[Interest] QGaphicsItem deletion

[Igor Mironchik]

Hello.

On 15.06.2016 16:59, Konstantin Shegunov wrote:
> Hello,
>
>
> On Wed, Jun 15, 2016 at 4:15 PM, Igor Mironchik 
> <igor.mironchik at gmail.com <mailto:igor.mironchik at gmail.com>> wrote:
>
>     Parent of the handles is the same as Line's. But Line own objects
>     of handles with QScopedPointer.
>
>
> This doesn't sound right. If the handles are not children to the line, 
> then the line doesn't own them. Leaving semantics aside, it sounds 
> you're trying to "hijack" the ownership from the parent by using these 
> scoped pointers.

Exactly. I need to Line be as parent of handles but they should be 
parented to the scene (read form in my app) because I need 
boundingRect() to return exactly bounding rectangle of the line without 
handles. An I need handles to be removed with the Line if Line deleted.

I know that I can implement my own method in Line like 
boundingRectOfLine() and make handles children of Line. May be it would 
be a better solution, but at this time I have such code and it work...

>     So my question is it possible that handle will be deleted before
>     Line, so QScopedPointer will try to free already deleted pointer?
>
>
> From your description I'd guess this is exactly what's happening.

Here you aren't right. In d_tor() of QGraphicsScene I see:

while (!d->topLevelItems.isEmpty())
         delete d->topLevelItems.first();

where topLevelItems are in creating order...

and in QGraphicsItem d_tor()

while (!d_ptr->children.isEmpty())
             delete d_ptr->children.first();

So when Line deleted it places before handles in children list, and 
before Line deleted handles already deleted and removed from children list.

>
> Kind regards.
>
>
> On Wed, Jun 15, 2016 at 4:15 PM, Igor Mironchik 
> <igor.mironchik at gmail.com <mailto:igor.mironchik at gmail.com>> wrote:
>
>     Hi folks,
>
>     Let's say I have QGraphicsItem, let it be Line. This Line has move
>     handles - another QGraphicsItems, rectangles. Parent of the
>     handles is the same as Line's. But Line own objects of handles
>     with QScopedPointer.
>
>     When Line creates in c_tor() it creates handles, so handles adds
>     to the scene after Line. When I delete Line from the scene by hand
>     everything is fine: Line deletes and QScopedPointers free handles.
>
>     But if I close application and scene destroys with d_tor() in
>     which it deletes all child items. So my question is it possible
>     that handle will be deleted before Line, so QScopedPointer will
>     try to free already deleted pointer?
>
>     Thank you.
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