How to create n Objects dynamically to populate StackView
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@sandro4912 I ran your program. I removed the property index from QuizPage and got rid of "required" from question. It then showed the quiz correctly. When I clicked next question it crashed. Not sure what was wrong there.
@fcarney
you are right it does not work anymore. I will check that issue tomorrow and then come back to here. -
Of course I could change
required property var questionto
property var questionbut I thought it would be good to make it required to indicate the page only works with a question supplied. To me that all sounds like a weired bug that index is only available when you don't make a property required.
so
required property var indexlooks like a workarround.
@sandro4912 said in How to create n Objects dynamically to populate StackView:
To me that all sounds like a weired bug that index is only available when you don't make a property required.
That issue on SO was because the OP was not using "delegate" inside of Repeater. The relevance to "required" was due to the repeater not being able to set the property.
C++ is a perfectly valid school of magic.
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@sandro4912 said in How to create n Objects dynamically to populate StackView:
To me that all sounds like a weired bug that index is only available when you don't make a property required.
That issue on SO was because the OP was not using "delegate" inside of Repeater. The relevance to "required" was due to the repeater not being able to set the property.
@fcarney said in How to create n Objects dynamically to populate StackView:
That issue on SO was because the OP was not using "delegate" inside of Repeater. The relevance to "required" was due to the repeater not being able to set the property.
No, it was not because of not using
delegate, as a comment saiddelegateis a default property so you can omit it.
Repeater { Item {} }is the same asRepeater { delegate : Item {} }.The problem was indeed because of the required property. Since Qt 5.15, if a delegate has a required property, the view won't assign the delegate context properties based on the roles of the model. It will only assign roles corresponding to the required properties present in the delegate.
https://doc.qt.io/qt-5/qtquick-modelviewsdata-modelview.html#models
To get finer control over which roles are accessible, and to make delegates more self-contained and usable outside of views, required properties can be used. If a delegate contains required properties, the named roles are not provided. Instead, the QML engine will check if the name of a required property matches that of a model role. If so, that property will be bound to the corresponding value from the model.
[...]
Note: model, index, and modelData roles are not accessible if the delegate contains required properties, unless it has also required properties with matching names.That's why you can't access
indexormodelDataif you don't declare them as required property inQuizPage.And instead of
index, you should usemodelData:delegate: QuizPage{ required property var modelData question: modelData }Note that
QQmlListPropertyis not meant to expose C++ data to QML, it is meant to allow the QML to populate a C++ list from QML.
You should useQList<QObject*>,QVariantListor even betterQAbstractListModelif you need a dynamic model.QQmlListPropertydoes work, but it's not its job. -
@fcarney said in How to create n Objects dynamically to populate StackView:
That issue on SO was because the OP was not using "delegate" inside of Repeater. The relevance to "required" was due to the repeater not being able to set the property.
No, it was not because of not using
delegate, as a comment saiddelegateis a default property so you can omit it.
Repeater { Item {} }is the same asRepeater { delegate : Item {} }.The problem was indeed because of the required property. Since Qt 5.15, if a delegate has a required property, the view won't assign the delegate context properties based on the roles of the model. It will only assign roles corresponding to the required properties present in the delegate.
https://doc.qt.io/qt-5/qtquick-modelviewsdata-modelview.html#models
To get finer control over which roles are accessible, and to make delegates more self-contained and usable outside of views, required properties can be used. If a delegate contains required properties, the named roles are not provided. Instead, the QML engine will check if the name of a required property matches that of a model role. If so, that property will be bound to the corresponding value from the model.
[...]
Note: model, index, and modelData roles are not accessible if the delegate contains required properties, unless it has also required properties with matching names.That's why you can't access
indexormodelDataif you don't declare them as required property inQuizPage.And instead of
index, you should usemodelData:delegate: QuizPage{ required property var modelData question: modelData }Note that
QQmlListPropertyis not meant to expose C++ data to QML, it is meant to allow the QML to populate a C++ list from QML.
You should useQList<QObject*>,QVariantListor even betterQAbstractListModelif you need a dynamic model.QQmlListPropertydoes work, but it's not its job.Thanks for clarify. I was very confused how to expose my randomQuestions correctly.
Now comes the big Question.
Currently it is like this:
All Questions are in a class Derived from
QSqlTableModel.Now for RandomQuestions currently I create with an additional function in that class the
QQmlListProperty<Questions>.Wouldn't it the best to implement
QSortFilterProxModelwhich picks um the required random questions to expose that to QML?
