Access Violation exception in PowerPoint after "undo"
I am experiencing an access violation exeption in PowerPoint if an "undo" call deletes a previously inserted shape that is currently selected
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Phil Paul
Guest
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Dear Add-In express Team,
I am experiencing a system.access.violation exception in the following Scenario and would really appreciate any hint after breaking my head on this and looking through all sort of posts for two days
The error can be reduced by a very simple example (as shown below):
I have the WindowSelectionChange event check work with the selected shapes. I check the selection type and if this is >=2 I access the selection.shaperange. This generally works fine.
But when I insert a shape via code and the user executes "undo" while the inserted shape is selected the program throws an access.vioalation exception. The reason is that the selection.type property is still on "2" (shapeRange selected) eventhough the "undo" deletes the selected shape so that actually nothing is selected after the undo call.
The really strange thing is that this ONLY happens if the inserted shape is a group, all other
shapeTypes (simple autoshapes, Charts, smart arts, Pictures etc.) can be deleted by the undo call and the correct selection type (0) is restored.
This simple example reproduces the issue
'// Started via keyboard shortcut
Sub copyAndInsertAGroupShape() Handles AdxKeyboardShortcut1.Action
'// Declare variables
Dim w As DocumentWindow = PowerPointApp.ActiveWindow
Dim sel As Selection = w.Selection
Dim slRange As SlideRange = sel.SlideRange
Dim sl As Slide = slRange.Item(1)
Dim ss As Shapes = sl.Shapes
'// The first shape on the slide must be a group for the error to show
Dim s As Shape = ss.Item(1)
'// Copy the shape and paste it on
Dim tmpRange As ShapeRange = s.Duplicate
Dim newShape As Shape = tmpRange.Item(1)
'// I select the shape here but error also shows if shape is selected manually
newShape.Select()
'// Releasing ComObjects or not makes no difference for the error
ReleaseComObject(newShape)
ReleaseComObject(tmpRange)
ReleaseComObject(ss)
ReleaseComObject(sl)
ReleaseComObject(slRange)
ReleaseComObject(s)
ReleaseComObject(sel)
ReleaseComObject(w)
'// resetting for test purposes so we can try multiple times
eventCompleted = True
End Sub
Private eventCompleted As Boolean = False
'// SelectionChange Event needs to check the selection type correctly
Private Sub WindowSelectionChange(sender As Object, hostObj As Object) Handles AdxPowerPointAppEvents1.WindowSelectionChange
'// just so you do not get into an infinite loop
If Not eventCompleted Then Exit Sub
eventCompleted = False
Dim myWindow As DocumentWindow = Nothing
Dim mySelection As Selection = Nothing
myWindow = PowerPointApp.ActiveWindow
mySelection = myWindow.Selection
'// The problem starts here: clicking "undo" in PowerPoint deletes the shape,
'// but the selection type still shows selection type = 2
If mySelection.Type >= 2 Then
Dim myShapeRange As ShapeRange = Nothing
'// This line fails with an access.violation exception
'// but ONLY if the shape is a group
myShapeRange = mySelection.ShapeRange
ReleaseComObject(myShapeRange)
End If
ReleaseComObject(mySelection)
ReleaseComObject(myWindow)
'// Event went well execute next time as well
eventCompleted = True
End Sub
What I have tried
> I tried different code combinations with and without releasing the com objects, also Setting them to nothing and forcing garbage Collection: no effect
> I checked the selection type also with pure VBA - also there the selection type after the undo is wrong
> I tried handling the access violation. This generally prevents the error from showing directly but after clicking around a little bit, PowerPoint will crash.
> I tried "selection.unselect" to execute after the undo call. This will also prevent the error from showing but creates a very bad user experience with the user selection being deselected by the add-in.
My question
> What is the best approach to deal with this issue?
One possibility would be to somehow check if selection.shaperange has a "bad pointer". Is this possible without actually throwing the access violation exception?
Best regards and thank you very much for any hint,
Phil |
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Posted 03 Apr, 2017 14:44:36
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Andrei Smolin
Add-in Express team
Posts: 18819
Joined: 2006-05-11
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Hello Phil,
Nice job!
A minor thing that doesn't influence anything is: the hostObj parameter of the WindowSelectionChange event already contains a PowerPoint.Selection object.
I confirm the issue. It occurs in PowerPoint 2016. It doesn't occur in PowerPoint 2010 and 2013.
If you duplicate a shape using the code above, then, after you click Undo, no sizing handles aren't shown for the shape, PowerPoint 2010-2016 hides the Drawing Tools | Format tab, and the Selection object for the active window reports Selection.Type=ppSelectionNone. This is expected.
If you duplicate a group using the code above, then, after you click Undo, sizing handles aren't shown for the shape thus indicating that the shape isn't selected. Still, PowerPoint 2010-2013 continues to display the Drawing Tools | Format tab, while the PowerPoint.Selection object for the active window reports Selection.Type=ppSelectionShapes. Getting Selection.ShapeRange in this situation produces different results: in PowerPoint 2010-2013, the call succeeds, in PowerPoint 2016 it causes an AcessViolationException.
I'm going to create a VSTO add-in demonstrating the issue and post it on the Office development forum at https://social.msdn.microsoft.com/Forums/en-US/home?forum=officegeneral. I'll publish a link here when I do this.
Phil Paul writes:
> I tried "selection.unselect" to execute after the undo call. This will also prevent the error from showing but creates a very bad user experience with the user selection being deselected by the add-in.
I believe this may be a correct workaround. You need to check if you undo a duplicated group before deslecting.
Andrei Smolin
Add-in Express Team Leader |
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Posted 04 Apr, 2017 04:48:14
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Andrei Smolin
Add-in Express team
Posts: 18819
Joined: 2006-05-11
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Posted 04 Apr, 2017 07:13:03
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Phil Paul
Guest
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Dear Andrei,
first of all thank you for looking into the topic. Thank you for posting the link.
I will be interested to see if a solution is found!
To me it is at least good news that the error is not popping up in PowerPoint 2010 and 2013.
I will create a workaround for PowerPoint 2016.
Do you know if it is possible to check if the selection.shaperange is corrupted? Something in the line of
if hasBadPointer(selection.shaperange) then ...
I am not aware if there is a way to check the state of the selection.shaperange without actually throwing the access.violation excection.
best regards,
Phil |
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Posted 04 Apr, 2017 07:48:38
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Andrei Smolin
Add-in Express team
Posts: 18819
Joined: 2006-05-11
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Hello Phil,
I doubt that a solution will be found; the issue looks like a bug in PowerPoint 2016. If so, we will need to wait for them to fix it.
Phil Paul writes:
Do you know if it is possible to check if the selection.shaperange is corrupted?
The only way is to call Selection.ShapeRange and get that exception.
Andrei Smolin
Add-in Express Team Leader |
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Posted 04 Apr, 2017 08:47:27
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Phil Paul
Guest
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Thank you very much Andrei for your response.
I'll go for a (bit more complex) workaround then. |
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Posted 04 Apr, 2017 09:04:23
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Andrei Smolin
Add-in Express team
Posts: 18819
Joined: 2006-05-11
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You are welcome!
Andrei Smolin
Add-in Express Team Leader |
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Posted 04 Apr, 2017 10:13:30
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Andrei Smolin
Add-in Express team
Posts: 18819
Joined: 2006-05-11
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Posted 07 Apr, 2017 03:31:35
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Phil Paul
Guest
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Hi Andrei,
thank you for this: I cast my vote... hope it gets picked up.
Phil |
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Posted 08 Apr, 2017 00:15:30
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