As Long

Private Sub Form_Click Dim lRet As Long

lRet = SendMessage(Text1.hwnd, EM_CANUNDO, 0&, 0&) Debug.Print lRet End Sub  Press F5 to run the program. Type some text into the text box and click Form1. The Debug window will display a value of 1 indicating that the text just entered can be undone. Note that if no text is typed into the text box and the form is clicked, SendMessage will return 0, as there is nothing to undo.

Additional query words: 4.00 vb4win vb4all

Keywords: KB153633

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