[英]QVariant to QObject*
I'm trying to attach a pointer to an QListWidgetItem
, to be used in the slot itemActivated
. 我正在尝试附加一个指向
QListWidgetItem
的指针,用于插槽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 itemActivated
slot. 现在我的问题,
itemActivated
插槽。 Here I need to extract my Image*
from the variant, and I don't know how to. 在这里,我需要从变体中提取我的
Image*
,我不知道如何。
I tried this, but I get the error: 我试过这个,但是我得到了错误:
'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 *>();
The answer is this 答案是这样的
// From QVariant to QObject *
QObject * obj = qvariant_cast<QObject *>(item->data(Qt::UserRole));
// from QObject* to myClass*
myClass * lmyClass = qobject_cast<myClass *>(obj);
That looks like an unusual use of QVariant
. 这看起来像
QVariant
一个不寻常的用途。 I'm not even sure if QVariant
would support holding a QObject
or QObject*
that way. 我甚至不确定
QVariant
是否支持以这种方式持有QObject
或QObject*
。 Instead, I would try deriving from QListWidgetItem
in order to add custom data, something like this: 相反,我会尝试从
QListWidgetItem
派生以添加自定义数据,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 Image
gets cleaned up. 此外,这个新类的析构函数为您提供了合理的逻辑,以确保您的
Image
得到清理。
You've inserted your Image class as QObject *, so get it out as QObject * also. 您已将Image类作为QObject *插入,因此也将其作为QObject *输出。 Then perform qobject_cast and everything should be fine
然后执行qobject_cast,一切都应该没问题
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