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Qt Declarative UI RuntimeQML documents are loaded and executed by the QML runtime. This includes the Declarative UI engine along with the built-in QML elements and plugin modules, and it also provides access to third-party QML elements and modules. Applications that use QML need to invoke the QML runtime in order to execute QML documents. This can be done by creating a QQuickView or a QQmlEngine, as described below. In addition, the Declarative UI package includes the qmlscene tool, which loads .qml files. This tool is useful for developing and testing QML code without the need to write a C++ application to load the QML runtime. Deploying QML-based applicationsTo deploy an application that uses QML, the QML runtime must be invoked by the application. This is done by writing a Qt C++ application that loads the QQmlEngine by either:
Deploying with QQuickViewQQuickView is a QWidget-based class that is able to load QML files. For example, if there is a QML file, application.qml, like this: import QtQuick 2.0 Rectangle { width: 100; height: 100; color: "red" } It can be loaded in a Qt application's main.cpp file like this: #include <QApplication> #include <QQuickView> int main(int argc, char *argv[]) { QApplication app(argc, argv); QQuickView view; view.setSource(QUrl::fromLocalFile("application.qml")); view.show(); return app.exec(); } This creates a QWidget-based view that displays the contents of application.qml. The application's .pro project file must specify the declarative module for the QT variable. For example: TEMPLATE += app QT += gui declarative SOURCES += main.cpp Creating a QQmlEngine directlyIf application.qml does not have any graphical components, or if it is preferred to avoid QQuickView for other reasons, the QQmlEngine can be constructed directly instead. In this case, application.qml is loaded as a QQmlComponent instance rather than placed into a view: #include <QApplication> #include <QQmlEngine> #include <QQmlContext> #include <QQmlComponent> int main(int argc, char *argv[]) { QApplication app(argc, argv); QQmlEngine engine; QQmlContext *objectContext = new QQmlContext(engine.rootContext()); QQmlComponent component(&engine, "application.qml"); QObject *object = component.create(objectContext); // ... delete object and objectContext when necessary return app.exec(); } See Using QML Bindings in C++ Applications for more information about using QQmlEngine, QQmlContext and QQmlComponent, as well as details on including QML files through Qt's Resource system. Developing and Prototyping with QML ViewerThe Declarative UI package includes a QML runtime tool, qmlscene, which loads and displays QML documents. This is useful during the application development phase for prototyping QML-based applications without writing your own C++ applications to invoke the QML runtime. |
