Programming using the Android NDK with Qt Creator

I recently had to implement libraries for the Android OS using the Android NDK, or implementing JNIbindings for others to leverage C++ libraries from the Java layer. I commonly did this using simple tools like kate or similar text editors. To be sincere, it was not a completely satisfying approach.

During one of my projects, I had to port a Qt application to Android, using the excellent necessitas SDK. This excellent SDK made it possible to implement for Android using C++, the NDK and Qt Creator as the preferred IDE. I started from here to think I could use Qt Creator to more generally program in C++/JNI to implement libraries for Android, with or without the Qt libraries. This is how I did it.

Download the necessary tools

• Download the Qt libraries (I won’t use the libraries, I only need the environment).
• Download Qt Creator.
• Download the Android NDK for your platform.

Add the Android platform specification

I took the platform specification used in the necessitas project and modified it a bit. Look for the directory containing the platform specifications (<qt_libs>/mkspecs), and place in there the platform specification file and the qmake configuration file. You’ll have to define at least the ANDROID_NDK_ROOT to the root of the NDK you downloaded.

Setup Qt Creator

In Qt Creator you can specify a new toolchain to use: go to the preferences, “Build & Run”, “Toolchains”, “Add” and choose “GCC”. Then, select the gcc compile from the Android NDK (I see it under <ndk_root>/toolchains/arm-linux-androideabi-4.4.3/prebuilt/darwin-x86/bin/arm-linux-androideabi-g++). You’ll have to create a new build configuration in the project properties: add a new specification with the default build specification and name it differently. Also, under “Build Steps”, add “-spec android-g++” to the additional arguments. This will tell Qt Creator to build according to the Android specifications we added before. Also, select the Android toolchain in the “General” section.

Additional setup

Consider that I also had to remove QMAKE_INCDIR_QT in some cases because it was adding /usr/include to the include paths, thus making the build fail. You may want to add that to the qmake.conf file.

Creating native executables for Android using qmake and Qt Creator

It is sometime useful to creato native executables for Android. You can use this technique to do it very simply. For instance, this is a test I created in a minute (you can use Qt Creator or the command line directly):

nano TestProject.pro


QT              -= core gui
TEMPLATE        = app
SOURCES         = main.cpp
QMAKE_INCDIR_QT =

Now write a simple “Hello Android!” application:

nano main.cpp


#include <stdio.h>


int main(int argc, char** argv)
{
   printf("Hello Android!n");
   return 0;
}

Now create the Makefile using qmake and the android platform specification:

qmake -spec android-g++
make

You’ll get a TestProject execuable compiled for arm platform using the Android bionic C libraries. You can try uploading to an Android emulator:

luca-macbook:test_project luca$ adb remount
remount succeeded
luca-macbook:test_project luca$ adb push TestProject /data
173 KB/s (34639 bytes in 0.195s)
luca-macbook:test_project luca$ adb shell
# cd /data
# ./TestProject
Hello Android!
# rm TestProject

I used this approach on both Mac OS X and Linux. Never tried on Windows.