App Development for Android

Prabhaker Mateti

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CEG 436 Specifics

• Because CEG 436 is a 10-week term course skipped for now refreshers on– Operating Systems– TCP/IP Networking– Cellular Telephony

• “Definitions”– Mobile Devices/Smart Phone– What is Android?

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Development Tools

• (Android) Java– Java syntax is the same. But, not all libs are included.– Unused: Swing, AWT, SWT, lcdui

• Eclipse– www.eclipse.org/

• ADT Plugin for Eclipse– developer.android.com/sdk/eclipse-adt.html

• Android SDK– developer.android.com/sdk/tools-notes.html

• Android Device Emulator• Development Platforms: Linux, Mac OSX, or Windows

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The Emulator• QEMU-based ARM

emulator• Displays the same

image as the device• Limitations:

– No Camera support

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Debugging• adb acts as a middleman between a device and your development system. It

provides various device management capabilities, including moving and syncing files to the emulator, running a UNIX shell on the device or emulator, and providing a general means to communicate with connected emulators and devices.

• Dalvik Debug Monitor Server DDMS is a graphical program that communicates with your devices through adb. DDMS can capture screenshots, gather thread and stack information, spoof incoming calls and SMS messages, and has many other features.

• Device or Android Virtual Device An adb device daemon runs on the device or emulator and provides a means for the adb host daemon to communicate with the device or emulator.

• JDWP debugger The Dalvik VM supports the JDWP protocol to allow debuggers to attach to a VM. Java IDEs include a JDWP debugger, or you can use a command line debugger such as jdb.

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Android Application Package• res/layout: declaration layout

files• res/drawable: intended for

drawing• res/anim: bitmaps, animations

for transitions• res/values: externalized values

– strings, colors, styles, etc• res/xml: general XML files

used at runtime• res/raw: binary files (e.g.,

sound)

• An application consists of:

Java Code

Data Files

Resources Files

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Android Application Package

• Using Java/Eclipse/ADT develop several source code files.

• An Android application is bundled by the “aapt” tool into an Android package (.apk)– An .apk file is a zip file. Invoke unzip if you wish.

• “Installing” an Application is a built-in op of Android OS.– May need to enable the trustworthiness of

developer

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A Launcher: zeam-2.9.0.apk• ( … a highly incomplete list … )• res/anim/apps_fade_in.xml• res/color/bright_text_dark_focused.xml• res/drawable/box_launcher_top.xml• res/drawable/timepicker_up_selected.9.png• res/layout/application_list.xml• res/xml/preferences.xml• AndroidManifest.xml• resources.arsc• res/drawable-hdpi/action_notifications.png• res/layout-land/application.xml• classes.dex• META-INF/MANIFEST.MF• META-INF/CERT.SF • META-INF/CERT.RSA

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Android Architecture

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Android Architecture

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Linux Kernel

• Works as a Hardware Abstraction Layer (HAL)• Device drivers

– Keypad, Display, Power Mgmt, FlashMem, Binder, WiFi, Audio, Camera

• Memory management• Process management• Networking

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Linux Kernel Enhancements• Alarm• Ashmem (Anonymous SHared MEMory)

– ashmem uses virtual memory, whereas pmem (process memory allocator) uses physically contiguous memory

• Binder– an Android-specific inter-process communication mechanism, and remote

method invocation system.• Power Management• Low Memory Killer

– echo "1536,2048,4096,15120,15360,23040" > /sys/module/lowmemorykiller/parameters/minfree

• Kernel Debugger• Logger (system logging facility)

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Android Runtime

• Dalvik VM– a newly developed Java Virtual Machine– dx tool translates .class files to .dex files– Compact compared to .class files– Optimized for memory and battery power

• Core Libraries– Java Std Edition– Collections, I/O etc…

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Libraries

• Surface Manager: A compositing window manager similar to Compiz. Instead of drawing directly to the screen buffer, drawing commands go into off-screen bitmaps that are then combined with other bitmaps to form the display the user sees. Can create see-through windows, fancy transitions, …

• 2D and 3D graphics: Use 3D hardware or a software renderer. OpenGL.

• Media codecs: AAC, AVC (H.264), H.263, MP3, MPEG-4, …

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Libraries

• SQLite database engine– Provides persistent storage. – Also used in Firefox and the iPhone.

• Browser engine: – WebKit library for rendering web pages– the same engine is used in KDE, the Google

Chrome browser, Apple’s Safari browser, the iPhone, and Symbian 60.

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Android NDK: Native C/C++ libraries

• C/C++ libraries• not the full glibc as in Linux distros

• Supported CPUs: ARM, x86– libc (C library) headers– libm (math library) headers– JNI interface headers– libz (Zlib compression) headers– liblog (Android logging) header– OpenGL ES headers– libjnigraphics (Pixel buffer access) header– A Minimal set of headers for C++ support– OpenSL ES native audio libraries– Android native application APIS

• Cross-toolchains (compilers, linkers, ...)

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OpenGL ES

• OpenGL ES is a subset of OpenGL graphics standard.– low-level interface for graphics acceleration. – floating-point and fixed-point systems.

• OpenGL ES 1.X is for fixed function hardware and offers acceleration, image quality and performance.

• OpenGL ES 2.X enables full programmable 3D graphics.• OpenGL SC is tuned for the safety critical market.• http://www.khronos.org/opengles/

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Application Framework• Views lists, grids, text boxes, buttons, and even an

embeddable web browser• Content Providers to access data from other applications

(such as Contacts), or to share their own data• A Resource Manager, providing access to non-code

resources such as localized strings, graphics, and layout files• A Notification Manager that enables all applications to

display custom alerts in the status bar• An Activity Manager that manages the lifecycle of

applications and provides a common navigation backstack [sic]

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Standard Applications

• Android provides a set of core applications:– Email Client– SMS Program– Calendar– Maps– Browser– Contacts– Etc

• All applications are written using the Java language.

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Android Application Internals

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Application Fundamentals

• Each application is a different “user”.• Each application gets a unique Linux user ID.

The system sets permissions for all the files in an application so that only the user ID assigned to that application can access them.

• Each process has its own Dalvik VM.• Every application runs in its own Linux

process. A process can have multiple threads.

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Application Components• Activity

– represents a single screen with a user interface.• Service

– runs in the background; Long-running; for remote processes– no user interface.

• Content provider – manages a shared set of application data.

• Broadcast receiver – responds to broadcast announcements.

• An application can have multiple instances of the above four types.• Each component is a different point through which the system can enter

an application.• Every component has a managed lifecycle.

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.apk Internals1. AndroidManifest.xml — deployment descriptor for applications.2. IntentReceiver as advertised by the IntentFilter tag.3. *.java files implement Android activity4. Main.xml — visual elements, or resources, for use by activities.5. R.java —automatically generated by Android Developer Tools and

"connects" the visual resources to the Java source code.6. Components share a Linux process: by default, one process

per .apk file.7. .apk files are isolated and communicate with each other via

Intents or AIDL.

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Application Resources

• anything relating to the visual presentation of the application– images, animations, menus, styles, colors, audio

files, …• resource ID• alternate resources for different device

configurations

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AndroidManifest.xml• Declares all application components:

– <activity>– <service>– <provider> for content providers– <receiver> for broadcast receivers

• The manifest can also:– Identify any user permissions the application requires, such as

Internet access or read-access to the user's contacts.– Declare hardware and software features used or required by

the application– API libraries the application needs

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Life cycle of an Android activity

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Activity

• Typically, one of the activities is marked as the first one that should be presented to the user when the application is launched.

• Created “Activity” must be defined into the application’s manifest.

• An activity is usually a single screen:– Implemented as a single class extending Activity.– Displays user interface controls (views).– Reacts on user input/events.

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Activity• An application

typically consists of several screens:– Each screen is

implemented by one activity.

– Moving to the next screen means starting a new activity.

– An activity may return a result to the previous activity.

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Service

• A service does not have a visual user interface, but rather runs in the background for an indefinite period time.– Examples: music player, network download, etc

• Each service extends the Service base class.• It is possible to bind to a running service and start the

service if it's not already running.• While connected, it is possible communicate with the

service through an interface defined in AIDL (Android Interface Definition Language).

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Services• Similar to daemons in Linux/Unix or Windows services.• Interprocess communication (IPC).• A service is "started" when a component does a startService

(). Stops with stopSelf() or stopService()• A service is "bound" when a component does a bindService

(). Multiple components can bind to the service at once. When all of them unbind, the service is destroyed.

• Can work both ways. (i) onStartCommand() allows components to start it and (ii) onBind() allows binding.

• (iii) onCreate() (iv) onDestroy()

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Broadcast Receivers

• A broadcast receiver is a component that receives and reacts to broadcast announcements (Intents).

• All receivers extend the BroadcastReceiver base class.

• Many broadcasts originate in system code.– the time zone has changed– the battery is low

• Applications can also initiate broadcasts.CEG436

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Content Providers

• Enables sharing of data across applications– E.g. address book, photo gallery– the only way to share data between applications.

• Provides uniform APIs for query, delete, update and insert.

• Applications do not call these methods directly.– They use a ContentResolver object and call its methods

instead.– A ContentResolver can talk to any content provider.

• Content is represented by URI and MIME type.

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Content Providers

Activity

ApplicationActivity

Application

Activity

Content Provider

Service

Application

Data SQLite XML Remote Store

Content Resolver Content Resolver

Content Resolver

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Intent• Intents are system messages that notify applications of various events:

– Activity events ( launch app, press button)– Hardware state changes (acceleration change, screen off, etc)– Incoming data (Receiving call, SMS arrived)

• An intent object is an action to be performed on some data Uri. It provides runtime binding between the code in different applications.

• Examples:– ACTION_DIAL content://contacts/people/13

• Display the phone dialer with the person #13 filled in.– ACTION_VIEW content://contacts/people/

• Display a list of people, which the user can browse through.– startActivity(new Intent(Intent.VIEW_ACTION, Uri.parse( "http://www.fhnw.ch"));– startActivity(new Intent(Intent.VIEW_ACTION, Uri.parse("geo:47.480843,8.211293"));– startActivity(new Intent(Intent.EDIT_ACTION, Uri.parse("content://contacts/people/1"));

• secondary attributes: category, type, component, extras

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public class Intent• startActivity to launch an activity.• broadcastIntent to send it to a BroadcastReceiver• Communicate with a Service

– startService(Intent) or – bindService(Intent, ServiceConnection, int)

• Explicit Intents specify a component to be run.– setComponent(ComponentName) or– setClass(Context, Class))

• Implicit Intents match an intent against all of the <intent-filter>s in the installed applications.– Will return to this topic later.

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Intent Filters

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IntentReceivers

• Components that respond to broadcast ‘Intents’

• Way to respond to external notification or alarms

• Apps can invent and broadcast their own Intent

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Example App: Hello World!

developer.android.com/resources/tutorials/hello-world.html

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Goal

• Create a very simple application

• Run it on the emulator• Examine its structure

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Package Content

Java code for our activityAll source code here

Generated Java codeHelps link resources to Java code

Layout of the activity

Strings used in the program

All non-code resources

Android Manifest

Images

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Android Manifest1. <?xml version="1.0" encoding="utf-8"?>2. <manifest xmlns:android="http://schemas.android.com/apk/res/android"3. package="com.example.helloandroid"4. android:versionCode="1"5. android:versionName="1.0">6. <application android:icon="@drawable/icon" android:label="@string/app_name">7. <activity android:name=".HelloAndroid"8. android:label="@string/app_name">9. <intent-filter>10. <action android:name="android.intent.action.MAIN" />11. <category android:name="android.intent.category.LAUNCHER" />12. </intent-filter>13. </activity>

14. </application>

15. </manifest>

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HelloAndroid.java package com.example.helloandroid;

import android.app.Activity;import android.os.Bundle;import android.widget.TextView;

public class HelloAndroid extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); TextView tv = new TextView(this); tv.setText("Hello, Android – by hand"); setContentView(tv); }} Set the view “by

hand” – from the program

Inherit from the Activity Class

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Run it!

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HelloAndroid.javapackage com.example.helloandroid;import android.app.Activity;import android.os.Bundle;public class HelloAndroid extends Activity {

/** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState); setContentView(R.layout.main); }

}

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Set the layout of the view as described in the main.xml layout

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/res/layout/main.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" > <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/hello" /></LinearLayout>

Further redirection to /res/values/strings.xml

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/res/values/strings.xml

<?xml version="1.0" encoding="utf-8"?><resources> <string name="hello">Hello World, HelloAndroid – by resources!</string> <string name="app_name">Hello, Android</string></resources>

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/gen/R.java package com.example.helloandroid;

public final class R { public static final class attr { } public static final class drawable { public static final int icon=0x7f020000; } public static final class id { public static final int textview=0x7f050000; } public static final class layout { public static final int main=0x7f030000; } public static final class string { public static final int app_name=0x7f040001; public static final int hello=0x7f040000; }}

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Run it!

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Introduce A Bug package com.example.helloandroid;

import android.app.Activity;import android.os.Bundle;

public class HelloAndroid extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); Object o = null; o.toString(); setContentView(R.layout.main); }}

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Run it!

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Case Studies of Applications

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ADW.Launcher

• ADW.Launcher is an open source Home Replacement app. it is included as the main Launcher in Cyanogen's custom ROMs.

• I will be (??) using the source code of this app as a running example. – Download the source from

http://code.google.com/p/adw-launcher-android/

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Project Suggestions

• Augmented Campus Reality– camera + maps + compass = heads up info

• Games– multi-player (bluetooth, wifi, cell)– location-based (scavenger hunt)

• Custom overlays for maps– weather, traffic, friends

• Web scraping– news filters– sport scores– dook news eliminators– more on next slide …

• Distributed computing?– 10,000 phones all donating their idle time– tiny terminal (phone) + fast cpu/network (server)

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Project Suggestions– Web Scrapers [movies, weather, sports, <topic> news]

• Find multiple web sources• Scrape them for the relevant information• Present in a custom UI on the phone

– Asynchronous games [chess, poker, risk]• Develop an API for all games to communicate through

– Establish connections by phone number– Send and receive game data– Ability to reopen connections

– Planner/To-do list with location data• Decide route to next class, meeting, etc• Find a order/route for non time-critical tasks• Connect to campus directory to find teachers/classmates

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Source Code for Android Examples

• Sources for many Android applications that can be enhanced:

• http://code.google.com• http://developer.android.com/resources/brow

ser.html?tag=sample

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