Qt: Resource Management

Overview

In Qt, the resource system makes the use of runtime files platform-independent. It does this in at least two ways:

1) Avoiding the use of user-specific path names (e.g. /home/robby/Documents)

2) Avoiding filesystem-specific path conventions (e.g. Windows C:\Documents\ vs Linux /usr/bin/ls)

Resources are local files that are brought in at runtime. Examples are qml files, media files, and meshes among other things. C++ source and header files are not considered resources as they are compiled.

How to use

The project’s .pro file points the build system at a qrc (Qt resource collection) file with something like this:

# within the .pro file, point the build system at the
# .qrc file via the RESOURCES variable
RESOURCES += resources.qrc

A qrc file is XML. It specifies main.qml as well as other files like media. A qrc file might look something like this:

<RCC>
    <qresource prefix="/">
        <file>main.qml</file>
        <file>images/denmark.jpg</file>
        <file>images/finland.jpg</file>
        <file>images/iceland.jpg</file>
        <file>images/norway.jpg</file>
        <file>images/sweden.jpg</file>
    </qresource>
</RCC>

This will then make resources available elsewhere in the code. For example main.cpp might look like this:

#include <QGuiApplication>
#include <QQuickView>

int main( int argc, char** argv ) {
    QGuiApplication app( argc, argv );
    QQuickView view;

		// Here we can access main.qml with this syntax:
    view.setSource(QUrl("qrc:main.qml"));
    view.show();

    return app.exec();
}

And elsewhere (in another source file):

MyModel::MyModel(QObject *parent) :
    QAbstractListModel(parent)
{
// and here we can access them too
    m_data
        << Data("Denmark", "qrc:images/denmark.jpg", 5.6)
        << Data("Sweden", "qrc:images/sweden.jpg", 9.6)
        << Data("Iceland", "qrc:images/iceland.jpg", 0.3)
        << Data("Norway", "qrc:images/norway.jpg", 5.1)
        << Data("Finland", "qrc:images/finland.jpg", 5.4);

    QTimer *growthTimer = new QTimer(this);
    connect(growthTimer, &QTimer::timeout, this, &MyModel::growPopulation);
    growthTimer->start(2000);
}

Summary

The Qt resource systems allows filesystem-independent installations of projects. The steps involved are

1) tell the build system about the qrc file in the .pro file

2) specify resources in the qrc file and

3) access the resources in the code via the syntax “qrc:<resource>”