为什么不可能为QPropertyAnimation开发qobject_cast

Question

下面是QPropertyAnimation的创建代码：

    void CustomGraphicsScene::addAnimation(AnimatedPixmapItem* item)
    {
        auto propertyAnimation = new QPropertyAnimation { item, "SpriteFrame" };
        connect(propertyAnimation, &QPropertyAnimation::destroyed, this, &CustomGraphicsScene::deleteAnimation);
        propertyAnimation->setDuration(1000);
        propertyAnimation->setStartValue(0);
        propertyAnimation->setEndValue(10);
        propertyAnimation->start(QAbstractAnimation::DeleteWhenStopped);
}

这是我尝试使用QPropertyAnimation的位置：

    void CustomGraphicsScene::deleteAnimation()
    {
        auto propertyAnimation = qobject_cast<QPropertyAnimation*>(sender());
        if (propertyAnimation) { // Always false
            // Some code
        }
    }

Answer 1

qobject_cast不仅执行强制转换，还使用QMetaObject验证QObject是否仍然有效，例如，如果在构建对象时打印propertyAnimation->metaObject()->className();，它将返回QPropertyAnimation，但在与已销毁的sender()->metaObject()->className()相关联的插槽中，它将返回QObject。

我的建议是使用finished，更改删除策略并在插槽中删除它。

void CustomGraphicsScene::addAnimation(AnimatedPixmapItem* item)
{
        auto propertyAnimation = new QPropertyAnimation { item, "SpriteFrame" };
        connect(propertyAnimation, &QPropertyAnimation::finished, this, &CustomGraphicsScene::finishAnimation);
        propertyAnimation->setDuration(1000);
        propertyAnimation->setStartValue(0);
        propertyAnimation->setEndValue(10);
        propertyAnimation->start(QAbstractAnimation::KeepWhenStopped);
}

void CustomGraphicsScene::finishAnimation()
{
    auto propertyAnimation = qobject_cast<QPropertyAnimation*>(sender());
    if (propertyAnimation) { // Always false
        // Some code
        propertyAnimation->deleteLater();
    }
}