Tutorial for CMake/ECM-based app on Android

For building Qt applications on Android, some extra steps are required in comparison to building directly on Linux. The following instruction expects that KF5/Qt5 based applications can already be built and all necessary tools are installed (gcc, cmake, git,...). The main idea for the setup is that we use precompiled Qt libraries (named NDK and SDK), which are built for the ARM-based Android platform. All building then is done by using these libraries. Still the build-process itself will use the tools from your Linux system (in the following called "host system"; while the Android device is called "target system"). The additional tools mostly are the Java Development Kit and other tools for building Java applications.

1. Setup Build Environment

Follow the steps in

Cross-Building Environment for Qt on Android

to setup a cross-building environment. Then continue with the next step.

2. Build "Hello KWorld" Example

Simple example how to create Qt-based apps for Android using CMake and ECM.

Take a simple "Hello world" example app using QtQuick2 with a resource file:

#include <QGuiApplication>
#include <QQmlApplicationEngine>

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

    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

    return app.exec();
}

It's CMakeLists.txt files would be the same as for a normal/desktop application. All special setup for the target system is done via the toolchain file, which is passed via the cmake parameter on the commandline:

cmake_minimum_required(VERSION 3.1.0)

project(hellokandroid)

set(QT_REQUIRED_VERSION 5.3.0)
find_package(Qt5Qml)
find_package(Qt5Quick)

add_subdirectory(src)

When creating the APK package, as with normal Android apps a manifest file is needed which describes what the package contains and needs, named AndroidManifest.xml. For a simple application that should appear on the app grid this would be the minimum needed with an Qt-based app:

<?xml version="1.0"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" android:versionName="0.0.3" package="org.kde.hellokandroid" android:installLocation="auto" android:versionCode="7">
        <application android:name="org.qtproject.qt5.android.bindings.QtApplication"
                     android:label="Hello KWorld"
                     android:icon="@drawable/kde">
                <activity android:name="org.qtproject.qt5.android.bindings.QtActivity"
                          android:label="Hello KWorld"
                          android:screenOrientation="unspecified"
                          android:configChanges="orientation|uiMode|screenLayout|screenSize|smallestScreenSize|locale|fontScale|keyboard|keyboardHidden|navigation">
                        <intent-filter>
                                <action android:name="android.intent.action.MAIN"/>
                                <category android:name="android.intent.category.LAUNCHER"/>
                        </intent-filter>
                        <meta-data android:name="android.app.lib_name" android:value="-- %%INSERT_APP_LIB_NAME%% --"/>
                        <meta-data android:name="android.app.qt_sources_resource_id" android:resource="@array/qt_sources"/>
                        <meta-data android:name="android.app.repository" android:value="default"/>
                        <meta-data android:name="android.app.qt_libs_resource_id" android:resource="@array/qt_libs"/>
                        <meta-data android:name="android.app.bundled_libs_resource_id" android:resource="@array/bundled_libs"/>
                        <!-- Deploy Qt libs as part of package -->
                        <meta-data android:name="android.app.bundle_local_qt_libs" android:value="-- %%BUNDLE_LOCAL_QT_LIBS%% --"/>
                        <meta-data android:name="android.app.bundled_in_lib_resource_id" android:resource="@array/bundled_in_lib"/>
                        <meta-data android:name="android.app.bundled_in_assets_resource_id" android:resource="@array/bundled_in_assets"/>
                        <!-- Run with local libs -->
                        <meta-data android:name="android.app.use_local_qt_libs" android:value="-- %%USE_LOCAL_QT_LIBS%% --"/>
                        <meta-data android:name="android.app.libs_prefix" android:value="/data/local/tmp/qt/"/>
                        <meta-data android:name="android.app.load_local_libs" android:value="-- %%INSERT_LOCAL_LIBS%% --"/>
                        <meta-data android:name="android.app.load_local_jars" android:value="-- %%INSERT_LOCAL_JARS%% --"/>
                        <meta-data android:name="android.app.static_init_classes" android:value="-- %%INSERT_INIT_CLASSES%% --"/>
                        <!--  Messages maps -->
                        <meta-data android:name="android.app.ministro_not_found_msg" android:value="@string/ministro_not_found_msg"/>
                        <meta-data android:name="android.app.ministro_needed_msg" android:value="@string/ministro_needed_msg"/>
                        <meta-data android:name="android.app.fatal_error_msg" android:value="@string/fatal_error_msg"/>
                </activity>
        </application>
        <supports-screens android:anyDensity="true" android:normalScreens="true" android:smallScreens="true" android:largeScreens="true"/>
        <uses-sdk android:minSdkVersion="16" android:targetSdkVersion="19"/>
</manifest>

"android:label" would be the display name of your app. For the icon to be used for your app, "android:icon" defines it. The value "@drawable/kde" refers to an icon in PNG format, that is to be found in a subdir "res/drawable" relative to the manifest file, in our case "res/drawable/kde.png".

Get the complete example code, incl. step-by-step build instructions, by git clone git://anongit.kde.org/scratch/kossebau/hellokandroid.git