src_qml_qqmlengine.cpp

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// Copyright (C) 2020 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
 
//! [0]
class MySingleton : public QObject {
    Q_OBJECT
 
    // Register as default constructed singleton.
    QML_ELEMENT
    QML_SINGLETON
 
    static int typeId;
    // ...
};
//! [0]
 
/*
//! [1]
    MySingleton::typeId = qmlTypeId(...);
//! [1]
*/
 
void wrapper2() {
//! [2]
    // Retrieve as QObject*
    QQmlEngine engine;
    MySingleton* instance = engine.singletonInstance<MySingleton*>(MySingleton::typeId);
//! [2]
}
 
/*
//! [3]
    // Register with QJSValue callback
    int typeId = qmlRegisterSingletonType(...);
//! [3]
*/
 
void wrapper4(int typeId) {
//! [4]
    // Retrieve as QJSValue
    QQmlEngine engine;
    QJSValue instance = engine.singletonInstance<QJSValue>(typeId);
//! [4]
}
 
void wrapper5() {
//! [5]
    QQmlEngine engine;
    MySingleton *singleton = engine.singletonInstance<MySingleton *>("mymodule", "MySingleton");
//! [5]
}
 
class BackendService {};
 
//! [6]
class CppSingleton: public QObject {
    Q_OBJECT
    QML_ELEMENT
    QML_SINGLETON
    QML_UNCREATABLE("Provided via QQmlEngine::setExternalSingletonInstance")
    // Q_PROPERTY(...)
public:
    explicit CppSingleton(BackendService *service); // constructor taking a reference to something MySingleton needs
    // members, Q_INVOKABLE functions, etc.
};
//! [6]
 
void wrapper6() {
//! [7]
    // create and setup the backend service
    BackendService service;
 
    // create your singleton instance
    CppSingleton singleton(&service);
    QQmlApplicationEngine engine;
    engine.setExternalSingletonInstance("com.company.myApp", "MySingleton", &singleton);
    engine.loadFromModule("com.company.myApp", "Main");
//! [7]
}