App Development for Android
Prabhaker Mateti
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
• An application consists of:
Java
Code
Data Files
Resources
Files
•
res/xml: general XML files
used at runtime
• res/raw: binary files (e.g.,
sound)
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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
•
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( … 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
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:
–
–
–
–
–
–
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Email Client
SMS Program
Calendar
Maps
Browser
Contacts
Etc
• All applications are written using the Java
language.
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Android Application Internals
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 Internals
1. AndroidManifest.xml — deployment descriptor for
applications.
2. IntentReceiver as advertised by the IntentFilter tag.
3. *.java files implement Android activity
4. 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.
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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
Application
Activity
Activity
Application
Application
Activity
Content Resolver
Service
Content Resolver
Content Provider
Content Resolver
Data
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SQLite
XML
Remote
Store
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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
Goal
• Create a very simple
application
• Run it on the emulator
• Examine its structure
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Package Content
All source code here
Java code for our activity
Generated Java code
Helps link resources to
Java code
Layout of the activity
All non-code
resources
Images
Strings used in the
program
Android Manifest
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Android Manifest
1. <?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
Inherit
from the
Activity
Class
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
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hand” – from the
program
Run it!
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HelloAndroid.java
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);
setContentView(R.layout.main);
}
}
Set the layout of the
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view as described in
the main.xml layout
/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
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
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• 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)
• Shared whiteboard
53
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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