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App Development for Android

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?. Development Tools. (Android) Java

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App Development for Android

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  1. App Development for Android PrabhakerMateti

  2. 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?

  3. 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

  4. The Emulator • QEMU-based ARM emulator • Displays the same image as the device • Limitations: • No Camera support

  5. 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.

  6. 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

  7. 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

  8. 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

  9. Android Architecture

  10. Android Architecture

  11. 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

  12. Linux Kernel Enhancements • Alarm • Ashmem (Anonymous SHaredMEMory) • 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)

  13. 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…

  14. 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, …

  15. 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.

  16. 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, ...)

  17. 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/

  18. 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]

  19. 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.

  20. Android Application Internals

  21. 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.

  22. 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.

  23. .apk Internals • AndroidManifest.xml — deployment descriptor for applications. • IntentReceiver as advertised by the IntentFiltertag. • *.java files implement Android activity • Main.xml — visual elements, or resources, for use by activities. • R.java —automatically generated by Android Developer Tools and "connects" the visual resources to the Java source code. • Components share a Linux process: by default, one process per .apk file. • .apk files are isolated and communicate with each other via Intents or AIDL.

  24. 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

  25. 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

  26. Life cycle of an Android activity

  27. 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.

  28. 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.

  29. 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).

  30. 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()

  31. 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.

  32. 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.

  33. Content Providers Application Activity Activity Application Application Activity Content Resolver Service Content Resolver Content Provider Content Resolver Data XML Remote Store SQLite

  34. 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 

  35. 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.

  36. Intent Filters

  37. IntentReceivers • Components that respond to broadcast ‘Intents’ • Way to respond to external notification or alarms • Apps can invent and broadcast their own Intent

  38. Example App: Hello World! developer.android.com/resources/tutorials/hello-world.html

  39. Goal • Create a very simple application • Run it on the emulator • Examine its structure

  40. Package Content All source code here Java code for our activity Generated Java code Helps link resources to Java code All non-code resources Layout of the activity Images Strings used in the program Android Manifest

  41. Android Manifest • <?xml version="1.0" encoding="utf-8"?> • <manifest xmlns:android="http://schemas.android.com/apk/res/android" • package="com.example.helloandroid" • android:versionCode="1" • android:versionName="1.0"> • <application android:icon="@drawable/icon"android:label="@string/app_name"> • <activity android:name=".HelloAndroid" • android:label="@string/app_name"> • <intent-filter> • <action android:name="android.intent.action.MAIN" /> • <category android:name="android.intent.category.LAUNCHER" /> • </intent-filter> • </activity> • </application> • </manifest>

  42. 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);TextViewtv = new TextView(this);tv.setText("Hello, Android – by hand");setContentView(tv);   }} Set the view “by hand” – from the program

  43. Run it!

  44. 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 view as described in the main.xml layout

  45. /res/layout/main.xml <?xml version="1.0" encoding="utf-8"?> <LinearLayoutxmlns: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

  46. /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>

  47. /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;    }}

  48. Run it!

  49. 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);    }}

  50. Run it!

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