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C

Singleton Struct

template <typename T> struct Qul::Singleton

Inherit from this class to expose the C++ class or struct to the QML as a singleton. More...

Header: #include <qul/singleton.h>
Since: Qt Quick Ultralite 1.0
Inherits: Qul::Object and Qul::SingletonBase

Static Public Members

T &instance()

Detailed Description

The qmlinterfacegenerator tool will generate QML type with pragma Singleton directive for a class derived from the singleton.

This class use the Curiously recurring template pattern (CRTP) and the template parameter needs to be the derived type.

Minimal example:

struct MySingleton : public Qul::Singleton<MySingleton>
{
    Property<int> someProperty;
    int someFunction(int param);
};

Above example is just fine if you are not going to use Singleton from C++ code. Otherwise you should make it a bit more complete:

struct MySingleton : Qul::Singleton<MySingleton>
{
    // Create friendship for a base class to be able to access private constructor
    friend struct Qul::Singleton<MySingleton>

    Property<int> someProperty;
    int someFunction(int param);

private:
    MySingleton() {}                                // Private constructor
    MySingleton(const MySingleton &);              // Non copy-constructible
    MySingleton &operator=(const MySingleton &);   // Non copyable
};

Now MySingleton can be safely used both form QML:

Item {
    property int otherProperty: MySingleton.someProperty
}

and from C++:

void someFunction() {
    MySingleton::instance().someProperty.setValue(42);
}

See also Singletons and Defining Singletons in QML.

Member Function Documentation

[static] T &Singleton::instance()

Returns a reference to the singleton instance.

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