[Qt-interest] Best way to implement "onShow/onHide" animation when GraphicsItem gets added/removed from scene?

[Anders Bakken]

On Thu, Jul 22, 2010 at 11:47:39PM +0100, Carl Snellman wrote:
> Hey,
>
> I'm trying to implement an animation to a QGraphicsItem derivate, and
> I'd like the animation to scale the item from 0 to 1 when the item is
> added, and then when removed from scene, it would shrink away (scale
> 1->0). I got the "onShow" animation working fine, but "onHide" (or
> onRemoval) causes me headaches. I tried the following:
> >>>>>>>>>>>>>>>>>>>>>>>>
> QVariant MyObject::itemChange(GraphicsItemChange change, const
> QVariant &value) {
>      if (change == QGraphicsItem::ItemVisibleChange && scene()) {
>          bool visible = value.toBool();
>          QPropertyAnimation * sizeAnimation = new
> QPropertyAnimation(this, "scale");
>          sizeAnimation->setDuration(700);
>          sizeAnimation->setEasingCurve(QEasingCurve::OutBounce);
>          if(visible) {
>              qDebug() << "MyObject::itemChange onShow";
>              setScale(0);
>              sizeAnimation->setEndValue(1); // grow to normal size
>          } else {
>             qDebug() << "MyObject::itemChange onHide";
>             sizeAnimation->setEndValue(0); // shrink away
>          }
>          sizeAnimation->setLoopCount(1);
>          sizeAnimation->start();
>      }
>      return QGraphicsItem::itemChange(change, value);
>  }
> <<<<<<<<<<<<<<<<<<<<<<<<
> As said, onShow anim is okay, but the ItemVisibleChange for hide never
> happens if the object is removed from scene. So I tried the following:
> >>>>>>>>>>>>>>>>>>>>>>>>>>>>
> QVariant MyObject::itemChange(GraphicsItemChange change, const
> QVariant &value) {
>     if (change == QGraphicsItem::ItemSceneChange) {
>         QPropertyAnimation * sizeAnimation = new
> QPropertyAnimation(this, "scale");
>         sizeAnimation->setDuration(700);
>         sizeAnimation->setEasingCurve(QEasingCurve::OutBounce);
>         if( ! value.isNull()) {
>             qDebug() << "MyObject::itemChange onSceneAdd";
>             setScale(0);
>             sizeAnimation->setEndValue(1); // grow to normal size
>         } else {
>            qDebug() << "MyObject::itemChange onSceneRemove";
>            sizeAnimation->setEndValue(0); // shrink away
>         }
>         sizeAnimation->setLoopCount(1);
>         sizeAnimation->start();
>     }
>  }
> <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
> Again, onShow works fine, but when the item is removed from scene, it
> gets the event with value non-null !??!?!
> So looks like that won't work either as an approach.
>
> Would anyone have any ideas how to implement such functionality? There
> is also one more complication: I'd like to have the object
> self-destruct when the animation is finished... Otherwise I'd need to
> react on the anim finished() signal somewhere and delete the object
> then. Any ideas how to implement self-destruct?
>
> Carl

Why don't you just call your own function when removing items from the
scene? AFAIK QGraphics.* will never remove an item from a scene for you
(unless maybe if you're adding it to another scene).

regards

--
Anders Bakken

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