Porting to Android

Most Qt applications should be portable to Android with ease, unless they depend on a specific hardware or software feature not supported by Android. If your application is not using any such feature, deployment is the only step that might demands some changes to your application.

Like most UI applications, Qt applications also depend on resources such as images, icons, translation files, and so on. These resources must be made available on the device as they are required for the application to function correctly.

The most convenient option is to bundle the resources into a qrc file, which gets built into the application binary. This approach reduces the porting effort considerably and provides faster access to the resources. It is also a cross-platform approach, which makes porting to other platforms easier.

By default, all Qt applications can access the contents of a qrc file using the ":/" prefix or the URL scheme prefix, "qrc:". To know more about qrc files and how they are handled, see the Qt Resource System.

The other approach is to deploy the resources into the package's assets directory. It is the best option if you want to achieve better interoperability with the Android APIs. You can access all resources in the directory using the "assets:" prefix. Unlike qrc, this approach is Android specific, not a cross-platform solution.

To use the "assets:" approach, for example, add the following lines into the .pro file:

android {
    assets.files = images/happy.png
    assets.path = /assets/images/
    INSTALLS += assets
}

Then you can access that image asset from C++ as follows:

QImage image("assets:/images/happy.png");

The following step-by-step instructions guide you to port an existing Qt Quick application to Android using the qrc approach:

1. Open your project in Qt Creator and select an Android kit. For more information, see Configuring Projects in Qt Creator.
2. Identify all the resources used by your application and add them to one or more qrc files. Qt Creator updates your qmake project file with the "RESOURCES" variable listing the qrc files you added.
3. To load or refer to the resources in the qrc file from your C++ code, use the "qrc:" scheme followed by the absolute URL. For example, to load the main.qml file from resources.qrc, you can use the following C++ code:

   QQuickView viewer;
   viewer.setSource(QUrl("qrc:/qml/main.qml"));
   viewer.show();

   Note: QML documents can refer to the contents in qrc files using the relative path to the document. Such references do not require the "qrc:" or ":/" prefix.

4. Deploy your application to a device or AVD. For more information, see Qt Creator: Deploying Applications to Android Devices.