[Qt-interest] deleteLater() for QGraphicsItem

[Andreas Unger]

On Thu, Dec 3, 2009 at 4:19 AM, Daniel Price <daniel.price at fxhome.com>wrote:

>  We hit the same problem but there is a really simply solution – when you
> remove the item from the scene, wrap the pointer to in a QObject-derived
> class which calls deleteLater() in the constructor. Create this object on
> the heap with new() but ignore the return pointer. In the destructor, delete
> the graphics item. Here’s my templated version that can be used with any
> type:
>
>
>
> #include <QObject>
>
>
>
> template <typename T>
>
> class DelayedDelete : public QObject
>
> {
>
> public:
>
>                 explicit DelayedDelete(T *&item) : m_item(item)
>
>                 {
>
>                                 item = 0;
>
>                                 deleteLater();
>
>                 }
>
>                 virtual ~DelayedDelete()
>
>                 {
>
>                                 delete m_item;
>
>                 }
>
> private:
>
>                 T *m_item;
>
> };
>
>
>
> You’ll notice that the constructor takes a reference to the original
> pointer which it sets to 0 after copying it in the initialize list – this
> avoid leaving a hanging pointer in the calling code which DelayedDelete has
> taken ownership of. Here’s how it’s called:
>
>
>
> scene->removeItem(gfxItem);
>
> new DelayedDelete<RectItem>(gfxItem); // would have crashed if gfxItem was
> deleted here
>
>
>
> Where RectItem is my QGraphicsItem-derived class. As you can see it’s
> fire-and-forget. Qt will delete the DelayedDelete instance during the next
> event loop. But as far as your code is concerned, gfxItem is dead.
>

Fantastic! This worked for me.

Thanks a lot,
Andreas
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