C++ QVariant 到 QObject*
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QVariant to QObject*
提问by Leonardo M. Ramé
I'm trying to attach a pointer to an QListWidgetItem, to be used in the slot itemActivated.
我正在尝试将指针附加到QListWidgetItem，以在 slot 中使用itemActivated。
The pointer I'm trying to attach is a QObject*descendant, so, my code is something like this:
我试图附加的指针是一个QObject*后代，所以，我的代码是这样的：
Image * im = new Image();
// here I add data to my Image object
// now I create my item
QListWidgetItem * lst1 = new QListWidgetItem(*icon, serie->getSeriesInstanceUID(), m_iconView);
// then I set my instance to a QVariant
QVariant v(QMetaType::QObjectStar, &im)
// now I "attach" the variant to the item.
lst1->setData(Qt::UserRole, v);
//After this, I connect the SIGNAL and SLOT
...
Now my problem, the itemActivatedslot. Here I need to extract my Image*from the variant, and I don't know how to.
现在我的问题，itemActivated插槽。在这里，我需要Image*从变体中提取我的，但我不知道该怎么做。
I tried this, but I get the error:
我试过这个，但我收到错误：
‘qt_metatype_id' is not a member of ‘QMetaTypeId'
“qt_metatype_id”不是“QMetaTypeId”的成员
void MainWindow::itemActivated( QListWidgetItem * item )
{
Image * im = item->data(Qt::UserRole).value<Image *>();
qDebug( im->getImage().toAscii() );
}
Any hint?
任何提示？
Image * im = item->data(Qt::UserRole).value<Image *>();
回答by Leonardo M. Ramé
The answer is this
答案是这个
// From QVariant to QObject *
QObject * obj = qvariant_cast<QObject *>(item->data(Qt::UserRole));
// from QObject* to myClass*
myClass * lmyClass = qobject_cast<myClass *>(obj);
回答by aschepler
That looks like an unusual use of QVariant. I'm not even sure if QVariantwould support holding a QObjector QObject*that way. Instead, I would try deriving from QListWidgetItemin order to add custom data, something like this:
这看起来像QVariant. 我什至不确定是否QVariant会支持持有QObject或QObject*那样。相反，我会尝试派生QListWidgetItem以添加自定义数据，如下所示：
class ImageListItem : public QListWidgetItem
{
// (Not a Q_OBJECT)
public:
ImageListItem(const QIcon & icon, const QString & text,
Image * image,
QListWidget * parent = 0, int type = Type);
virtual ~ImageListItem();
virtual QListWidgetItem* clone(); // virtual copy constructor
Image * getImage() const;
private:
Image * _image;
};
void MainWindow::itemActivated( QListWidgetItem * item )
{
ImageListItem *image_item = dynamic_cast<ImageListItem*>(item);
if ( !image_item )
{
qDebug("Not an image item");
}
else
{
Image * im = image_item->getImage();
qDebug( im->getImage().toAscii() );
}
}
Plus, the destructor of this new class gives you somewhere logical to make sure your Imagegets cleaned up.
另外，这个新类的析构函数为您提供了一个合乎逻辑的地方，以确保您Image得到清理。
回答by Kamil Klimek
You've inserted your Image class as QObject *, so get it out as QObject * also. Then perform qobject_cast and everything should be fine
您已将 Image 类作为 QObject * 插入，因此也将其作为 QObject * 取出。然后执行 qobject_cast 一切都应该没问题
