Introduction to the Android SDK

Android SDK

• Tools for Android application development
• Downloadable from the Android developer site
  • It can be downloaded standalone (to be used with the CLI)
  • If we use Android Studio, on the first launch a wizard proposes to download the SDK
• Main components of the Android SDK :
  • tools/: tools of the SDK
    • bin/
      • sdkmanager: package manager of the SDK
        • To download tools for new versions of the API, related documentations
        • To update existing components of the SDK (bug and security fixes, improvements...)
      • avdmanager: tool to managed virtual machines (Android Virtual Devices): creation, modification, destruction
      • lint: tool to statically analyze the source code (to find problems, bugs...)
        • Embedded in Android Studio
      • screenshot2: to capture screenshots on the Android device
      • uiautomatorviewer: tool to inspect the UI (to get the tree of components)
      • apkanalyzer: tool to extract data from an APK package (to fetch the manifest, the DEX bytecode, the list of resources...)
        • Embedded in Android Studio (menu Build > Analyze APK)
      • jobb: tool to create OBB extension packages (to gather additional resources for an application)
    • emulator: x86 and ARM emulator to start Android Virtual Devices
    • monitor: live monitoring tool for Android applications
      • supplies the used memory, the network trafic, the CPU load, can be used to inject fake calls and SMS...
      • Embedded in Android Studio
  • mkdsdcard: tool to create virtual SD cards for Android Virtual Devices
  • build-tools/: tools to compile projects (one directori for each API version)
    • Header files
    • Libraries
    • Programs used for the compilation chain : aapt, aidl, zipalign, apksigner...
  • platform-tools: tools to communicate with an Android device
    • adb (Android Debug Bridge): program to communicate between the dev computer and the Android device (to execute commands, fetch logs with logcat...)
    • fastboot : program to flash Android devices (to change the booloader, the recovery partition, the modem firmware...)
  • system-images/: system images to create virtual devices (for several API levels and architectures)
  • platforms/ : resources for each API version
    • android.jar : file with all the signatures of classes amd methods of the Android API
  • docs/: documentation for the API (Javadoc)
    • samples/: samples of code
  • sources/: sources for each API level

☞ It is useful to add tools and platform-tools in the PATH environment variable

Android NDK

• Native Development Kit: to develop C/C++ libraries for Android applications
• Useful for:
  • new code tuning finely the memory (without using a garbage collector) and/or making intensive computations
  • to port C/C++ libraries to Android
• Access to the NDK from the managed code (Java, Kotlin...) using JNI calls (Java Native Interface)
• Rust can also be used with the NDK

Integrated Development Environment (IDE)

• Android Developer Tools (Eclipse)
  • Project built with an Ant Script
  • Obsolete
• Android Studio (IntelliJ IDEA, Jetbrains)
  • Project built with a Gradle script
  • First choice for Android development (official support by Google)
• NBAndroid (NetBeans)
• Xamarin (Microsoft Visual Studio)
  • Only available for Windows
  • Support for C#

SDK Manager

• Download (Windows, Linux, MacOS versions) : http://developer.android.com/sdk/
• Command: android sdk

Creating a virtual device

• One can use the graphical interface from Android Studio (Tools > AVD Manager)
• One can launch the standalone GUI: android avd
• Or use the CLI:
  • New SD card with a vfat FS: mksdcard -l carteSD 1024M carteSD.img
  • New virtual device: android create avd -c carteSD.img -n myAVD --snapshot --target android-17
  • Starting the virtual device: emulator @myAVD
  • Useful options: -sdcard <file>, -memory <sizeInMBs>, -shell, -logcat <tags>, -tcpdump <file>
  • For further information

Communication with ADB

Principles and startup

• ADB = Android Debug Bridge
• Components of the ADB system:
  • A client that runs on the development machine; it is used to send commands to the Android device
  • A server running on the development machine: it is contacted by the client; it is a relay between the client and the Android device
  • A daemon (adbd) running on the Android device that receives commands from the server and execute them
• How to activate adb communication with an Android device ?
  • Activate the developer mode by pressing several times on Build number from the About section of the settings app
  • Activate USB debugging in the new Development menu that has appeared in the settings app
  • Authorize the server from the computer used for development to contact adbd on the device (the computer is authentified with a cryptographic key)

☞ Some additional configuration may be required according to your OS. For example with Linux, if we use a physical Android device using an USB connection, this device must be registered using a udev rule to allow a normal user to access it.

Some useful commands

• adb push <source> <dest>: to copy a file from the local computer to the device
• adb pull <source> <dest>: to retrieve a file from the device to the local computer
• adb logcat <tags>: display the logs from logcat (tags can be used to filter the logs)
• adb shell: open an interactive shell on the Android device
• adb install <file>: install an application (APK package) on the Android device
• adb uninstall <package>: uninstall an application
• adb backup -f <file>: backup the user data
• adb restore <file>: restore the user data
• adb forward tcp:<local> tcp:<remote>: allow to access the port <local> of the Android device from the development computer using the port <remote> (thus we can run a server on the Android device and contact it from the computer)
• adb reverse tcp:<local> tcp:<remote>: allow to access the port <remote> of the developement computer from the Android device using the port <local> (thus a server can be run on the computer and the Android device can access it)
• Sous Linux des règles udev pour l'appareil peuvent être nécessaires (pour utiliser ADB sans être root), sous Windows l'installation de pilotes peut être requise

A glimpse of the standard Android API

android.* packages

• util: utility classes to analyze text, for logging, managing sparse arrays, caches...
• os : access to the IPC, to the energy manager, the clock, the environment variables, the vibrator...
• graphics : to handle images
• text: to display texts
• database: to manage databases using SQLite3
• content, provider: to manage content access across several applications
• view: legacy API for the graphical components
• widget: some useful views for GUIs
• app: base interfaces for the applications définition des interfaces de base des applications
• provider: to access common ContentProviders (CallLog, Contacts, MediaStore...)
• telephony, bluetooth, net: low-level access to communication features
• webkit: to display HTML content
• location: for geolocation (GPS, WiFi or cellular triangulation)
• media: recording and playback of AV data
• opengl: API for OpenGL rendering
• ...

Base classes to develop Android applications

The components of an Android applications must be implemented in classes that inherited from ome of this base classes:

• Activity: screen to interact with the user
• Fragment: chunk of screen that can be reused (deprecated with Jetpack Compose)
• Service : a kind of daemon that does a task in the background without graphical feedback
  • Can be called using RPC methods (from the same or another application)
  • Can be used to execute tasks that are sent to it using an Intent (overriding the onStartCommand method)
• ContentProvider: to expose a database of the application to another applications (examples: contacts, agenda...)
  • Implementations of ContentProvider typically on the use of SQLite
• BroadcastReceiver: to react to events sent by the system or other applications (it is a kind of communication bus)