Christopher Greaves

416-621-9348 cgreaves@chrisgreaves.com
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A Means Of Implementing “Undo” On GUI Forms ; Legalities ; The GUI Form ; The Data Control Events ; The Preservation Structure ; Initializing The Form ; Recording A Change ; Undoing A Change ; Inhibiting Undo ; Running The Form

Undoing A Change

In a general sense, this is merely the reverse of preserving a change:

Function GUI_Undo()
With typ(UBound(typ))
Me.cb1 = .blncb1
Me.cb2 = .blncb2
Me.ob1 = .blnob1
Me.ob2 = .blnob2
Me.ob3 = .blnob3
Me.tb1 = .strtb1
Me.tb2 = .strtb2
End With
ReDim Preserve typ(UBound(typ) - 1)
End Function

However we must consider several things:

We ought not to permit an “undo” operation if there are no changes to be undone

We want to inhibit preservation of changes when such changes are not a direct consequence of user action. Two examples are (a) initialization of the controls during the user form initialization and (b) re-initialization of user form controls during the edit-undo operation.

To this end we introduce a simple global Boolean switch to inhibit recording:

    Dim blnInhibit As Boolean
Function GUI_Preserve()
If blnInhibit Then
Else
ReDim Preserve typ(UBound(typ) + 1)
With typ(UBound(typ))
.blncb1 = Me.cb1
.blncb2 = Me.cb2
.blnob1 = Me.ob1
.blnob2 = Me.ob2
.blnob3 = Me.ob3
.strtb1 = Me.tb1
.strtb2 = Me.tb2
End With
End If
End Function

We set and unset the switch around user form initialization, and we set and unset the switch around the undo operation.

Private Sub UserForm_Initialize()
blnInhibit = True
ReDim typ(0)
''' In here set default values for the user form controls
blnInhibit = False
End Sub

Private Sub cmdUndo_Click()
blnInhibit = True
Call GUI_Undo
blnInhibit = False
End Sub

Inhibiting Undo

Toronto and Mississauga, Sunday, December 05, 2010 3:12 PM