Bug? Memory leak with QVariantList containing allocated QObjects
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I am having a method returning a QVariantList containing allocated pointers. I tried the 'scoped pointers' however the compiler does not allow them to be converted to variants. Here is an example of the code:
[code]class CMyObject : public QObject
{
Q_OBJECT
protected:
QString m_sTitle;
QString m_sDescription;
};QVariant
CMyObjectManager::list()
{
QVariantList oList;
oList.append(QVariant::fromValue(new CMyObject));
oList.append(QVariant::fromValue(new CMyObject));
return QVariant::fromValue(oList);
}
[/code]The list is accessible in JavaScript within the browser, however the destructor of CMyObject is never called. The challenge is I have to dynamically generate the list, because the list is like a 'query' and each time a different list is returned.
I would like to know how can I return a list of objects and have Qt WebKit delete the objects when the variable goes out of scope.
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Hi,
I understand you have a memory leak. I my opinion, and according to the documentation, the arg of Q:Variant::fromValue is cont T &.
it means, You give it an object (a pointer in reality) and QVariant is going to duplicate it.Try something like this :
@CMyObject cMyObject;
oList.append(QVariant::fromValue(cMyObject));
@Regards.
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Thank you for your reply. I tried your solution and it crashes. This is because the object allocated on the stack is destroyed, and therefore JavaScript refers to a dangling pointer.
The QVariant does not duplicate the object (it does not know how). I wrote a ticket to Digia for a QObjectShared with a reference counter, similar as IUnknown and IDispatch are implemented.
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Hi,
QObject can't be copied and being copyable is mandatory for custom types to be used in a QVariant. QVariant::fromValue returns a variant containing a copy of the object passed.
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No there's not, "here":http://qt-project.org/doc/qt-5/qobject.html#no-copy-constructor-or-assignment-operator is the explanation about the copy restriction. In the case of QObject you can only use a pointer so it's the pointer that is copied not the object
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This is what I understood. What I need is a mechanism, typically a reference counter, to know when the variable in JavaScript goes out of scope. If there was a QObjectShared with a built-in reference counter, then the [virtual] destructor ~QObjectShared would indicate the object is out of scope.
