QQmlEngine Class

See also https://, https://, https://

This property holds the directory for storing offline user data

Returns the directory where SQL and other offline storage is placed.

The SQL databases created with openDatabase() are stored here.

The default is QML/OfflineStorage in the platform-standard user application data directory.

Note that the path may not currently exist on the filesystem, so callers wanting to create new files at this location should create it first - see https://().

Access functions:

• offlineStoragePath() const

• void setOfflineStoragePath(const &dir)

Create a new https:// with the given parent.

Destroys the https://.

Any https://'s created on this engine will be invalidated, but not destroyed (unless they are parented to the https:// object).

See https:// docs for details on cleaning up the JS engine.

Sets the provider to use for images requested via the image: url scheme, with host providerId. The https:// takes ownership of provider.

Image providers enable support for pixmap and threaded image requests. See the https:// documentation for details on implementing and using image providers.

All required image providers should be added to the engine before any QML sources files are loaded.

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Adds path as a directory where the engine searches for installed modules in a URL-based directory structure.

The path may be a local filesystem directory, a https:// path (:/imports), a https:// url (qrc:/imports) or a URL.

The path will be converted into canonical form before it is added to the import path list.

The newly added path will be first in the https://().

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Adds path as a directory where the engine searches for native plugins for imported modules (referenced in the qmldir file).

By default, the list contains only ., i.e. the engine searches in the directory of the qmldir file itself.

The newly added path will be first in the https://().

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Adds a urlInterceptor to be used when resolving URLs in QML. This also applies to URLs used for loading script files and QML types. The URL interceptors should not be modifed while the engine is loading files, or URL selection may be inconsistent. Multiple URL interceptors, when given, will be called in the order they were added for each URL.

https:// does not take ownership of the interceptor and won't delete it.

Return the base URL for this engine. The base URL is only used to resolve components when a relative URL is passed to the https:// constructor.

If a base URL has not been explicitly set, this method returns the application's current working directory.

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Clears the engine's internal component cache.

This function causes the property metadata of all components previously loaded by the engine to be destroyed. All previously loaded components and the property bindings for all extant objects created from those components will cease to function.

This function returns the engine to a state where it does not contain any loaded component data. This may be useful in order to reload a smaller subset of the previous component set, or to load a new version of a previously loaded component.

Once the component cache has been cleared, components must be loaded before any new objects can be created.

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Returns the https:// for the object, or 0 if no context has been set.

When the https:// instantiates a https://, the context is set automatically.

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Reimplements: https://.

This signal is emitted when the QML loaded by the engine would like to exit from the event loop with the specified return code retCode.

This function was introduced in Qt 5.8.

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Returns the image provider set for providerId if found; otherwise returns nullptr.

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Returns the list of directories where the engine searches for installed modules in a URL-based directory structure.

For example, if /opt/MyApp/lib/imports is in the path, then QML that imports com.mycompany.Feature will cause the https:// to look in /opt/MyApp/lib/imports/com/mycompany/Feature/ for the components provided by that module. A qmldir file is required for defining the type version mapping and possibly QML extensions plugins.

By default, the list contains the directory of the application executable, paths specified in the QML2_IMPORT_PATH environment variable, and the builtin Qml2ImportsPath from https://.

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Imports the plugin named filePath with the uri provided. Returns true if the plugin was successfully imported; otherwise returns false.

On failure and if non-null, the errors list will have any errors which occurred prepended to it.

The plugin has to be a Qt plugin which implements the https:// interface.

Returns the currently set incubation controller, or 0 if no controller has been set.

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Run the current URL interceptors on the given url of the given type and return the result.

Returns a common https:// which can be used by any QML type instantiated by this engine.

If a https:// has been set and a https:// has not yet been created, the https:// will be used to create the https://; otherwise the returned https:// will have no proxy or cache set.

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Returns the current https://.

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Returns the file path where a https:// database with the identifier databaseName is (or would be) located.

This function was introduced in Qt 5.9.

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Returns true if warning messages will be output to stderr in addition to being emitted by the https://() signal, otherwise false.

The default value is true.

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Returns the list of directories where the engine searches for native plugins for imported modules (referenced in the qmldir file).

By default, the list contains only ., i.e. the engine searches in the directory of the qmldir file itself.

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This signal is emitted when the QML loaded by the engine would like to quit.

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Removes the image provider for providerId.

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Remove a urlInterceptor that was previously added using https://. The URL interceptors should not be modifed while the engine is loading files, or URL selection may be inconsistent.

This does not delete the interceptor, but merely removes it from the engine. You can re-use it on the same or a different engine afterwards.

Refreshes all binding expressions that use strings marked for translation.

Call this function after you have installed a new translator with https://, to ensure that your user-interface shows up-to-date translations.

This function was introduced in Qt 5.10.

Returns the engine's root context.

The root context is automatically created by the https://. Data that should be available to all QML component instances instantiated by the engine should be put in the root context.

Additional data that should only be available to a subset of component instances should be added to sub-contexts parented to the root context.

Set the base URL for this engine to url.

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Sets the https:// for the object to context. If the object already has a context, a warning is output, but the context is not changed.

When the https:// instantiates a https://, the context is set automatically.

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Sets paths as the list of directories where the engine searches for installed modules in a URL-based directory structure.

By default, the list contains the directory of the application executable, paths specified in the QML2_IMPORT_PATH environment variable, and the builtin Qml2ImportsPath from https://.

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Sets the engine's incubation controller. The engine can only have one active controller and it does not take ownership of it.

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Sets the factory to use for creating https://(s).

https:// is used for all network access by QML. By implementing a factory it is possible to create custom https:// with specialized caching, proxy and cookie support.

The factory must be set before executing the engine.

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Set whether warning messages will be output to stderr to enabled.

If enabled is true, any warning messages generated by QML will be output to stderr and emitted by the https://() signal. If enabled is false, only the https://() signal will be emitted. This allows applications to handle warning output themselves.

The default value is true.

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Sets the list of directories where the engine searches for native plugins for imported modules (referenced in the qmldir file) to paths.

By default, the list contains only ., i.e. the engine searches in the directory of the qmldir file itself.

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Returns the instance of a singleton type that was registered under qmlTypeId.

The template argument T may be either https:// or a pointer to a https://-derived type and depends on how the singleton was registered. If no instance of T has been created yet, it is created now. If qmlTypeId does not represent a valid singleton type, either a default constructed https:// or a nullptr is returned.

https://* example:

class MySingleton : public QObject {
    Q_OBJECT

    // Register as default constructed singleton.
    QML_ELEMENT
    QML_SINGLETON

    static int typeId;
    // ...
};

    MySingleton::typeId = qmlTypeId(...);

    // Retrieve as QObject*
    QQmlEngine engine;
    MySingleton* instance = engine.singletonInstance<MySingleton*>(MySingleton::typeId);

https:// example:

    // Register with QJSValue callback
    int typeId = qmlRegisterSingletonType(...);

    // Retrieve as QJSValue
    QQmlEngine engine;
    QJSValue instance = engine.singletonInstance<QJSValue>(typeId);

It is recommended to store the QML type id, e.g. as a static member in the singleton class. The lookup via https://() is costly.

This function was introduced in Qt 5.12.

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Trims the engine's internal component cache.

This function causes the property metadata of any loaded components which are not currently in use to be destroyed.

A component is considered to be in use if there are any extant instances of the component itself, any instances of other components that use the component, or any objects instantiated by any of those components.

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This signal is emitted when warnings messages are generated by QML.

The form of this template function is:

template<typename T> QObject *qmlAttachedPropertiesObject(const QObject *attachee, bool create = true)

This returns the attached object instance that has been attached to the specified attachee by the attaching type T.

If create is true and type T is a valid attaching type, this creates and returns a new attached object instance.

Returns 0 if type T is not a valid attaching type, or if create is false and no attachment object instance has previously been created for attachee.

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Clears all stored type registrations, such as those produced with https://().

Do not call this function while a https:// exists or behavior will be undefined. Any existing QQmlEngines must be deleted before calling this function. This function only affects the application global cache. Delete the https:// to clear all cached data relating to that engine.

Returns the https:// associated with object, if any. This is equivalent to https://(object).

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Prints debug messages that include the file and line number for the specified QML object.

When QML types produce logging messages, it improves traceability if they include the QML file and line number on which the particular instance was instantiated.

To include the file and line number, an object must be passed. If the file and line number is not available for that instance (either it was not instantiated by the QML engine or location information is disabled), "unknown location" will be used instead. For example,

qmlDebug(object) << "Internal state: 42";

prints

QML MyCustomType (unknown location): Internal state: 42

This function was introduced in Qt 5.9.

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Returns the https:// associated with object, if any. This is equivalent to https://(object)->engine(), but more efficient.

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Prints informational messages that include the file and line number for the specified QML object.

When QML types produce logging messages, it improves traceability if they include the QML file and line number on which the particular instance was instantiated.

To include the file and line number, an object must be passed. If the file and line number is not available for that instance (either it was not instantiated by the QML engine or location information is disabled), "unknown location" will be used instead.

For example,

qmlInfo(object) << tr("component property is a write-once property");

prints

QML MyCustomType (unknown location): component property is a write-once property

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This function protects a module from having types registered into it. This can be used to prevent other plugins from injecting types into your module. It can also be a performance improvement, as it allows the engine to skip checking for the possibility of new types or plugins when this import is reached.

The performance benefit is primarily seen when registering application specific types from within the application instead of through a plugin. Using qmlProtectModule allows the engine to skip checking for a plugin when that uri is imported, which can be noticeable with slow file systems.

After this function is called, any attempt to register C++ types into this uri, major version combination will lead to a runtime error. Call this after you have registered all of your types with the engine.

Returns true if the module with uri as a https:// and majVersion as a major version number was found and locked, otherwise returns false. The module must contain exported types in order to be found.

This template function registers the C++ type in the QML system as an anonymous type. The resulting QML type does not have a name. Therefore, instances of this type cannot be created from the QML system. You can, however, access instances of the type when they are exposed as properties of other types.

Use this function when the type will not be referenced by name, specifically for C++ types that are used on the left-hand side of a property binding. To indicate to which module the type belongs use uri and versionMajor.

For example, consider the following two classes:

class Bar : public QObject
{
    Q_OBJECT
    Q_PROPERTY(QString baz READ baz WRITE setBaz NOTIFY bazChanged)

public:
    Bar() {}

    QString baz() const { return mBaz; }

    void setBaz(const QString &baz)
    {
        if (baz == mBaz)
            return;

        mBaz = baz;
        emit bazChanged();
    }

signals:
    void bazChanged();

private:
    QString mBaz;
};

class Foo : public QObject
{
    Q_OBJECT
    Q_PROPERTY(Bar *bar READ bar CONSTANT FINAL)

public:
    Foo() {}

    Bar *bar() { return &mBar; }

private:
    Bar mBar;
};

In QML, we assign a string to the baz property of bar:

Foo {
    bar.baz: "abc"
    Component.onCompleted: print(bar.baz)
}

For the QML engine to know that the Bar type has a baz property, we have to make Bar known:

qmlRegisterType<Foo>("App", 1, 0, "Foo");
qmlRegisterAnonymousType<Bar>("App", 1);

As the Foo type is instantiated in QML, it must be registered with the version of https://() that takes an element name.

Returns the QML type id.

This function was introduced in Qt 5.14.

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This template function registers the C++ type and its extension object in the QML system with the name qmlName in the library imported from uri having version number composed from versionMajor and versionMinor. Properties not available in the main type will be searched for in the extension object.

Returns the QML type id.

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This template function registers the C++ type and its extension in the QML system with the name qmlName in the library imported from uri having version number composed from versionMajor and versionMinor.

While the type has a name and a type, it cannot be created. An error message with the given reason is printed if the user attempts to create an instance of this type.

This is useful where the type is only intended for providing attached properties, enum values or an abstract base class with its extension.

Returns the QML type id.

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This function registers a module in a particular uri with a version specified in versionMajor and versionMinor.

This can be used to make a certain module version available, even if no types are registered for that version. This is particularly useful for keeping the versions of related modules in sync.

This function was introduced in Qt 5.9.

This template function registers the specified revision of a C++ type in the QML system with the library imported from uri having the version number composed from versionMajor and versionMinor.

Returns the QML type id.

template<typename T, int metaObjectRevision>
int qmlRegisterRevision(const char *uri, int versionMajor, int versionMinor);

This function is typically used to register the revision of a base class to use for the specified version of the type (see https://).

This function is used to register a singleton object cppObject, with a particular uri and typeName. Its version is a combination of versionMajor and versionMinor.

Installing a singleton type into a URI allows you to provide arbitrary functionality (methods and properties) to QML code without requiring individual instances of the type to be instantiated by the client.

Use this function to register an object of the given type T as a singleton type.

A https:// singleton type may be referenced via the type name with which it was registered; in turn this type name may be used as the target in a https:// type, or like any other type ID. However, there's one exception: a https:// singleton type property can't be aliased because the singleton type name does not identify an object within the same component as any other item.

Usage:

// First, define your QObject which provides the functionality.
class SingletonTypeExample : public QObject
{
    Q_OBJECT
    Q_PROPERTY(int someProperty READ someProperty WRITE setSomeProperty NOTIFY somePropertyChanged)

public:
    explicit SingletonTypeExample(QObject* parent = nullptr) : QObject(parent) {}

    Q_INVOKABLE int doSomething()
    {
        setSomeProperty(5);
        return m_someProperty;
    }

    int someProperty() const { return m_someProperty; }
    void setSomeProperty(int val) {
        if (m_someProperty != val) {
            m_someProperty = val;
            emit somePropertyChanged(val);
        }
    }

signals:
    void somePropertyChanged(int newValue);

private:
    int m_someProperty = 0;
};

// Second, create an instance of the object

// allocate example before the engine to ensure that it outlives it
QScopedPointer<SingletonTypeExample> example(new SingletonTypeExample);
QQmlEngine engine;

// Third, register the singleton type provider with QML by calling this
// function in an initialization function.
qmlRegisterSingletonInstance("Qt.example.qobjectSingleton", 1, 0, "MyApi", example.get());

In order to use the registered singleton type in QML, you must import the URI with the corresponding version.

import QtQuick 2.0
import Qt.example.qobjectSingleton 1.0
Item {
    id: root
    property int someValue: MyApi.someProperty

    Component.onCompleted: {
        console.log(MyApi.doSomething())
    }
}

This function was introduced in Qt 5.14.

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This function may be used to register a singleton type provider callback in a particular uri and typeName with a version specified in versionMajor and versionMinor.

Installing a singleton type allows developers to provide arbitrary functionality (methods and properties) to a client without requiring individual instances of the type to be instantiated by the client.

A singleton type may be either a https:// or a https://. This function should be used to register a singleton type provider function which returns a https:// as a singleton type.

NOTE: https:// singleton type properties will not trigger binding re-evaluation if changed.

Usage:

// First, define the singleton type provider function (callback).
static QJSValue example_qjsvalue_singletontype_provider(QQmlEngine *engine, QJSEngine *scriptEngine)
{
    Q_UNUSED(engine)

    static int seedValue = 5;
    QJSValue example = scriptEngine->newObject();
    example.setProperty("someProperty", seedValue++);
    return example;
}

// Second, register the singleton type provider with QML by calling this function in an initialization function.
qmlRegisterSingletonType("Qt.example.qjsvalueApi", 1, 0, "MyApi", example_qjsvalue_singletontype_provider);

Alternatively, you can use a C++11 lambda:

qmlRegisterSingletonType("Qt.example.qjsvalueApi", 1, 0, "MyApi", [](QQmlEngine *engine, QJSEngine *scriptEngine) -> QJSValue {
    Q_UNUSED(engine)

    static int seedValue = 5;
    QJSValue example = scriptEngine->newObject();
    example.setProperty("someProperty", seedValue++);
    return example;
});

In order to use the registered singleton type in QML, you must import the singleton type.

import QtQuick 2.0
import Qt.example.qjsvalueApi 1.0 as ExampleApi
Item {
    id: root
    property int someValue: ExampleApi.MyApi.someProperty
}

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This function may be used to register a singleton type provider callback in a particular uri and typeName with a version specified in versionMajor and versionMinor.

Installing a singleton type into a uri allows developers to provide arbitrary functionality (methods and properties) to clients without requiring individual instances ot the type to be instantiated by the client.

A singleton type may be either a https:// or a https://. This function should be used to register a singleton type provider function which returns a https:// of the given type T as a singleton type.

A https:// singleton type may be referenced via the type name with which it was registered, and this typename may be used as the target in a https:// type or otherwise used as any other type id would. One exception to this is that a https:// singleton type property may not be aliased.

NOTE: A https:// singleton type instance returned from a singleton type provider is owned by the QML engine unless the object has explicit QQmlEngine::CppOwnership flag set.

Usage:

// First, define your QObject which provides the functionality.
class SingletonTypeExample : public QObject
{
    Q_OBJECT
    Q_PROPERTY (int someProperty READ someProperty WRITE setSomeProperty NOTIFY somePropertyChanged)

public:
    SingletonTypeExample(QObject* parent = 0)
        : QObject(parent), m_someProperty(0)
    {
    }

    ~SingletonTypeExample() {}

    Q_INVOKABLE int doSomething() { setSomeProperty(5); return m_someProperty; }

    int someProperty() const { return m_someProperty; }
    void setSomeProperty(int val) { m_someProperty = val; emit somePropertyChanged(val); }

signals:
    void somePropertyChanged(int newValue);

private:
    int m_someProperty;
};

// Second, define the singleton type provider function (callback).
static QObject *example_qobject_singletontype_provider(QQmlEngine *engine, QJSEngine *scriptEngine)
{
    Q_UNUSED(engine)
    Q_UNUSED(scriptEngine)

    SingletonTypeExample *example = new SingletonTypeExample();
    return example;
}

// Third, register the singleton type provider with QML by calling this function in an initialization function.
qmlRegisterSingletonType<SingletonTypeExample>("Qt.example.qobjectSingleton", 1, 0, "MyApi", example_qobject_singletontype_provider);

Alternatively, you can use a C++11 lambda:

qmlRegisterSingletonType<SingletonTypeExample>("Qt.example.qobjectSingleton", 1, 0, "MyApi", [](QQmlEngine *engine, QJSEngine *scriptEngine) -> QObject * {
    Q_UNUSED(engine)
    Q_UNUSED(scriptEngine)

    SingletonTypeExample *example = new SingletonTypeExample();
    return example;
});

In order to use the registered singleton type in QML, you must import the singleton type.

import QtQuick 2.0
import Qt.example.qobjectSingleton 1.0
Item {
    id: root
    property int someValue: MyApi.someProperty

    Component.onCompleted: {
        someValue = MyApi.doSomething()
    }
}

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This function overloads https://.

This function was introduced in Qt 5.14.

This function may be used to register a singleton type with the name qmlName, in the library imported from uri having the version number composed from versionMajor and versionMinor. The type is defined by the QML file located at url. The url must be an absolute URL, i.e. url.isRelative() == false.

In addition the type's QML file must have pragma Singleton statement among its import statements.

A singleton type may be referenced via the type name with which it was registered, and this typename may be used as the target in a https:// type or otherwise used as any other type id would. One exception to this is that a singleton type property may not be aliased (because the singleton type name does not identify an object within the same component as any other item).

Usage:

// First, define your QML singleton type which provides the functionality.
pragma Singleton
import QtQuick 2.0
Item {
    property int testProp1: 125
}

// Second, register the QML singleton type by calling this function in an initialization function.
qmlRegisterSingletonType(QUrl("file:///absolute/path/SingletonType.qml"), "Qt.example.qobjectSingleton", 1, 0, "RegisteredSingleton");

In order to use the registered singleton type in QML, you must import the singleton type.

import QtQuick 2.0
import Qt.example.qobjectSingleton 1.0
Item {
    id: root
    property int someValue: RegisteredSingleton.testProp1
}

It is also possible to have QML singleton types registered without using the https:// function. That can be done by adding a pragma Singleton statement among the imports of the type's QML file. In addition the type must be defined in a qmldir file with a singleton keyword and the qmldir must be imported by the QML files using the singleton.

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This template function registers the C++ type in the QML system with the name qmlName, in the library imported from uri having the version number composed from versionMajor and versionMinor.

Returns the QML type id.

There are two forms of this template function:

template<typename T>
int qmlRegisterType(const char *uri, int versionMajor, int versionMinor, const char *qmlName);

template<typename T, int metaObjectRevision>
int qmlRegisterType(const char *uri, int versionMajor, int versionMinor, const char *qmlName);

The former is the standard form which registers the type T as a new type. The latter allows a particular revision of a class to be registered in a specified version (see https://).

For example, this registers a C++ class MySliderItem as a QML type named Slider for version 1.0 of a type namespace called "com.mycompany.qmlcomponents":

qmlRegisterType<MySliderItem>("com.mycompany.qmlcomponents", 1, 0, "Slider");

Once this is registered, the type can be used in QML by importing the specified type namespace and version number:

import com.mycompany.qmlcomponents 1.0

Slider {
    // ...
}

Note that it's perfectly reasonable for a library to register types to older versions than the actual version of the library. Indeed, it is normal for the new library to allow QML written to previous versions to continue to work, even if more advanced versions of some of its types are available.

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This function registers a type in the QML system with the name qmlName, in the library imported from uri having the version number composed from versionMajor and versionMinor. The type is defined by the QML file located at url. The url must be an absolute URL, i.e. url.isRelative() == false.

Normally QML files can be loaded as types directly from other QML files, or using a qmldir file. This function allows registration of files to types from C++ code, such as when the type mapping needs to be procedurally determined at startup.

Returns -1 if the registration was not successful.

This function registers a type in the QML system with the name qmlName, in the type namespace imported from uri having the version number composed from versionMajor and versionMinor, but any attempt to instantiate the type will produce the given error message.

Normally, the types exported by a plugin should be fixed. However, if a C++ type is not available, you should at least "reserve" the QML type name, and give the user of the unavailable type a meaningful error message.

Returns the QML type id.

Example:

#ifdef NO_GAMES_ALLOWED
qmlRegisterTypeNotAvailable("MinehuntCore", 0, 1, "Game", "Get back to work, slacker!");
#else
qmlRegisterType<MinehuntGame>("MinehuntCore", 0, 1, "Game");
#endif

This will cause any QML which imports the "MinehuntCore" type namespace and attempts to use the type to produce an error message:

fun.qml: Get back to work, slacker!
   Game {
   ^

Without this, a generic "Game is not a type" message would be given.

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This function registers the staticMetaObject and its extension in the QML system with the name qmlName in the library imported from uri having version number composed from versionMajor and versionMinor.

An instance of the meta object cannot be created. An error message with the given reason is printed if the user attempts to create it.

This function is useful for registering https:// namespaces.

Returns the QML type id.

For example:

namespace MyNamespace {
  Q_NAMESPACE
  enum MyEnum {
      Key1,
      Key2,
  };
  Q_ENUMS(MyEnum)
}

//...
qmlRegisterUncreatableMetaObject(MyNamespace::staticMetaObject, "io.qt", 1, 0, "MyNamespace", "Access to enums & flags only");

On the QML side, you can now use the registered enums:

Component.onCompleted: console.log(MyNamespace.Key2)

This function was introduced in Qt 5.8.

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This template function registers the C++ type in the QML system with the name qmlName, in the library imported from uri having the version number composed from versionMajor and versionMinor.

While the type has a name and a type, it cannot be created, and the given error message will result if creation is attempted.

This is useful where the type is only intended for providing attached properties or enum values.

Returns the QML type id.

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Returns the QML type id of a type that was registered with the name qmlName in a particular uri and a version specified in versionMajor and versionMinor.

This function returns the same value as the QML type registration functions such as https://() and https://().

If qmlName, uri and versionMajor match a registered type, but the specified minor version in versionMinor is higher, then the id of the type with the closest minor version is returned.

Returns -1 if no matching type was found or one of the given parameters was invalid.

This function was introduced in Qt 5.12.

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Prints warning messages that include the file and line number for the specified QML object.

When QML types produce logging messages, it improves traceability if they include the QML file and line number on which the particular instance was instantiated.

To include the file and line number, an object must be passed. If the file and line number is not available for that instance (either it was not instantiated by the QML engine or location information is disabled), "unknown location" will be used instead.

For example,

qmlInfo(object) << tr("property cannot be set to 0");

prints

QML MyCustomType (unknown location): property cannot be set to 0

This function was introduced in Qt 5.9.

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Declares that the enclosing type or namespace was added in the specified minor VERSION, relative to the module major version. The minor version is assumed to be in line with any revisions given by https://() macros on methods, slots, or signals, and any REVISION tags on properties declared with https://().

https://() only takes effect if the type or namespace is available in QML, by having a QML_ELEMENT, https://(), https://, or https:// macro.

If the QML module the type belongs to is imported with a lower version than the one determined this way, the QML type is invisible.

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Declares the enclosing type to be available, but anonymous in QML. The type cannot be created or used as property type, but when passed from C++, it is recognized.

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Declares that the enclosing type attaches ATTACHED_TYPE as an https:// to other types. This takes effect if the type is exposed to QML using a https:// or https://() macro.

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Equivalent to Q_DECLARE_METATYPE(TYPE *) and Q_DECLARE_METATYPE(QQmlListProperty<TYPE>)

Declares additional properties of the given Type as described by the specified Flags.

Current the only supported type info is QML_HAS_ATTACHED_PROPERTIES which declares that the Type supports https://. QML_DECLARE_TYPEINFO() is not necessary if Type contains the https:// macro.

Declares the enclosing type or namespace to be available in QML, using its class or namespace name as the QML element name.

For example, this makes the C++ class Slider available as a QML type named Slider.

class Slider : public QObject
{
    Q_OBJECT
    QML_ELEMENT
    ...
}

You can use the build system to register the type in the type namespace com.mycompany.qmlcomponents with major version 1 by specifying the following in your project file:

CONFIG += qmltypes
QML_IMPORT_NAME = com.mycompany.qmlcomponents
QML_IMPORT_MAJOR_VERSION = 1

Once registered, the type can be used in QML by importing the same type namespace and version number:

import com.mycompany.qmlcomponents 1.0

Slider {
    // ...
}

You can also make namespaces tagged with https:// available this way, in order to expose any enums tagged with https:// they contain.

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Declares that the enclosing type uses EXTENDED_TYPE as an extension to provide further properties, methods, and enumerations in QML. This takes effect if the type is exposed to QML using a https:// or https://() macro.

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Declares that the enclosing type uses EXTENDED_NAMESPACE as an extension to provide further enumerations in QML. This takes effect if the type is exposed to QML using a https:// or https://() macro.

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Declares that any https://, https://(), https://, https://, https://(), https://, https://(), https://(), https://(), https://(), or https://() macros in the enclosing C++ type do not apply to the enclosing type but instead to FOREIGN_TYPE. The enclosing type still needs to be registered with the https:// using a https:// or https:// macro.

This is useful for registering types that cannot be amended to add the macros, for example because they belong to 3rdparty libraries. To register a namespace, see https://().

NOTE: You may want to use https://() instead of https:// due to the fact that the element will be named like the struct it is contained in, not the foreign type. See https:// for an example.

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Declares that any https://, https://(), https://, https://, https://(), https://, https://(), or https://() macros in the enclosing C++ namespace do not apply to the enclosing type but instead to FOREIGN_NAMESPACE. The enclosing namespace still needs to be registered with the https:// using a https:// macro.

This is useful for registering namespaces that cannot be amended to add the macros, for example because they belong to 3rdparty libraries.

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This macro tells Qt which QML interfaces the class implements. This macro should only be used for interfacing with classes using https://, use https:// otherwise. It's required in order for declarative registration via https:// to function properly.

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This macro registers the enclosing C++ type in the QML system as an interface.

Types registered as an interface in QML should also declare themselves as an interface with the https://. For example:

struct FooInterface
{
    QML_INTERFACE
public:
    virtual ~FooInterface();
    virtual void doSomething() = 0;
};

Q_DECLARE_INTERFACE(FooInterface, "org.foo.FooInterface")

When registered with QML in this way, they can be used as property types:

https://(FooInterface *foo READ foo WRITE setFoo)

When you assign a https:// sub-class to this property, the QML engine does the interface cast to FooInterface* automatically.

Interface types are implicitly anonymous and uncreatable in QML.

NOTE: When inheriting from types using QML_INTERFACE, use https:// instead of https://.

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Declares the enclosing type or namespace to be available in QML, using name as the element name. Otherwise behaves the same as https://.

class SqlEventDatabase : public QObject
{
    Q_OBJECT
    QML_NAMED_ELEMENT(EventDatabase)

    // ...
};

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Declares that the enclosing type or namespace was removed in the specified minor VERSION, relative to the module major version. This is primarily useful when replacing the implementation of a QML type. If a corresponding https://() is present on a different type or namespace of the same QML name, then the removed type is used when importing versions of the module lower than VERSION, and the added type is used when importing versions of the module greater or equal VERSION.

https://() only takes effect if type or namespace is available in QML, by having a QML_ELEMENT, https://(), https://, or https:// macro.

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Declares the enclosing type to be a singleton in QML. This only takes effect if the type is a https:// and is available in QML (by having a https:// or https://() macro). By default, each https:// will try to create a singleton instance using either the type's default constructor or a static factory function of the signature T *create(QQmlEngine *, QJSEngine *) when the type is first accessed. If both do exist and are accessible, the default constructor is preferred. If there is no default constructor and no factory function the singleton is initially inaccessible. This behavior can be overridden by calling https://() with a specific (external) factory function or https://() with a specific instance for the same class and the same type namespace and version.

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This macro declares the enclosing type to be unavailable in QML. It registers an internal dummy type called QQmlTypeNotAvailable as https://() type, using any further QML macros you specify.

Normally, the types exported by a module should be fixed. However, if a C++ type is not available, you should at least "reserve" the QML type name, and give the user of the unavailable type a meaningful error message.

Example:

#ifdef NO_GAMES_ALLOWED
struct MinehuntGame
{
    Q_GADGET
    QML_NAMED_ELEMENT(Game)
    QML_UNAVAILABLE
    QML_UNCREATABLE("Get back to work, slacker!");
};
#else
class MinehuntGame : public QObject
{
    Q_OBJECT
    QML_NAMED_ELEMENT(Game)
    // ...
};
#endif

This will cause any QML which attempts to use the "Game" type to produce an error message:

fun.qml: Get back to work, slacker!
   Game {
   ^

Using this technique, you only need a https:// struct to customize the error message, not a full-blown https://. Without https://(), QML_UNAVAILABLE still results in a more specific error message than the usual "is not a type" for completely unknown types.

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Declares that the enclosing type shall not be creatable from QML. This takes effect if the type is available in QML, by having a https:// or https://() macro. The reason will be emitted as error message if an attempt to create the type from QML is detected.

Some QML types are implicitly uncreatable, in particular types exposed with https:// or namespaces exposed with https:// or https://(). For such types, QML_UNCREATABLE() can be used to provide a custom error message.

Since Qt 6.0 you can use "" instead of a reason to use a standard message instead.

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