- Qt 6.12
- Qt Qml
- Initializing the QML Runtime
- Qt 6.12.0 Reference Documentation

Making Applications Scriptable with JavaScript ◦ Prototyping, Debugging and Profiling QML Applications

# Initializing the QML Runtime

QML documents are loaded and run by the QML runtime. The QML runtime also provides access to other Qt or third-party QML modules and types.

In addition, the Qt Framework provides the `qml` tool, which loads `.qml` files. This tool is useful for developing and testing QML code without having to write a C++ application to load the QML runtime.

To run an application that uses QML, your application must invoke the QML runtime. To invoke the QML runtime:

- Create a Qt C++ application.

  The application should load the QQmlEngine in one of the following ways:

  - Loading the QML file through a QQuickView instance.
  - Creating a QQmlEngine instance and loading QML files with QQmlComponent.
- Create a Qt Bridges application.

  For details, see Qt Bridges documentation:

  - Qt Bridges for C#
  - Qt Bridges for Rust
- Use the `qml` tool to load and run QML files directly.

  This tool is useful for developing and testing QML code without having to write an application to load the QML runtime. For details, see Prototyping with the QML Runtime Tool.

## Initializing the QML Runtime in C++ Applications

### Initializing with QQuickView

QQuickView is a QWindow-based class that can load QML files. For example, if there is a QML file, `application.qml`, it will look like this:

     import QtQuick

     Rectangle { width: 100; height: 100; color: "red" }

It can be loaded in a Qt application's `main.cpp` file like this:

     #include <QGuiApplication>
     #include <QQuickView>

     int main(int argc, char *argv[])
     {
         QGuiApplication app(argc, argv);

         QQuickView view;
         view.setSource(QUrl::fromLocalFile("application.qml"));
         view.show();

         return app.exec();
     }

This creates a QWindow-based view that displays the contents of `application.qml`.

#### Build files

##### Using CMake

Use the `find_package()` command to locate the needed module component in the `Qt6` package:

     find_package(Qt6 REQUIRED COMPONENTS Quick)
     target_link_libraries(mytarget PRIVATE Qt6::Quick)

For more details, see the Build with CMake overview.

##### Using qmake

To configure the module for building with qmake, add the module as a value of the `QT` variable in the project's .pro file:

     QT += quick

For more information, see Creating Project Files.

### Creating a QQmlEngine directly

If `application.qml` doesn't have any graphical components, or if it's 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 <QGuiApplication>
     #include <QQmlEngine>
     #include <QQmlContext>
     #include <QQmlComponent>

     int main(int argc, char *argv[])
     {
         QGuiApplication 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();
     }

If you're not using any graphical items from Qt Quick, you can replace QGuiApplication with a QCoreApplication in the code above. This way, you can use QML as a language without any dependencies to the Qt GUI module.

Making Applications Scriptable with JavaScript ◦ Prototyping, Debugging and Profiling QML Applications