[Android Things] Using a local version of Mraa to build Upm for Android Things

This wiki is an step-by-step guide on how to modify the default Docker image that builds Upm for Android Things, in order to use a local version of Mraa.

Initial Setup

Note: for the example, this wiki will use some specific folders, you should change them to your proper folders to make this work.

The Docker image that builds Android Things has an Mraa repository in it. This Mraa repository is also built for Android Things, so Upm can just use that to build. But if for any reason you need to use a local version of Mraa to build Upm Android Things Packages, you can do:

1. Clone the Mraa repository in i.e /home/user/mraa

$ cd /home/user
$ git clone https://github.com/intel-iot-devkit/mraa.git
$ cd mraa

2. Build Mraa for Android Things

$ docker-compose run android

# After some time, mraa will be installed in /home/user/mraa/install
$ ls install/
bin  include  lib  share

3. Clone the Upm repository in /home/user/upm

$ cd /home/user
$ git clone https://github.com/intel-iot-devkit/upm.git
$ cd upm

4. Change docker-compose.yaml, mount your local Mraa repository into the container:

  android:
    extends: java
    image: dnoliver/upm-android
    environment:
      - BUILDTESTS=OFF
    command: bash -c "./scripts/build-android.sh"
    volumes:
      # Using a global path
      - /home/user/mraa:/opt/mraa
      # You can also use a relative path
      # - ./../mraa:/opt/mraa

5. Modify /home/user/mraa/install/lib/pkgconfig files to point to mraa install folder inside the container. This is mandatory to allow cmake to find mraa files:

# Go to Mraa repository
$ cd /home/user/mraa

# Modify install/lib/pkgconfig/mraa.pc
$ sudo sed -i 's$/usr/src/app/install$/opt/mraa/install$' install/lib/pkgconfig/mraa.pc 

# Modify install/lib/pkgconfig/mraajava.pc
$ sudo sed -i 's$/usr/src/app/install$/opt/mraa/install$' install/lib/pkgconfig/mraajava.pc

# In both files, prefix property should be /opt/mraa/install
# prefix=/opt/mraa/install

6. Build Upm for Android Things

$ cd /home/user/upm
$ docker-compose run android

Updating Mraa code for upm builds

After you did the initial setup, you can keep building new versions of libmraa, and use it to re-build upm modules for Android Things.

This is a short example on how to achieve this:

1. Modify a source file in Mraa repository

# Go to Mraa repository folder
$ cd /home/user/mraa

# Modify a file
$ nano CmakeLists.txt

2. Execute Step 2, 5 and 6 from the Initial Setup