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KDE software on Android

Android is currently the mobile platform regarding market share and number of provided applications. Hence, it is a platform very well suited to increase the availability and usage of applications by the KDE community. In the following, we give an overview of the technical steps required to setup a build system for cross-compiling a Qt5/KF5 based Android application, the necessary steps to deploy it, and a reference list of the porting steps by different applications/people.

Tutorial for Building Applications 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 according tools for building Java applications.

Prerequisites / Setup of Cross-Compiling Build System

At first we prepare your system with all necessary packages to build your application for Android. For this tutorial we assume that everything is done in the folder /opt/android/ (you can adapt the tutorial accordingly when using another folder).

Some 32 bit system libraries are required for the host system (because some tools are 32 bit):
- libgcc, zlib, libc
installing on Debian based system:
- dpkg --add-architecture i386
- apt-get install zlib1g:i386 libgcc1:i386 libc6:i386
Extra-CMake-Modules
- we require at least version >= 5.15 due to https://git.reviewboard.kde.org/r/125183
- you can also use a smaller version >= 1.7.0 if applying this change directly to your cmake files
Android SDK
- Download: http://developer.android.com/sdk/index.html to /opt/android/
- Unpack, run "tools/android update sdk" and select the following packages:
  - Android SDK Tools (24.3.4)
  - Android SDK Platform-tools (23.0.1)
  - Android SDK Build-tools (22.0.1)
  - Android 5.1.1 (API 22): SDK Platform (only "SDK Platform" needed, i.e. no docs, samples or sources)
- result: now the SDK should be installed in /opt/android/android-sdk-linux
Android NDK
- Download: https://developer.android.com/ndk/index.html to /opt/android/
- unpack the package (see the instructions on the download page)
- result: now the NDK should be installed in /opt/android/android-ndk-r10e
Qt with support for Android devices
- Download the Qt 5.5.0 for Android: https://www.qt.io/download-open-source/#section-2 (32-bit or 64-bit as it fits your host system; usually 64-bit)
- Variant 1: Offline Installers ("Skip" can be used without problem when asked to register an account)
- Variant 2: Online installer ("Skip" can be used without problem when asked to register an account)
- install the following components to /opt/android/Qt5.5.0:
  - Android armv7
  - Qt Creator 3.4.2 (cannot be disabled, some of its tools are used from other parts)
  - Recommended components:
    - Qt Quick Controls
    - Qt Location
    - Qt Script
    - Optional components (there might be KDE software using it):
    - Qt WebEngine
    - Qt Canvas 3D
    - Qt3D
    - Qt Quick 1
Install the following software packages on your host system from your package manager (if not yet installed):
- CMake: >= 2.8.6
- Java Development Kit 7 (openjdk-7-jdk)
- Ant

Setup Build Environment

The build environment is the name for the shell in that the application is build. The shell is prepared by exporting a series of environment variables that then are picked up by the build scripts.

export ADIR=/opt/android
export ANDROID_NDK=$ADIR/android-ndk-r10e
# note the _ROOT postfix here, different pattern
export ANDROID_SDK_ROOT=$ADIR/android-sdk-linux
export Qt5_android=$ADIR/Qt5.5.0/5.5/android_armv7/
export ANDROID_API_VERSION=android-22
export PATH=$ADIR/android-sdk-linux/platform-tools/:$PATH
# adapt the following path to your ant installation
export ANT=/usr/bin/ant
# adapt the following path to your openjdk location, eg:
#  openSUSE: /usr/lib64/jvm/java (needs default version being properly set, see notes below)
#  Debian: /usr/lib/jvm/java-7-openjdk-amd64
export JAVA_HOME=/usr/lib/jvm/java-7-openjdk/

Some notes:

/opt/android should be replaced with the custom build folder selected by you
Java platform 7 is needed (both JRE and JDK). One can select the Java platform versions e.g. with update-alternatives --config java and update-alternatives --config javac
Use jrunscript -e 'java.lang.System.out.println(java.lang.System.getProperty("java.home"));' to find the JAVA_HOME

Building

Example: Building Marble

cd /opt/android
git clone kde:marble
mkdir marble/build
cd marble/build
cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_TOOLCHAIN_FILE=/PATH/TO/ECM/toolchain/Android.cmake -DCMAKE_PREFIX_PATH=$Qt5_android -DQT_NO_WEBKIT=TRUE -DQT_NO_PRINTER=TRUE  -DQT_NO_DBUS=TRUE -DCMAKE_INSTALL_PREFIX=../export  ..
make install/strip

Note:

/PATH/TO/ECM/toolchain/Android.cmake must be replaced with the actual path to toolchain/Android.cmake
make install/strip strips build symbols from the binaries and reduces sizes considerably

Building with KDESRC-BUILD

For building the below mentioned frameworks on Android, you can use the following kdesrc-buildrc config file:

cd /opt/android
git clone git://anongit.kde.org/scratch/cordlandwehr/kdesrc-conf-android.git
mkdir -p extragear/kdesrc-build
git clone kde:kdesrc-build extragear/kdesrc-build
ln -s extragear/kdesrc-build/kdesrc-build kdesrc-build
ln -s kdesrc-conf-android/kdesrc-buildrc kdesrc-buildrc
./kdesrc-build extra-cmake-modules frameworks-android

Packaging and Deployment of APKs

Note

See ECM Toolchain documentation, to be added here as example

Status of KDE Frameworks 5

The following frameworks can currently be used for Qt5/KF5 based applications. They are not (yet?) provided as precompiled libraries but can easily be compiled via kdesrc-build.

Built Successfully

kconfig (note: unit tests must be disabled)
kcompletion
kitemmodels
kitemviews
kcodecs
karchive
kguiaddons
kwidgetsaddons
attica
kdnssd
kapidox
kimageformats
kplotting

Current Blockers

The following frameworks cannot yet be built and block building of further Tier 1 frameworks:

kcoreaddons: unix specific backend not compatible with Android's libc
ki18n: dependency on libintl, which is not available on Android
- usage of libintl-light currently under investigation

"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. Well, almost the same currently with ECM < 5.15.0, as some issues need work-arounds still to be done. See the section in the if in the toplevel CMakeLists.txt:

project(hellokandroid)

# AndroidToolchain needs it
cmake_minimum_required(VERSION 3.1.0)

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

if (CMAKE_SYSTEM_NAME STREQUAL Android)
    find_package(ECM)
    # TODO: possibly should be setup by toolchain one day
    set(QT_QMAKE_EXECUTABLE "$ENV{Qt5_android}/bin/qmake")
    # workaround until this fix is in released ECM
    if(ECM_VERSION VERSION_LESS "5.15.0")
        add_definitions(-DANDROID)
    endif()
endif()

add_subdirectory(src)

When creating the APK package, as with normal Android 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="9" 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 with workarounds for current issues in ECM < 5.15.0, by git clone git://anongit.kde.org/scratch/kossebau/hellokandroid.git

Further References

References:

Extra-CMake-Modules Toolchain: API documentation

Application specific build instructions:

Marble: build instructions

Blog posts about building for Android (careful: instructions may be outdated)

2015-09 - Dennis Nienhüser: Announcing Marble Maps for Android Open Beta
2015-04 - Péterffy Gábor: Marble is coming to Android
2015-01 - GCompris Devels: GCompris is now released on Android
2014-06 - Alex Pol: KDE Software on Android

Current TODOS

add ported applications to kdesrc file -> CoLa
provide preconfigured docker image for the whole setup -> CoLa
provide small example project to test building and deploying: -> Friedrich (?)