Unsolved How to create n Objects dynamically to populate StackView
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@sandro4912 said in How to create n Objects dynamically to populate StackView:
QQmlListProperty
It looks like it is repeating, but not creating modelData. Not sure if QQmlListProperty is 100% supported, but it should be creating an "index" variable you can use.
Repeater{ model: randomQuestions delegate: QuizPage{ question: randomQuestions[index] } }
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I tried that but it also insist that index is not existing:
qrc:/qml/quiz/QuizPage.qml:51: TypeError: Cannot read property 'id' of undefined qrc:/qml/quiz/QuizPage.qml:56: TypeError: Cannot read property 'askedQuestion' of undefined qrc:/qml/quiz/QuizPage.qml:63: TypeError: Cannot read property 'picture' of undefined qrc:/qml/quiz/Quiz.qml:0: ReferenceError: index is not defined qrc:/qml/quiz/QuizPage.qml:51: TypeError: Cannot read property 'id' of undefined qrc:/qml/quiz/QuizPage.qml:56: TypeError: Cannot read property 'askedQuestion' of undefined qrc:/qml/quiz/QuizPage.qml:63: TypeError: Cannot read property 'picture' of undefined qrc:/qml/quiz/Quiz.qml:0: ReferenceError: index is not defined qrc:/qml/quiz/QuizPage.qml:51: TypeError: Cannot read property 'id' of undefined qrc:/qml/quiz/QuizPage.qml:56: TypeError: Cannot read property 'askedQuestion' of undefined qrc:/qml/quiz/QuizPage.qml:63: TypeError: Cannot read property 'picture' of undefined qrc:/qml/quiz/Quiz.qml:0: ReferenceError: index is not defined qrc:/qml/quiz/QuizPage.qml:51: TypeError: Cannot read property 'id' of undefined qrc:/qml/quiz/QuizPage.qml:56: TypeError: Cannot read property 'askedQuestion' of undefined qrc:/qml/quiz/QuizPage.qml:63: TypeError: Cannot read property 'picture' of undefined qrc:/qml/quiz/Quiz.qml:0: ReferenceError: index is not defined qrc:/qml/quiz/QuizPage.qml:51: TypeError: Cannot read property 'id' of undefined qrc:/qml/quiz/QuizPage.qml:56: TypeError: Cannot read property 'askedQuestion' of undefined qrc:/qml/quiz/QuizPage.qml:63: TypeError: Cannot read property 'picture' of undefined qrc:/qml/quiz/Quiz.qml:0: ReferenceError: index is not defined qrc:/qml/quiz/QuizPage.qml:51: TypeError: Cannot read property 'id' of undefined qrc:/qml/quiz/QuizPage.qml:56: TypeError: Cannot read property 'askedQuestion' of undefined qrc:/qml/quiz/QuizPage.qml:63: TypeError: Cannot read property 'picture' of undefined qrc:/qml/quiz/Quiz.qml:0: ReferenceError: index is not defined qrc:/qml/quiz/QuizPage.qml:51: TypeError: Cannot read property 'id' of undefined qrc:/qml/quiz/QuizPage.qml:56: TypeError: Cannot read property 'askedQuestion' of undefined qrc:/qml/quiz/QuizPage.qml:63: TypeError: Cannot read property 'picture' of undefined qrc:/qml/quiz/Quiz.qml:0: ReferenceError: index is not defined qrc:/qml/quiz/QuizPage.qml:51: TypeError: Cannot read property 'id' of undefined qrc:/qml/quiz/QuizPage.qml:56: TypeError: Cannot read property 'askedQuestion' of undefined qrc:/qml/quiz/QuizPage.qml:63: TypeError: Cannot read property 'picture' of undefined qrc:/qml/quiz/Quiz.qml:30: ReferenceError: index is not defined qrc:/qml/quiz/QuizPage.qml:51: TypeError: Cannot read property 'id' of undefined qrc:/qml/quiz/QuizPage.qml:56: TypeError: Cannot read property 'askedQuestion' of undefined qrc:/qml/quiz/QuizPage.qml:63: TypeError: Cannot read property 'picture' of undefined qrc:/qml/quiz/Quiz.qml:30: ReferenceError: index is not defined qrc:/qml/quiz/QuizPage.qml:51: TypeError: Cannot read property 'id' of undefined qrc:/qml/quiz/QuizPage.qml:56: TypeError: Cannot read property 'askedQuestion' of undefined qrc:/qml/quiz/QuizPage.qml:63: TypeError: Cannot read property 'picture' of undefined qrc:/qml/quiz/Quiz.qml:30: ReferenceError: index is not defined
Some more background information of random Questions.
A Question is defined like this:
class Question : public QObject { Q_OBJECT Q_PROPERTY(int id READ getId CONSTANT) Q_PROPERTY(QString askedQuestion READ getAskedQuestion CONSTANT) Q_PROPERTY(QString answer1 READ getAnswer1 CONSTANT) Q_PROPERTY(QString answer2 READ getAnswer2 CONSTANT) Q_PROPERTY(QString answer3 READ getAnswer3 CONSTANT) Q_PROPERTY(QString answer4 READ getAnswer4 CONSTANT) Q_PROPERTY(int correctAnswer READ getCorrectAnswer CONSTANT) Q_PROPERTY(QString picture READ getPicture CONSTANT) public: enum class Correct{ Answer1 = 1, Answer2 = 2, Answer3 = 3, Answer4 = 4 }; Question() = default; Question(int id, QString askedQuestion, QString answer1, QString answer2, QString answer3, QString answer4, Correct correctAnswer, QString picture = QString{}); int getId() const; QString getAskedQuestion() const; QString getAnswer1() const; QString getAnswer2() const; QString getAnswer3() const; QString getAnswer4() const; int getCorrectAnswer() const; QString getPicture() const; private: int mId; QString mAskedQuestion; QString mAnswer1; QString mAnswer2; QString mAnswer3; QString mAnswer4; Correct mCorrectAnswer; QString mPicture; };
In annother class which has sql connection I read the randomQuestions:
class QuestionSqlTableModel : public QSqlTableModel { Q_OBJECT Q_PROPERTY(QQmlListProperty<Question> randomQuestions READ getRandomQuestions NOTIFY randomQuestionsChanged) public: explicit QuestionSqlTableModel(QObject *parent = nullptr, const QSqlDatabase &db = QSqlDatabase()); Q_INVOKABLE QVariant data(const QModelIndex &index, int role) const override; Q_INVOKABLE bool addNewEntry(const QString& askedQuestion, const QString& answer1, const QString& answer2, const QString& answer3, const QString& answer4, int correctAnswer, const QString& picturePath); Q_INVOKABLE void generateNewRandomQuestions(int count); QQmlListProperty <Question> getRandomQuestions(); signals: void randomQuestionsChanged(); private: void appendRandomQuestion(Question *question); int randomQuestionsCount() const; Question* randomQuestionAt(int index) const; void randomQuestionsClear(); static void appendRandomQuestion( QQmlListProperty<Question>* list, Question *question); static int randomQuestionsCount(QQmlListProperty<Question>* list); static Question* randomQuestionAt( QQmlListProperty<Question>* list, int index); static void randomQuestionsClear(QQmlListProperty<Question>* list); QVector<Question*> mRandomQuestions; };
They get registered like this:
qmlRegisterAnonymousType<Question>("sandro.custom.types",1); auto context = engine.rootContext(); context->setContextProperty("questionSqlTableModel", questionSqlTableModel);
I pass the random questions like this to the Quiz:
ToolButton { text: qsTr("New Quiz") icon.name: "address-book-new" onClicked: { questionSqlTableModel.generateNewRandomQuestions(10) loader.setSource("quiz/Quiz.qml", {"randomQuestions": questionSqlTableModel.randomQuestions}) } }
What I could already do is show a single page likes this:
import QtQuick 2.15 import QtQuick.Controls 2.15 Item { id: quiz required property var randomQuestions width: parent.width height: parent.height QuizPage{ id: quizPage anchors.fill: parent question: randomQuestions[0] } }
This works without problem so I really wonder why the delegate solution does not work.
For completion here is QuizPage:
import QtQuick 2.15 import QtQuick.Layouts 1.15 import QtQuick.Controls 2.15 Item{ id: root required property var question property var __shuffledAnswers property bool __correctAnswer: false signal answeredCorrectly() signal answeredWrong() width: parent.width height: parent.height anchors.fill: parent Rectangle { id: dialog width: parent.width height: parent.height Component.onCompleted: { checkButton.enabled = false; nextQuestionButton.enabled = false; root.__shuffledAnswers = makeAnswerArray(question.answer1, question.answer2, question.answer3, question.answer4); shuffleArray(root.__shuffledAnswers); answer1TextField.text = root.__shuffledAnswers[0]; answer2TextField.text = root.__shuffledAnswers[1]; answer3TextField.text = root.__shuffledAnswers[2]; answer4TextField.text = root.__shuffledAnswers[3]; } ButtonGroup { id: radioGroup } ColumnLayout{ anchors.fill: parent RowLayout{ Text{ text: qsTr("Question: " + question.id) } } RowLayout{ Text{ text: qsTr(question.askedQuestion) } } RowLayout{ Image{ id: image source: question.picture.length > 0 ? "data:image/png;base64," + question.picture: "" } } RowLayout{ RadioButton{ id: radioButtonAnswer1 ButtonGroup.group: radioGroup onCheckedChanged: { if(checked) { checkButton.enabled = true if(root.question.correctAnswer === 1) { __correctAnswer = true } else { __correctAnswer = false } } } } AnswerTextField{ Layout.fillWidth: true id: answer1TextField } } RowLayout{ RadioButton{ id: radioButtonAnswer2 ButtonGroup.group: radioGroup onCheckedChanged: { if(checked) { checkButton.enabled = true if(root.question.correctAnswer === 2) { __correctAnswer = true } else { __correctAnswer = false } } } } AnswerTextField{ Layout.fillWidth: true id: answer2TextField } } RowLayout{ RadioButton{ id: radioButtonAnswer3 ButtonGroup.group: radioGroup onCheckedChanged: { if(checked) { checkButton.enabled = true if(root.question.correctAnswer === 3) { __correctAnswer = true } else { __correctAnswer = false } } } } AnswerTextField{ Layout.fillWidth: true id: answer3TextField } } RowLayout{ RadioButton{ id: radioButtonAnswer4 ButtonGroup.group: radioGroup onCheckedChanged: { if(checked) { checkButton.enabled = true if(root.question.correctAnswer === 4) { __correctAnswer = true } else { __correctAnswer = false } } } } AnswerTextField{ Layout.fillWidth: true id: answer4TextField } } RowLayout{ Layout.alignment: Qt.AlignRight Button{ id: checkButton text: qsTr("Check Answer") onPressed: { markAnswers(root.question.correctAnswer); disableRadioButtons(); enabled = false nextQuestionButton.enabled = true } } Button{ id: nextQuestionButton text: qsTr("Next Question") onPressed: { if(root.__correctAnswer) { root.answeredCorrectly() } else { root.answeredWrong() } } } } } } function makeAnswerArray(answer1, answer2, answer3, answer4) { return [answer1, answer2, answer3, answer4]; } function shuffleArray(array) { for (var i = array.length - 1; i > 0; i--) { var j = Math.floor(Math.random() * (i + 1)); var temp = array[i]; array[i] = array[j]; array[j] = temp; } } readonly property string correctAnswerColor: "#99FFCC" readonly property string wrongAnswerColor: "#FF9999" function markAnswers(correctAnswer) { switch(correctAnswer) { case 1: markAnswersIfAnswer1IsCorrect(); break; case 2: markAnswersIfAnswer1IsCorrect(); break; case 3: markAnswersIfAnswer1IsCorrect(); break; case 4: markAnswersIfAnswer1IsCorrect(); break; default: console.assert(false, "Invalid Value for correctAnswer: " + correctAnswer) } } function markAnswersIfAnswer1IsCorrect() { answer1TextField.backgroundColor = correctAnswerColor answer2TextField.backgroundColor = wrongAnswerColor answer3TextField.backgroundColor = wrongAnswerColor answer4TextField.backgroundColor = wrongAnswerColor } function markAnswersIfAnswer2IsCorrect() { answer1TextField.backgroundColor = wrongAnswerColor answer2TextField.backgroundColor = correctAnswerColor answer3TextField.backgroundColor = wrongAnswerColor answer4TextField.backgroundColor = wrongAnswerColor } function markAnswersIfAnswer3IsCorrect() { answer1TextField.backgroundColor = wrongAnswerColor answer2TextField.backgroundColor = wrongAnswerColor answer3TextField.backgroundColor = correctAnswerColor answer4TextField.backgroundColor = wrongAnswerColor } function markAnswersIfAnswer4IsCorrect() { answer1TextField.backgroundColor = wrongAnswerColor answer2TextField.backgroundColor = wrongAnswerColor answer3TextField.backgroundColor = wrongAnswerColor answer4TextField.backgroundColor = correctAnswerColor } function disableRadioButtons() { radioButtonAnswer1.enabled = false radioButtonAnswer2.enabled = false radioButtonAnswer3.enabled = false radioButtonAnswer4.enabled = false } }
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I remembered I had this index issue before and asked it on stack overflow:
https://stackoverflow.com/questions/62484078/required-property-not-working-with-repeaterSo solution is in QuizPage add:
required property int index
Than index can be accessed. Weired but thats the way.
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What does your repeater code look like?
It cannot inject a property into an object. It has to be set inside the repeater statement. -
Repeater code is like you suggested:
SwipeView{ id: quizSwipeView interactive: false anchors.fill: parent Repeater{ model: randomQuestions delegate: QuizPage{ question: randomQuestions[index] } } }
Item{ id: root required property var question required property int index //.... }
If I drop the required in question i can skip defining the index it is very weired behaviour.
See also here: https://stackoverflow.com/questions/62484078/required-property-not-working-with-repeater
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@sandro4912 said in How to create n Objects dynamically to populate StackView:
Item{
id: rootrequired property var question required property int index
//....
}What is the reason for this property index inside your object? This doesn't make sense if you are using "question" as your property.
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@sandro4912 said in How to create n Objects dynamically to populate StackView:
Repeater{
model: randomQuestions
delegate: QuizPage{
question: randomQuestions[index]
}
}What does this do?
Repeater{ model: randomQuestions delegate: Item{ Component.onCompleted: { console.log(index) } } }
This "should" print out the index for each entry in randomQuestions. If it doesn't then you need a data model Repeater can use.
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this
Repeater{ model: randomQuestions delegate: Item{ Component.onCompleted: { console.log(index) } } }
gives:
qml: 0 qml: 1 qml: 2 qml: 3 qml: 4 qml: 5 qml: 6 qml: 7 qml: 8 qml: 9
Even without the added index property.
But if I do:
Repeater{ model: randomQuestions delegate: QuizPage{ question: randomQuestions[index] } }
It only works with adding into QuizPage:
required property int index
Otherwise:
qrc:/qml/quiz/QuizPage.qml:52: TypeError: Cannot read property 'id' of undefined qrc:/qml/quiz/QuizPage.qml:57: TypeError: Cannot read property 'askedQuestion' of undefined qrc:/qml/quiz/QuizPage.qml:64: TypeError: Cannot read property 'picture' of undefined qrc:/qml/quiz/Quiz.qml:0: ReferenceError: index is not defined
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@sandro4912 said in How to create n Objects dynamically to populate StackView:
required property int index
Why are you doing this? This makes zero sense to create a require property when all your info is in your question property.
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@sandro4912 said in How to create n Objects dynamically to populate StackView:
question.answer1
Also, for every usage of question inside of QuizPage do this:
Change this:
question.answer1
To this:
root.question.answer1I think you may be having scoping issues with the question property.
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check out this:
https://stackoverflow.com/questions/62484078/required-property-not-working-with-repeater
The issue is if you have a required property in an item you put into an repeater it only gets access to the index in the weired way that you add an index as required property. I also don't understand why it is necessary.
You can try it out by copy the project on git hub and remove the line index:
https://github.com/SandroWissmann/Quiz -
The problem they had is that you have to use the delegate property to get access to the properties the Repeater adds to the delegate.
If the "required" part makes it not work, then get rid of it.
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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.
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Of course I could change
required property var question
to
property var question
but 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 index
looks like a workarround.
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@fcarney
you are right it does not work anymore. I will check that issue tomorrow and then come back to here. -
@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.
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@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 saiddelegate
is 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
index
ormodelData
if 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
QQmlListProperty
is 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*>
,QVariantList
or even betterQAbstractListModel
if you need a dynamic model.QQmlListProperty
does work, but it's not its job. -
@GrecKo
No wonder I was going crazy trying to understand this problem. Thanks for shedding light on this. -
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
QSortFilterProxModel
which picks um the required random questions to expose that to QML?