Transcript Operating System Support for Mobile Devices

Mobile Software Development
Framework: Android
2/23/2011
Y. Richard Yang
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Admin.
 Homework 2 due today
 Please schedule time to meet with the TA to
demo your program
 Midterm: Wednesday after spring break
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Recap: Mobile Programming Requirements
Handle heterogeneous devices/configurations
 Be extremely efficiency on using resources
(memory, battery, …)
 Easy programming for event-driven programming
…

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Recap: tinyOS
 Customized OS for each app.
 Reusability achieved through
 Components and interfaces structure
 Execution model: two threads
 One for tasks
 One for event handling
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HelloWorldMIDlet.java
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
public class HelloWorldMIDlet extends MIDlet
implements CommandListener {
private Command exitCommand;
private Display display;
private TextBox t;
public HelloWorldMIDlet() {
display = Display.getDisplay(this);
exitCommand = new Command("Exit", Command.EXIT, 2);
t = new TextBox(“CS434", "Hello World!", 256, 0);
t.addCommand(exitCommand);
t.setCommandListener(this);
}
public void startApp() { display.setCurrent(t); }
public void pauseApp() { }
public void destroyApp(boolean unconditional) { }
public void commandAction(Command c, Displayable s) {
if (c == exitCommand) {
destroyApp(false);
notifyDestroyed();
}
}
}
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Recap: J2ME
 Scale down a popular programming environment to
ease learning
 Use virtual machines to mask device heterogeneity
 Use configuration/profile to handle device
heterogeneity to avoid using lowest common
denominator
 MIDLet and Displayable to support user-interface
driven applications


MIDLet manages app life cycle
Displayable has commands and provides command listener
 Introduce persistent record store
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Recap: Android
 Scale down a popular programming
environment to ease learning
 Use virtual machines to mask device
heterogeneity
 Activity and View
Activity
 A screen
with which
users can
interact
 Activity has
life cycle to
yield resources
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View
 A view component is a building block for user
interface components.
 Widget Toolbox
 TextView,

EditText, Button, Form, TimePicker…
ListView
 Layout
• Positions of controls
• LinearLayout, Relativelayout
http://developer.android.com/guide/tutorials/views/index.htm
View by XML
 Layout of visual interface
 Java Code
 Initialize
@Override
public void onCreate(Bundle icicle) {
super.onCreate(icicle);
setContentView(R.layout.main);
}

Access
TextView myTextView =
(TextView)findViewById(R.id.myTextView);
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:id=”@+id/myTextView”
android:layout_width=”fill_parent”
android:layout_height=”wrap_content”
android:text=”Hello World, HelloWorld”
/>
</LinearLayout>
User Interaction Event
 onKeyDown. onKeyUp
 onTrackBallEvent
 onTouchEvent
registerButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View arg0) {….}}
myEditText.setOnKeyListener(new OnKeyListener() {
public boolean onKey(View v, int keyCode, KeyEvent event) {
if (event.getAction() == KeyEvent.ACTION_DOWN)
if (keyCode == KeyEvent.KEYCODE_DPAD_CENTER) {
…
return true;
}
return false;
}});
}
Example: TipCal
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Application Framework (Android):
Key Concepts
 Activity and view

Visible screen for user interaction
 External resources
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External Resources
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Application Framework (Android):
Key Concepts
 Activity and view

Visible screen for user interaction
 External resources
 Service
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Service: Working in Background
 A basic function of Android Service:



A facility for an application to tell the system about something it
wants to be doing in the background (even when the user is not
directly interacting with the application).
The system to schedule work for the service, to be run until the
service or someone else explicitly stop it.
NO GUI, higher priority than inactive Activities
 Note


A Service is not a separate process. The Service object itself
does not imply it is running in its own process; unless otherwise
specified, it runs in the same process as the application it is part
of.
A Service is not a thread. It is not a means itself to do work off
of the main thread (to avoid Application Not Responding errors).
Application Framework (Android):
Key Concepts
 Activity and view

Visible screen for user interaction
 External resources
 Service
 Intercommunications
Communication
among apps:
- Intent
- broadcast
- data provider
App
App
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Application and Component Glues
 Intent
An intent is an abstract description of an
operation to be performed.
 To invoke operations from your own or others
 Can pass data back and forth between app.

 Intent Filter

Register Activities, Services, and Broadcast
Receivers as being capable of performing an
action on a particular kind of data.
Intent Description
<Component name>
 Action

Data
 Category, e.g., LAUNCHER

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Intent Usage
 Pass to Context.startActivity() or
Activity.startActivityForResult() to launch an activity or get an
existing activity to do something new.
 Pass to Context.startService() to initiate a service or deliver
new instructions to an ongoing service.
 Pass to Context.bindService() to establish a connection
between the calling component and a target service. It can
optionally initiate the service if it's not already running.
 Pass to any of the broadcast methods (such as
Context.sendBroadcast(), Context.sendOrderedBroadcast(), or
Context.sendStickyBroadcast()) are delivered to all interested
broadcast receivers. Many kinds of broadcasts originate in
system code.
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Android: Broadcast Receiver
 Sending a broadcast:
 Context.sendBroadcast(Intent intent,
String receiverPermission)
 Context.sendOrderedBroadcast()
 Receiving broadcast:
 Intent registerReceiver
(BroadcastReceiver receiver,
IntentFilter filter)
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Intent Resolution: Explicit
 Explicit intents: component identified
Intent myIntent = new Intent(IntentController.this,
TipCal.class);
startActivity(myIntent);
 Make sure AndroidManifest.xml announces
activities to be started
<application android:icon="@drawable/icon" android:label="@string/app_name">
<activity android:name=".IntentController"
android:label="Intent1">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".TipCal"></activity>
</application>
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Intent Resolution: Implicit
 Implicit intents

System matches an intent object to the intent
filters of others
http://developer.android.com/guide/topics/intents/intents-filters.html
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Intent filter
action
category
data
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Intent Example II: Implicit
String action = "android.intent.action.VIEW";
Uri data = Uri.parse("http://www.google.com");
Intent myIntent = new Intent(action, data);
startActivity(myIntent);
 AndroidManifest.xml file for com.android.browser
<intent-filter>
<action android:name="android.intent.action.VIEW" />
<category android:name="android.intent.category.DEFAULT" />
<scheme android:name="http" />
<scheme android:name="https" />
<scheme android:name="file" />
</intent-filter>
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Intent Example II: Implicit
String action = "android.intent.action.DIAL";
String phno = "tel:4326400";
Uri data = Uri.parse(phno);
Intent dialIntent = new Intent(action, data);
startActivity(dialIntent);
A Design Template: Invoker
String action = “com.hotelapp.ACTION_BOOK";
String hotel = “hotel://name/“ + selectedHotel;
Uri data = Uri.parse(hotel);
Intent bookingIntent = new Intent(action, data);
startActivityForResults(bookingIntent, requestCode);
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A Design Template: Provider
<activity android:name=".Booking" android:label=“Booking">
<intent-filter>
<action android:name=“com.hotelapp.ACTION_BOOK" />
<data android:scheme=“hotel" android:host=“name”/>
</intent-filter>
</activity>
 For more complex data passing, please read
the tutorial
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A Design Template: Provider
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Intent intent = getIntent(); // why am I called
String action = intent.getAction();
Uri data = intent.getdata();
String hotelName = data.getPath();
// do the booking
setResult(RESULT_OK);
finish();
}
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