class QQmlApplicationEngine¶

QQmlApplicationEngine provides a convenient way to load an application from a single QML file. More…

Synopsis¶

Methods¶

def __init__()
def rootObjects()

Slots¶

def load()
def loadData()
def loadFromModule()
def setExtraFileSelectors()
def setInitialProperties()

Note

This documentation may contain snippets that were automatically translated from C++ to Python. We always welcome contributions to the snippet translation. If you see an issue with the translation, you can also let us know by creating a ticket on https:/bugreports.qt.io/projects/PYSIDE

Detailed Description¶

This class combines a QQmlEngine and QQmlComponent to provide a convenient way to load a single QML file. It also exposes some central application functionality to QML, which a C++/QML hybrid application would normally control from C++.

It can be used like so:

#include <QGuiApplication>
#include <QQmlApplicationEngine>

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);
    QQmlApplicationEngine engine("main.qml");
    return app.exec();
}

Unlike QQuickView, QQmlApplicationEngine does not automatically create a root window. If you are using visual items from Qt Quick, you will need to place them inside of a Window.

You can also use QCoreApplication with QQmlApplicationEngine , if you are not using any QML modules which require a QGuiApplication (such as QtQuick).

List of configuration changes from a default QQmlEngine :

Connecting Qt. quit() to QCoreApplication::quit()

Automatically loads translation files from an i18n directory adjacent to the main QML file.

Translation files must have “qml_” prefix e.g. qml_ja_JP.qm.

Translations are reloaded when the QJSEngine::uiLanguage / Qt.uiLanguage property is changed.

Automatically sets an incubation controller if the scene contains a QQuickWindow.

Automatically sets a QQmlFileSelector as the url interceptor, applying file selectors to all QML files and assets.

The engine behavior can be further tweaked by using the inherited methods from QQmlEngine .

__init__([parent=None])¶

Parameters:: parent – QObject

Create a new QQmlApplicationEngine with the given parent. You will have to call load() later in order to load a QML file.

__init__(filePath[, parent=None])

Parameters:

filePath – str
parent – QObject

Create a new QQmlApplicationEngine and loads the QML file at the given filePath, which must be a local file or qrc path. If a relative path is given then it will be interpreted as relative to the working directory of the application.

This is provided as a convenience, and is the same as using the empty constructor and calling load afterwards.

__init__(url[, parent=None])

Parameters:

url – QUrl
parent – QObject

Create a new QQmlApplicationEngine and loads the QML file at the given url. This is provided as a convenience, and is the same as using the empty constructor and calling load afterwards.

__init__(uri, typeName[, parent=None])

Parameters:

uri – str
typeName – str
parent – QObject

Create a new QQmlApplicationEngine and loads the QML type specified by uri and typeName This is provided as a convenience, and is the same as using the empty constructor and calling loadFromModule afterwards.

load(filePath)¶

Parameters:: filePath – str

Loads the root QML file located at filePath. filePath must be a path to a local file or a path to a file in the resource file system. If filePath is a relative path, it is taken as relative to the application’s working directory. The object tree defined by the file is instantiated immediately.

If an error occurs, error messages are printed with qWarning.

load(url)

Parameters:: url – QUrl

Loads the root QML file located at url. The object tree defined by the file is created immediately for local file urls. Remote urls are loaded asynchronously, listen to the objectCreated signal to determine when the object tree is ready.

If an error occurs, the objectCreated signal is emitted with a null pointer as parameter and error messages are printed with qWarning.

loadData(data[, url=QUrl()])¶

Parameters:

data – QByteArray
url – QUrl

Loads the QML given in data. The object tree defined by data is instantiated immediately.

If a url is specified it is used as the base url of the component. This affects relative paths within the data and error messages.

If an error occurs, error messages are printed with qWarning.

loadFromModule(uri, typeName)¶

Parameters:

uri – str
typeName – str

Loads the QML type typeName from the module specified by uri. If the type originates from a QML file located at a remote url, the type will be loaded asynchronously. Listen to the objectCreated signal to determine when the object tree is ready.

If an error occurs, the objectCreated signal is emitted with a null pointer as parameter and error messages are printed with qWarning.

QQmlApplicationEngine engine;
engine.loadFromModule("QtQuick", "Rectangle");

Note

The module identified by uri is searched in the import path , in the same way as if you were doing import uri inside a QML file. If the module cannot be located there, this function will fail.

See also

loadFromModule

objectCreated(object, url)¶

Parameters:

object – QObject
url – QUrl

This signal is emitted when an object finishes loading. If loading was successful, object contains a pointer to the loaded object, otherwise the pointer is NULL.

The url to the component the object came from is also provided.

Note

If the path to the component was provided as a QString containing a relative path, the url will contain a fully resolved path to the file.

objectCreationFailed(url)¶

Parameters:: url – QUrl

This signal is emitted when loading finishes because an error occurred.

The url to the component that failed to load is provided as an argument.

QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;

// exit on error
QObject::connect(&engine, &QQmlApplicationEngine::objectCreationFailed,
    &app, []() { QCoreApplication::exit(-1); }, Qt::QueuedConnection);
engine.load(QUrl());
return app.exec();

Note

If the path to the component was provided as a QString containing a relative path, the url will contain a fully resolved path to the file.

See also objectCreated , which will be emitted in addition to this signal (even though creation failed).

rootObjects()¶

Return type:: .list of QObject

Returns a list of all the root objects instantiated by the QQmlApplicationEngine . This will only contain objects loaded via load() or a convenience constructor.

Note

In Qt versions prior to 5.9, this function is marked as non-const.

setExtraFileSelectors(extraFileSelectors)¶

Parameters:: extraFileSelectors – list of strings

Sets the extraFileSelectors to be passed to the internal QQmlFileSelector used for resolving URLs to local files. The extraFileSelectors are applied when the first QML file is loaded. Setting them afterwards has no effect.

See also

QQmlFileSelector setExtraSelectors

setInitialProperties(initialProperties)¶

Parameters:: initialProperties – Dictionary with keys of type .QString and values of type QVariant.

Sets the initialProperties with which the QML component gets initialized after it gets loaded.

QQmlApplicationEngine engine;

EventDatabase eventDatabase;
EventMonitor eventMonitor;

engine.setInitialProperties({
    { "eventDatabase", QVariant::fromValue(&eventDatabase) },
    { "eventMonitor", QVariant::fromValue(&eventMonitor) }
});