source: trunk/doc/src/declarative/qmlruntime.qdoc

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/*!
\page qmlruntime.html
\title Qt Declarative UI Runtime

QML 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 QDeclarativeView 
or a QDeclarativeEngine, as described below. In addition, the Declarative UI 
package includes the \QQV tool, which loads \c .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.



\section1 Deploying QML-based applications

To 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
QDeclarativeEngine by either:

\list
\o Loading the QML file through a QDeclarativeView instance, or
\o Creating a QDeclarativeEngine instance and loading QML files with QDeclarativeComponent
\endlist


\section2 Deploying with QDeclarativeView

QDeclarativeView is a QWidget-based class that is able to load QML files.
For example, if there is a QML file, \c application.qml, like this:

\qml
    import QtQuick 1.0
    
    Rectangle { width: 100; height: 100; color: "red" }
\endqml

It can be loaded in a Qt application's \c main.cpp file like this:
 
\code
    #include <QApplication>
    #include <QDeclarativeView>

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

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

        return app.exec();
    }
\endcode
       
This creates a QWidget-based view that displays the contents of 
\c application.qml.
 
The application's \c .pro \l{qmake Project Files}{project file} must specify
the \c declarative module for the \c QT variable. For example:

\code
    TEMPLATE += app
    QT += gui declarative
    SOURCES += main.cpp
\endcode


\section2 Creating a QDeclarativeEngine directly
     
If \c application.qml does not have any graphical components, or if it is 
preferred to avoid QDeclarativeView for other reasons, the QDeclarativeEngine
can be constructed directly instead. In this case, \c application.qml is
loaded as a QDeclarativeComponent instance rather than placed into a view:

\code
    #include <QApplication>
    #include <QDeclarativeEngine>    
    #include <QDeclarativeContext>
    #include <QDeclarativeComponent>

    int main(int argc, char *argv[])
    {
        QApplication app(argc, argv);
    
        QDeclarativeEngine engine;
        QDeclarativeContext *objectContext = new QDeclarativeContext(engine.rootContext());
    
        QDeclarativeComponent component(&engine, "application.qml");
        QObject *object = component.create(objectContext);
         
        // ... delete object and objectContext when necessary
    
        return app.exec();
    }
\endcode

See \l {Using QML in C++ Applications} for more information about using 
QDeclarativeEngine, QDeclarativeContext and QDeclarativeComponent, as well 
as details on including QML files through \l{The Qt Resource System}{Qt's Resource system}.



\section1 Developing and prototyping with QML Viewer

The Declarative UI package includes a QML runtime tool, the \QQV, 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. 

See the \l{QML Viewer} documentation for more details.

*/