> Sounds to me, you are looking for a QStringListModel. I am not sure how qstringlistmodel will help matters tbh
> There is no simple solution for this. So, should I send the value from qml to c++ to do a search there instead? It's the solution I ended up doing but I hoped storing something on JS side was possible to not cross language boundaries on each item initialization. On Mon, Oct 23, 2023 at 4:35 PM Ulf Hermann via Interest < interest@qt-project.org> wrote: > Hi Nikolai, > > it would be interesting to see the QML code that produces this behavior. > However, I can very well imagine what's happening there. This is likely > the "value type reference" problem. The list is a "sequence type". It > doesn't have an identity of its own but rather is only accessible as a > copy from your property. However, in JavaScript there is no such thing > as a value (or sequence) type. There are only objects and each object > has a unique identity. Therefore, your list, upon access from > JavaScript, is wrapped into a special JavaScript object so that you can > interact with it. The special object gives you the illusion of a > separate entity by refreshing its copy of the list whenever you read > from it and by writing the copy back to the property whenever you change > it. The illusion breaks down when you retrieve the list a second time, > though. Lacking any actual identity information, the QML engine cannot > find other instances of the same list when accessing it again. Therefore > it has to create a new wrapper object every time. > > In contrast to that, for QObject-derived types we have actual identity > information. QObjectPrivate has a field for "declarative data" and there > we store a pointer to the JavaScript wrapper. > > There is no simple solution for this. We could probably add some > book-keeping to our QObject wrapper in order to figure out which > properties already have sequence (and value type) wrappers. This is more > complicated than it sounds because value types can have properties of > their own, value types can be stored in lists, and all of this recursively. > > If you get qmlcachegen to compile the code to C++ with Qt6, you won't > see the JavaScript wrappers for lists and value types anymore. The > generated C++ code can store the values on the C++ stack instead. But > there are restrictions: In the generated C++ code we can _not_ honor the > object-like nature of value type and sequence references. Anything that > would exploit it won't be compiled to C++. In particular, any function > call and any writing to a property invalidates all value type and > sequence instances currently on the stack. This is because their source > properties may have been changed by code triggered from the function > call or property write. > > best regards, > Ulf > _______________________________________________ > Interest mailing list > Interest@qt-project.org > https://lists.qt-project.org/listinfo/interest >
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