Category: sl4a

SL4A – Utilities using Python Facades ”; Previous Next Email-based Applications Email based applications are one of the most common utilities available in a mobile device. One can use the sendEmail API call available through the SL4A Android facade. This function takes three parameters − to_address − a comma-separated list of recipients. title − represents the title of the email message. message − represents the message to be sent. import android,datetime,smtplib from email.mime.multipart import MIMEMultipart from email.mime.text import MIMEText droid = android.Android() serv = ’smtp.gmail.com’ port = 587 mailto = ’chris’ mailfrom = ’charley’ pass = ’pass@123’ msg = MIMEMultipart() msg[‘Subject’] = ’Tes Mail’ msg[‘To’] = mailto msg[‘From’] = mailfrom body = ’This is a test mail!!’ msg.attach(MIMEText(body,’plain’)) smtpCon = smtplib.SMTP(serv,port) smtpCon.starttls() smtpCon.login(mailfrom,pass) smtpSendmail(mailfrom,mailto,msg.as_string()) smtpCon.close() The python library that have used to build the email program is smtplib. In addition, we have used the email library. This library contains a number of helper functions allowing us to construct our message in the correct form. The mimetypes library helps with the encoding of our message. Wifi Scanner The following code lists all available Wi-Fi access spots − import android, time def main(): global droid droid = android.Android() while not droid.wifiStartScan().result: time.sleep(0.25) networks = {} while not networks: for ap in in droid.wifiGetScanResults().result: networks[ap[‘bssid’]] = ap.copy() droid.dialogCreateAlert(‘Access Points’) droid.dialogSetItems([‘%(ssid)s,%(level)s,%(capabilities)s’ % ap for ap in networks.values() ]) droid.dialogSetPositiveButtonText(‘OK’) dorid.dialogShow() if __name__=’__main__’: main() Call Logs The code for call logs is given below. import android droid = android.Android() mylog = droid.getConstants(“android.provider.Calllog$Calls”).result calls = droid.queryContent(mylog[“CONTENT_URI”],[“name”,”number”,”duration”]).result for c in calls: print c Print Page Previous Next Advertisements ”;

SL4A – Navigating the Android SDK ”; Previous Next A software development kit that enables developers to create applications for the Android platform. The Android SDK includes sample projects with source code, development tools, an emulator, and required libraries to build Android applications. This chapter discusses the Android SDK and ways to use it for developing the code targeted at SL4A. SDK Components The directory tree where you installed the Android SDK, contains a list of folders containing documentation, sample code and a number of tools. Navigating to the tools subdirectory reveals a number of executable files. Discussed below are some important components within the Android SDK. SDK Manager The Android SDK Manager separates the SDK tools, platforms, and other components into packages for easy access and management. The SDK can be configured to check for new or updated SDK packages and add-on tools. By default, Android Studio does not check for Android SDK updates. To enable automatic Android SDK checking − Step 1 − Choose File → Settings → Appearance & Behavior → System Settings → Updates. Step 2 − Check the Automatically check updates for Android SDK checkbox and select an update channel. Step 3 − Click OK or Apply to enable the update checking. The SDK Update Sites tab displays the sites that Android Studio checks for Android SDK and third-party updates. You can add other sites that host their own Android SDK addons, then download the SDK add-ons from those sites. Android Emulator The AVD Manager provides a graphical user interface in which you can create and manage Android Virtual Devices (AVDs), which are required by the Android Emulator. An Android Virtual Device (AVD) consists of a number of files including configuration and virtual storage required by the emulator. You can create as many AVDs as you want for simulating different devices. The following steps can be used to create an AVD in Eclipse − Step 1 − Select Window → AVD Manager. Step 2 − Click New. Step 3 − Type the name of the AVD, choose the target and specify values for the other features. Step 4 − Click Create AVD. For devices with keyboard, there is a standard set of mappings from the host keyboard to actions on the device. The default Emulator key mappings are − Emulator Key Mapping on Host Device BUTTON_CALL F3 BUTTON_HANGUP F4 BUTTON_HOME Home BUTTON_BACK Escape BUTTON_MENU F2, PageUp BUTTON_STAR Shift+F2, PageDown BUTTON_POWER F7 BUTTON_SEARCH F5 BUTTON_CAMERA Ctrl+Keypad_5, Ctrl+F3 BUTTON_VOLUME_UP Keypad_Plus, Ctrl+F5 BUTTON_VOLUME_DOWN Keypad_Minus, Ctrl+F6 TOGGLE_NETWORK F8 TOGGLE_TRACING F9 TOGGLE_FULLSCREEN Alt-Enter BUTTON_DPAD_CENTER Keypad_5 BUTTON_DPAD_UP Keypad_8 BUTTON_DPAD_LEFT Keypad_4 BUTTON_DPAD_RIGHT Keypad_6 BUTTON_DPAD_DOWN Keypad_2 TOGGLE_TRACKBALL F6 SHOW_TRACKBALL Delete CHANGE_LAYOUT_PREV Keypad_7, Ctrl+F11 CHANGE_LAYOUT_NEXT Keypad_9, Ctrl+ F12 ONION_ALPHA_UP Keypad_Multiply ONION_ALPHA_DOWN Keypad_Divide You can change these settings by editing the default.keyset file in the .android subdirectory. Android Debug Bridge ADB, Android Debug Bridge, is a command-line utility included with Google’s Android SDK. ADB can control your device over USB from a computer, copy files back and forth, install and uninstall apps, run shell commands, and more. If you have an emulator running and a real device connected, you must specify where you want the ADB commands to a real device, use the option − d and for the emulator, use –e. Following is the list of flags and commands for ADB. S.No. ADB flags & Description 1 -d Directs device to the only connected USB device; returns an error if more than one USB device is connected. 2 -e Directs command to the only running emulator; returns an error if more than one emulator is running. 3 -s <serial_number> Directs command the USB device or emulator with the given serial number. 4 devices List all connected devices 5 connect <host>:<port> Connect to a device via TCP/IP 6 disconnect <host>:<port> Disconnect from a TCP/IP device S.No. ADB commands & Description 1 adb push <local> <remote> Copy file/dir to device 2 adb pull <remote> [<local>] Copy file/dir from device 3 adb sync [<directory>] If <directory>is not specified, both /system and /data partitions will be updated. If it is “system” or “data”, only the corresponding partition is updated. 4 adb shell Run remote shell interactively 5 adb emu <command> Run emulator console command 6 adb logcat View device log 7 adb forward <local> <remote> Forward socket connections 8 adb install [-l] [-r] [-s] <file> Push this package file to device and install it. (-l forward lock the app) (-r reinstall the app, keeping its data) (-s install on SD card instead of internal storage) 9 adb uninstall [-k] <package> Remove this app package from the device. -k means keep the data and cache directories 10 adb bugreport Return all information from the device that should be included in the bug report. 11 adb help Show this help message 12 adb version Show version number The Shell A shell is a program that listens to keyboard input from the user and performs actions as directed by the user. The adb shell command provides Unix to send shell commands to an emulator or a connected device and display the results. It can also be used to launch an interactive shell locally. To issue a single command without entering a remote shell, use the shell command like this − adb [-d|-e|-s <serialNumber>] shell <shell_command> Or to enter a remote shell on an emulator/device − adb [-d|-e|-s <serialNumber>] shell When you are ready to exit the remote shell, press CTRL+D or type EXIT. Dalvik Debug Monitor Service Android ships a debugging tool, Dalvik Debug Monitor Service (DDMS). This tool provides additional services such as port-forwarding services, screen capture on device, incoming call and SMS spoofing etc. When DDMS starts, it connects to adb. A VM monitoring service is created between adb and DDMS, when a device is connected. This service notifies DDMS when a VM on the device is started or terminated. Once the VM starts running, its process id is sent to the DDMS via adb and the adb daemon opens a connection to the VM’s

SL4A – Exploring Android API ”; Previous Next SL4A is based on the Facade Design Pattern to communicate with the underlying Android API. This chapter explains the working of Façade Design Pattern and the different SL4A API facades. What is a Facade Design Pattern? A facade is an object that provides an interface that simplifies the access to the related interfaces in the application. In other words, a façade insulates the working of the libraries from the client and acts as an entry point to each subsystem level. Thus, the clients communicate only through their facades. The following illustration explains the same. SL4A and Android API Facades SL4A hosts interpreters for each language it supports. The interpreters access the underlying Android APIs through an interface called a façade. The following table lists the top-level facades and the functionality they provide − The following table lists the top-level facades and the functionality they provide − S.No. Android API Facade & Description 1 ActivityResultFacade It sets how your script will return information as an activity. This method implies that your script will return a result of some kind. The result type can be set to either RESULT_CANCELED(0) or RESULT_OK(-1) 2 AndroidFacade It provides access to common Android functions like reading input, notifications, launching application components etc. 3 ApplicationManagerFacade List all available and running packages, launch an activity, create your task manager or terminate a specific set of packages. 4 BatteryManagerFacade Exposes the battery manager and allows tracking battery status, health, type level, voltage etc. 5 BluetoothFacade Provides access to Bluetooth capabilities from basic connection features to sending and receiving both ASCII and binary data. This façade requires at least API level 5. 6 CameraFacade This method provides access to all camera-related functions. Allows taking a picture using the device’s camera and saving it to a specified path. It provides two functions namely cameraCapturePicture and cameraInteractiveCapturePicture. These functions are strictly for using the lens on the rear of the device. 7 CommonIntentsFacade Provides access to common Android Intents like opening a list of contacts, making a map search, starting an activity by action etc. 8 ContactsFacade Allows access to contacts such as providing the contact list for picking a contact, querying the contact list by attributes and getting a list of all contacts with their IDs and attributes. Some methods provided by the façade include contactsGet, pickContact, contactsGetById etc. 9 EventFacade The Android OS maintains an event queue for passing information between applications asynchronously. This façade provides functions to manage the event queue such as clearing the existing events, posting new events, listing, registering and unregistering broadcast signals etc. Examples of methods include eventPost, eventClearBuffer, etc. 10 EyesFreeFacade Available on devices below API level 4. It allows scripts to speak using text-to-speech technology. This façade is now replaced by TextToSpeechFacade. The only available function is ttsSpeak. 11 LocationFacade Provides functions that enables tracking the current location either by GPS or by using information about the cell tower you’re currently using. This feature requires an active internet connection to do the actual lookup. The façade provides methods like getLastKnownLocation, startLocating, stopLocating, readLocation etc. 12 MediaPlayerFacade Allows playing media files, controlling the media player, querying the current status of the media player and getting information about the media files. mediaIsPlaying, mediaPlayInfo and mediaPlayList returns the current state of the media player. A call to the startActivity function launches the media player. Functions like mediaPlay, mediaPlayPause, mediaPlayClose, mediaPlaySeek,mediaPlayStart and mediaPlaySetLooping are used to control the media player. 13 MediaRecorderFacade This façade provides audio and video recording capability. startInteractiveVideoRecording, recorderStartMicrophone, recorderCaptureVideo functions are used to launch and start audio/video recording respectively. To end a previously started recording call the recorderStop function. 14 PhoneFacade Makes available basic phone operations like tracking phone state, roaming status, initiating calls, SIM information etc. programmatically. Examples of methods include phoneCallNumber, phoneDialNumber, getCellLocation etc. 15 PreferencesFacade Allows access to shared preferences like getting the list of existing preferences and reading, modifying and adding new preferences. There are three functions supported by SL4A r4 release: prefGetAll, prefGetValue and prefPutValue. 16 SensorManagerFacade Allows tracking sensor data such as light,acceleration, magnetic field and orientation. To start/ stop sensing use the startSensing (deprecated and replaced with startSensingThreshold and startSensingTimed by SL4r4) and stopSensing function calls. readSensors, sensorsGetLight, sensorsReadAccelerometer, sensorsReadMagnetometer and sensorsReadOrientation are the functions provided by this façade. 17 SettingsFacade Provides access to different phone settings like ringer volume, screen brightness, airplane mode, vibration, media volume etc. Functions provided by this façade are checkAirplaneMode, checkRingersilentMode and checkScreenOn(atleast API level 7), getVibrateMode, setScreenTimeout, toggleVibrateMode setRingerVolume etc. 18 SignalStrengthFacade Allows monitoring phone signal strength. Call the startTrackingSignalStrengths function to start gathering data. Call the readSignalStrengths function to start gathering data. To shut down the process call the stoptrackingSignalStrengths function. It requires at least API level 7. 19 SmsFacade It has functions for deleting, reading, marking and sending SMS messages. Examples of functions provided by this façade include smsMarkMessageRead, smsDeleteMessage, smsSend etc. 20 SpeechRecognitionFacade Enables adding speech recognition functionality to the script. It has only one function named recognizeSpeech. 21 TextToSpeechFacade Provides TTS services for API4 and later. To have a device speak use the ttsSpeak function. To determine if the speak function has completed use the ttsIsSpeaking function. 22 ToneGeneratorFacade Generates DTMF tones for given digits. To use it you must call the generateDtmfTones function. 23 UiFacade Provides functions for creating user interface elements like textboxes, checkboxes, datepickers etc. It also allows interactive use of HTML pages. 24 WakeLockFacade Provides functions to create a wake lock include wakeLockAcquireBright, wakeLockAcquireDim, wakeLockAcquireFull and wakelockAcquirePartial. 25 WebCamFacade This façade requires at least API level 8. It allows streaming MJPEG streams from the front-facing device camera to the network. To start/stop the webcam use the webcamStart and the webcamStop functions respectively. To adjust the quality of the video while streaming use the webcamAdjustQuality function. 26 WifiFacade Helps you to control the Wi-Fi radio on your device. It allows scripts to query the status of Wi-Fi connectivity, search for access

SL4A – Configuring Your Device ”; Previous Next Installing SL4A At times, you may want to write scripts on the device and execute them. The Scripting Layer for Android helps achieve the same. To install SL4A on your device, follow the steps given below − Download the SL4A.apk file on your device. Launch the .apk file from the notifications screen. Select Install on the next screen to actually install SL4A. Alternatively, if you choose to use an emulator as against an android device, install SL4A using the browser inside the emulator. The SL4A installation initial screen on a device is shown below. Adding the Python Interpreter To install the python interpreter on a device, follow the steps given below − Step 1 − Start the SL4A application. Step 2 − Click the Menu button. Step 3 − A list of options will be displayed. Select View. Step 4 − Select the Interpreter option from the dialog box. Click Add. Step 5 − A list of interpreters available for download is displayed. Select Python 2.62 (or greater). To install python interpreter on an emulator, follow the steps given below − Step 1 − Ensure that the emulator is running in the background. Step 2 − Download python_for_android_rx.apk. Step 3 − In the terminal command-line shell, navigate to the location where the apk file is stored and type the following on the command line − adb install python_for_android_rx.apk SL4A supports scripting engine for multiple languages. A list of some language specific apk files are mentioned below − beanshell_for_android_rx.apk jruby_for_android_rx.apk lua_for_android_rx.apk perl_for_android_rx.apk python_for_android_rx.apk rhino_for_android_rx.apk Connecting to Windows OS Step 1 − Download and Install the USB Driver for Windows. Step 2 − Setup your device − Start SL4A from All apps screen on the device. Tap the Menu button → View. Choose the interpreters from the list. Tap the Menu button → Start Server. Select Public (to connect over Wi-Fi) or Private(to connect over USB). Step 3 − Add an environment variable (User variable) AP_PORT and value 9999. Android SDK and Eclipse have been discussed in the subsequent chapters. Print Page Previous Next Advertisements ”;

SL4A – Useful Resources ”; Previous Next The following resources contain additional information on SL4A. Please use them to get more in-depth knowledge on this. Useful Links on SL4A SL4A Wiki − Wikipedia Reference for SL4A. Useful Books on SL4A To enlist your site on this page, please drop an email to [email protected] Print Page Previous Next Advertisements ”;

SL4A – Background Scripting with Python ”; Previous Next A service is a component, which runs in the background, without direct interaction with the user. It does not have any UI (user interface). The service runs in the background indefinitely even if application is destroyed. This chapter describes the writing scripts that perform specific tasks in the background. Background Tasks SL4A enables a script to run in a terminal or in the background. To launch a script in the background choose the icon that looks like a cog wheel. The script runs in the background infinitely. However, one may choose to explicitly shut down such services. Launch on Boot Scripts These scripts are launched whenever the device boots. The Launch on Boot preferences screen is an application that lets you specify the device’s boot preferences. The utility supports execution of multiple scripts via a Master script. The Master script launches the other scripts. Triggers A trigger defines a set of actions that must be performed in response to an action/event. Triggers may be added as well as deleted. The /sdcard/sl4a/scripts directory allows you to choose a script to run when an event is triggered. The list of options that may trigger you script includes battery, location, phone, sensors and signal strength. Orientation-based Actions SL4A lets us run scripts depending on the orientation and movement of the device. The startSensingTimedAPI is used to determine the orientation and movement of the device. The following snippet uses TTS function to notify the user when the phone has been placed face down − import android,time droid = android.Android() droid.startSensing() while True: res = droid.sensorsGetLight().result if res is not None and res <=10: droid.ttsSpeak(“Device faced down!!”) time.sleep(5) Location-based Actions Library, church are the locations that you may frequently visit and you definitely want to silence your phone when you are there. SL4A allows you to build scripts that will track your location and take specific actions. Time-based / Elapsed-Time-based Triggers These triggers are used to perform actions at a specific time of day. The 24-hour time format should be used to specify the time. Examples include a script to set alarm, reminders etc. As against a time-based trigger, an elapsed time-based trigger executes the script after an elapsed number of time. The snooze option on an alarm application is based on this concept. Print Page Previous Next Advertisements ”;

Discuss SL4A ”; Previous Next The Scripting Layer for Android (SL4A) is a library that helps write scripts targeting the Android Platform. SL4A supports a number of scripting languages like Perl, Python, JRuby, PHP etc. It can also be extended to support new languages. While Java can be used for Android Development, it is a good thing when all you need to do is write a simple test case or turn on or off settings on your device. This tutorial will help you automate your Android device using simple Python scripts. Print Page Previous Next Advertisements ”;

SL4A – Android Architecture ”; Previous Next The Android software stack comprises of different layers, each layer manifesting well-defined behavior and providing specific services to the layer above it. The following figure presents a broad architecture of Android with its primary components. Linux Kernel Android is built on the Linux kernel code modified to run on embedded systems as against the traditional Linux system. Hardware drivers for many common devices are built into the kernel, thereby ensuring device portability. It is based on secure user based permission model, which prevents one application from reading another application’s information or from interfering with its execution (e.g. CPU, memory, devices etc.). Group ID based access to networking and Bluetooth features, logger, alarm, power management, low memory killer, Binder IPC mechanisms are a few noted enhancements to the Kernel. Libraries and Runtime This forms the second layer of the architecture. It includes a set of hardware optimized C, C++ libraries, also referred to as the native layer. Examples include Media Libraries, SQLite, SSL, Bionic, WebKit etc. The Android Runtime comprises of two different components − the Dalvik VM and Core Libraries. The Dalvik VM provides an execution environment for the applications on the Android Platform. The set of core libraries provides most of the functionality available in Java APIs. Application Framework This layer makes available the Libraries as services to the applications. Some most important components within this layer include Location Manager, Resource Manager, Activity Manager and Notification Manager. Applications By default, Android comes with a rich set of applications, including the browser, SMS program, calendar, contact manager, maps etc. Google Play provides alternatives to these applications, if the user desires so. Building Blocks An application can interface with the system with four function blocks. They are as follows − Activities − Activities represent a single screen that the user sees or interacts with visually. For example, an email app might have one activity that shows a list of new emails, another activity to compose an email, and another activity for reading emails. Services − A majority of processing is done by these services for your application. It is the logic behind the user interface. For example, a service might play music in the background while the user is in a different app, or it might fetch data over the network without blocking user interaction with an activity. Broadcast Receivers − A component that can be registered to listen for system or application events and issue notifications about the same. An instance for broadcast originating from the system is a ‘low battery notification’ while an application level broadcast could be a ‘download successful’ notification. Content Providers − A content provider manages and helps you share data between multiple applications. For e.g. a content provider may be used to share the contacts data. These components interact with each other through messages called Intents. Print Page Previous Next Advertisements ”;

SL4A – Python Library ”; Previous Next Python has a standard library, which includes a wide variety of routines that help you code and reuse these codes easily. A Module is a Python file that has definitions of variables and a set of related routines or functions. Some of the core Modules provided by the Python library are as follows − Built-in Functions and Exceptions − Python imports both these modules when it starts up and makes their content available for all programs. The built-in module defines built-in functions like len, int, range, while the exceptions module defines all built-in exceptions. Operating System Interface Modules − The OS module makes available, the functions that enables performing OS level operations through scripts. Type Support Modules − Type support modules include string module-to implement, commonly used string operations; math module provides mathematical operations etc. Regular Expressions − Regular Expressions are string patterns written in a specific syntax, which can be used to match or extract strings or substrings. The re module provides Regex support for Python. Language Support Modules − The sys module gives you access to various interpreter variables, such as the module search path, and the interpreter version. The operator module provides functional equivalents to many built-in operators. The copy module allows you to copy objects. Finally, the gc module gives you more control over the garbage collector facilities in python 2.0. About JSON The JavaScript Object Notation (JSON) is a data-interchange format. Though many programming languages support JSON, it is especially useful for JavaScript-based apps, including websites and browser extensions. JSON can represent numbers, Booleans, strings, null, arrays (ordered sequences of values), and objects (string-value mappings) made up of these values (or of other arrays and objects). Print Page Previous Next Advertisements ”;

SL4A – Quick Guide ”; Previous Next SL4A – Android Overview Android is a Linux based operating system, designed primarily for portable devices like smartphones and tablet. Android is more than an operating system. It is a software stack that provides many features for users, developers and manufacturers. Android Version Features Android (Alpha) 1.0 First version of Android Android 1.5 (Cupcake) Added auto-rotation option, copy and paste feature added in the web browser Android 1.6 (Donut) Voice search and Search box were added Android 2.0/2.1 (Éclair) Bluetooth 2.1 support Android 2.2/2.2.3(Froyo) Support for Adobe Flash 10.1 Android 2.3/2.3.7 (Gingerbread) Internet calling, one touch word selection and copy/paste Android 3.0/3.2.6 (Honeycomb) This version is available only for tablets.Features include support for multi-core processors, ability to encrypt all user data Android 4.0/4.0.4 (Ice cream sandwich) Virtual button in the UI, ability to shut down apps that are using data in the background Android 4.1/4.3.1 (Jelly Bean) Based on Linux Kernel 3.0.31? Smoother User Interface, Bluetooth data transfer for Android Beam Android 4.4/4.4.4,4.4W/4.4W.2 (KitKat) Integration with cloud storage, Built-In sensors, Lock Art Screen Android 5.0/5.1.1 (Lollipop) Improved RAM and Battery Management, Fixes for sudden App closure, issues with wireless connections, notifications etc. It is open source and business friendly. The user can choose to replace built-in applications with applications of their choice. Many versions of Android have been released since its original release. SL4A – Android Architecture The Android software stack comprises of different layers, each layer manifesting well-defined behavior and providing specific services to the layer above it. The following figure presents a broad architecture of Android with its primary components. Linux Kernel Android is built on the Linux kernel code modified to run on embedded systems as against the traditional Linux system. Hardware drivers for many common devices are built into the kernel, thereby ensuring device portability. It is based on secure user based permission model, which prevents one application from reading another application’s information or from interfering with its execution (e.g. CPU, memory, devices etc.). Group ID based access to networking and Bluetooth features, logger, alarm, power management, low memory killer, Binder IPC mechanisms are a few noted enhancements to the Kernel. Libraries and Runtime This forms the second layer of the architecture. It includes a set of hardware optimized C, C++ libraries, also referred to as the native layer. Examples include Media Libraries, SQLite, SSL, Bionic, WebKit etc. The Android Runtime comprises of two different components − the Dalvik VM and Core Libraries. The Dalvik VM provides an execution environment for the applications on the Android Platform. The set of core libraries provides most of the functionality available in Java APIs. Application Framework This layer makes available the Libraries as services to the applications. Some most important components within this layer include Location Manager, Resource Manager, Activity Manager and Notification Manager. Applications By default, Android comes with a rich set of applications, including the browser, SMS program, calendar, contact manager, maps etc. Google Play provides alternatives to these applications, if the user desires so. Building Blocks An application can interface with the system with four function blocks. They are as follows − Activities − Activities represent a single screen that the user sees or interacts with visually. For example, an email app might have one activity that shows a list of new emails, another activity to compose an email, and another activity for reading emails. Services − A majority of processing is done by these services for your application. It is the logic behind the user interface. For example, a service might play music in the background while the user is in a different app, or it might fetch data over the network without blocking user interaction with an activity. Broadcast Receivers − A component that can be registered to listen for system or application events and issue notifications about the same. An instance for broadcast originating from the system is a ‘low battery notification’ while an application level broadcast could be a ‘download successful’ notification. Content Providers − A content provider manages and helps you share data between multiple applications. For e.g. a content provider may be used to share the contacts data. These components interact with each other through messages called Intents. SL4A – Scripting Layer for Android Android scripting is a handy tool for simple tasks such as automation and prototyping as against using the Java programming language for the same. The Scripting Layer for Android (SL4A) provides a platform for multiple scripting solutions on the android platform. What is SL4A? The Scripting Layer for Android (SL4A) is a library that provides a platform to write simple scripts to automate tasks on an android device using languages other than JAVA. SL4A, originally called Android Scripting Environment (ASE), was first announced on the Google Open Source blog in June 2009. The project saw the light of the day primarily through the efforts of Damon Kohler and it has grown through the contributions of other developers. It supports most popular scripting languages. These include − Beanshell 2.0b4 JRuby 1.4 Lua 5.1.4 Perl 5.10.1 PHP 5.3.3 Python Rhino 1.7R2 Javascript TCL Why SL4A – Scripting Languages Vs JAVA One of the first questions one would probably ask is, “Why use SL4A instead of Java?” Firstly, not everyone is a fan of Java. Scripting languages provide an easy programming environment as compared to Java. Secondly, the language requires the use of an edit/compile/run design loop. This means that you edit, re-compile and then run the application each time you desire some modification. On the contrary, scripts are interpreted and executed on the fly. Moreover, SL4A even makes it possible, in many cases, to reuse code written for a desktop environment. The following figure illustrates scripts written in Python targeting SL4A and in Java respectively. SL4A – Architecture SL4A has three main components. They are as follows − Script Interpreters Android RPC Client Facades In this chapter, we will discuss more about these three components. Script Interpreters