Android platform support and APIs

Compilation for Android

The compiler generates an APK file as the output when the android module is imported by the compilation target. The path to the generated file can be specified using the -o and --dir options.

Host system configuration

To compile Android apps from a 64 bits GNU/Linux host you can reuse an existing Android Studio installation or make a clean install with command line tools only.

Note that this guide supports only 64 bits GNU/Linux hosts with support for a Java 8 JDK, it may be possible to support other platforms with some tweaks.

1. Install the required SDK packages using one of these two methods:

   a. Using Android Studio, open Tools > Android > SDK Manager, in the SDK Tools tab,

   install "Android SDK Build-Tools", CMake and NDK.
   

   b. From the command line, run this script for a quick setup without Android Studio.

   You will probably need to tweak it to you system or update the download URL
   to the latest SDK tools from https://developer.android.com/studio/index.html#command-tools
   

   # Fetch and extract SDK tools
   mkdir -p ~/Android/Sdk
   cd ~/Android/Sdk
   wget https://dl.google.com/android/repository/sdk-tools-linux-3859397.zip
   unzip sdk-tools-linux-3859397.zip
   
   # Update tools
   tools/bin/sdkmanager --update
   
   # Accept the licenses
   tools/bin/sdkmanager --licenses
   
   # Install the basic build tools
   tools/bin/sdkmanager "build-tools;27.0.0" ndk-bundle
   

2. Set the environment variable ANDROID_HOME to the SDK installation directory, usually ~/Android/Sdk/. Use the following command to setup the variable for bash.

   echo "export ANDROID_HOME=~/Android/Sdk/" >> ~/.bashrc
   

3. Install Java 8 JDK, on Debian/Ubuntu systems you can use the following command:

   sudo apt install openjdk-8-jdk
   

Configure the Android application

The app.nit framework and this project offers some services to customize the generated Android application.

Annotations

• All app.nit annotations are applied to Android projects: app_name, app_namespace and app_version.

  See: ../app/README.md

• Custom information can be added to the Android manifest file using the annotations android_manifest, android_manifest_application and android_manifest_activity.

  Example usage to specify an extra permission:

  android_manifest """<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>"""
  

• The API version target can be specified with android_api_min, android_api_max and android_api_target. These take a single integer as argument. They are applied in the Android manifest as minSdkVesion, targetSdkVersion and maxSdkVersion.

  See http://developer.android.com/guide/topics/manifest/uses-sdk-element.html

• The annotation android_activity defines a Java class used as an entry point to your application. As of now, this annotation should only be used by low-level implementations of Nit on Android. Its usefulness will be extended in the future to customize user applications.

Android implementation

There is two core implementation for Nit apps on Android. android::nit_activity is used by apps with standard windows and native UI controls. android::game is used by, well, games and the game frameworks mnit and gamnit.

Clients don't have to select the core implementation, it is imported by other relevant modules. For example, a module importing app::ui and android will trigger the importation of android::nit_activity.

Lock app orientation

Importing android::landscape or android::portrait locks the generated application in the specified orientation. This can be useful for games and other multimedia applications.

Resources and application icon

Resources specific to the Android platform should be placed in an android/ folder at the root of the project. The folder should adopt the structure of a normal Android project, e.g., a custom XML resource file can be placed at android/res/values/color.xml to be compiled with the Android application.

The application icon should also be placed in the android/ folder. Place the classic bitmap version at android/res/mipmap-hdpi/ic_launcher.png (and others), and the adaptive version at android/res/mipmap-anydpi-v26/ic_launcher.xml. The Nit compiler detects these files and uses them as the application icon.

Additional android/ folders may be placed next to more specific Nit modules to change the Android resources for application variants. The more specific resources will have priority over the project level android/ files.

Compilation modes

There are two compilation modes for the Android platform, debug and release. Theses modes are also applied to the generated Android projects. The compilation mode is specified as an argument to nitc, only --release can be specified as debug is the default behavior.

Debug mode

Debug mode enables compiling to an APK file without handling signing keys and their password. The APK file can be installed to a local device with USB debugging enabled, but it cannot be published on the Play Store.

By default, nitc will compile Android applications in debug mode.

Release mode

Building in release mode will use your private key to sign the APK file, it can then be published on the Play Store.

1. Have a keystore with a valid key to sign your APK file.

   To create a new keystore, avoid using the default values of jarsigner as they change between versions of the Java SDK. You should instead use a command similar to the following, replacing KEYSTORE_PATH and KEY_ALIAS with the desired values.

   keytool -genkey -keystore KEYSTORE_PATH -alias KEY_ALIAS -sigalg MD5withRSA -keyalg RSA -keysize 1024 -validity 10000
   

2. Set the environment variables used by nitc: KEYSTORE, KEY_ALIAS and optionally TSA_SERVER. These settings can be set in a startup script such as ~/.bashrc or in a local Makefile.

   You can use the following commands by replacing the right-hand values to your own configuration.

   export KEYSTORE=keystore_path
   export KEY_ALIAS=key_alias
   export TSA_SERVER=timestamp_authority_server_url # Optional
   

3. Call nitc with the --release options. You will be prompted for the

   required passwords as needed by jarsigner.