QML Context lost when QML component is created from C++

[MarcVanDaele]

Hello,

I have a simple C++ QQuickItem component that instantiates a QQmlComponent.
But within the instantiated QQmlComponent, the ids of other QML components are not known anymore (see detailed example below)
Apparently, the context is lost.

The resulting log shows

qrc:/main.qml:35: ReferenceError: textId is not defined
qml: Text(not delegate)=Hello World

Is this something I can fix? Or is this 'logical'/'explainable' somehow?

The example code below illustrates the problem and consists of

• main.cpp
• MyQuickComponent.h
• MyQuickComponent.cpp
• main.qml

Thanks in advance,

Marc
main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include "myquickcomponent.h"

QQmlApplicationEngine *engine;

int main(int argc, char *argv[])
{
    qmlRegisterType<MyQuickComponent>("Mine", 1, 0, "MyQuickComponent");
    QGuiApplication app(argc, argv);

    engine = new QQmlApplicationEngine();
    engine->load(QUrl(QStringLiteral("qrc:/main.qml")));

    return app.exec();
}

MyQuickComponent.h

#ifndef MYQUICKCOMPONENT_H
#define MYQUICKCOMPONENT_H
#include <QQuickPaintedItem>
#include <QPainter>

class MyQuickComponent : public QQuickPaintedItem
{
Q_OBJECT
    Q_PROPERTY(QQmlComponent *delegate READ delegate WRITE setDelegate NOTIFY delegateChanged)

public:
    MyQuickComponent(QQuickItem *parent = 0);
    void paint(QPainter *painter);

    QQmlComponent *delegate() const { return m_delegate; }
    void setDelegate(QQmlComponent *delegate);


Q_SIGNALS:
    void delegateChanged();

private:
    QQmlComponent *m_delegate;

};

#endif // MYQUICKCOMPONENT_H

MyQuickComponent.cpp

#include <QQmlApplicationEngine>
#include <QQmlContext>
#include "myquickcomponent.h"

MyQuickComponent::MyQuickComponent(QQuickItem *parent)
: QQuickPaintedItem(parent), m_delegate(NULL)
{
}

void MyQuickComponent::paint(QPainter *painter)
{
}

extern QQmlApplicationEngine *engine;
void MyQuickComponent::setDelegate(QQmlComponent *delegate)
{
    if (delegate != m_delegate) {
        m_delegate = delegate;
        emit delegateChanged();
    }

    //create object
    QQmlContext *context = new QQmlContext(engine->rootContext());
    context->setContextObject(this);
    QQuickItem *object = qobject_cast<QQuickItem*>(m_delegate->create(context));
    //QQuickItem *object = qobject_cast<QQuickItem*>(m_delegate->beginCreate(engine->rootContext()));
    QQmlEngine::setObjectOwnership(object, QQmlEngine::CppOwnership);
    object->setParentItem(this);
    object->setParent(this);
    object->setProperty("color", "red");
    object->setProperty("y", 200);
    //m_delegate->completeCreate();

}

And finally main.qml

import QtQuick 2.5
import QtQuick.Window 2.2

import Mine 1.0

Window {
    visible: true
    width:600
    height: 600

    Text {
        id: textId
        text: qsTr("Hello World")
        anchors.centerIn: parent
    }

    Rectangle {
        width:100
        height:100
        id: notdelegate
        //here I can access textId
        Component.onCompleted: console.log("Text(not delegate)="+textId.text)
        color: 'green'
    }

    //MyQuickComponent is a C++ QQuickItem that creates the delegate component
    MyQuickComponent {
        width:parent.width
        height: parent.width
        delegate: Rectangle {
            width:100
            height:100
            id: delegate
            //here I can't access textId !!
            Component.onCompleted: console.log("Text(delegate)="+textId.text)
            color: 'green'
        }
    }
}

[dheerendra]

Context actually exist and is not lost. Issue is getting from m_delegate.create(...) call. I don't know why. May be it failed to access the textId due some bug. I verified all the contexts, objects etc. Everything looks fine.

[MarcVanDaele]

Apparently, it was sufficient to replace the line below in MyQuickComponent.cpp

QQmlContext *context = new QQmlContext(engine->rootContext());

with

QQmlContext *context = m_delegate->creationContext();

Note: how can I mark this question as fixed/solved?

[p3c0]

@MarcVanDaele Thanks for sharing the solution.

how can I mark this question as fixed/solved?

Under Topic Tools combobox there's an option as "Mark as Solved". I have marked it now.