Android Component Model

7/31/2019 Android Component Model

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Android Application ModelComponent Model for Mobile Applications

Dominik Gruntz

University of Applied Sciences Northwestern Switzerland, Brugg-Windisch8925



2

IntroductionAndroid Experience> Android Core Libraries (together with Noser)

> Android Projects – HikeTracker [swisstopo] – SyncML Addressbook Synchronizer

[Swisscom]

Component Software Experience> Responsible for the Java

Chapter of the Book on

"Component Software"



3

AGENDAAndroid Components> Activities

– Intents & Filters – Task / Application – Lifecycle

– Processes and Threads> Services> Content Providers



4

Android Software Stack> Java

> C/C++

> Kernel



5

Android ComponentsActivity [User Interaction]> UI component typically corresponding to a screen

– E.g. Contacts: 3 activities: View contacts, Send message, Edit contactService [Service Provider]> Background process without UI (e.g. mp3 player)

– Messages can be sent from and to a serviceContent Provider [Data Provider]> Enables applications to share data

– E.g. Contacts are provided to all applicationsBroadcast Receiver [System Event Listener]> Responds to external events, can wake up your process

– Phone rings, network activity established, time controlled



6

ActivityActivity is usually a single screen> Implemented as a single class extending Activity

> Displays user interface controls (views)> Reacts on user input / events

An application typically consists of

several activities> Each screen is typically 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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IntentsIntent> Intents are used to move from activity to activity

> Intent describes what the application wants to do> Consists of

– Action to be performed (MAIN / VIEW / EDIT / PICK / DELETE / …) – Categories

– Data to act on (URI) – Extras (primitives / primitives[] / Strings / Serializable) – Flags Intent intent = new Intent(Intent.ACTION_VIEW);

intent.setData(Uri.parse("http://www.fhnw.ch"));

Intent intent = new Intent(Intent.ACTION_EDIT);intent.setData(Uri.parse("content://contacts/people/1"));



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IntentsIntent Invocation> Launch new activity (without receiving a result)

> Launch new activity and expect result

– When activity exits, onActivityResult method is called with givenrequestCode (int > 0)onActivityResult(int requestCode, int resultCode, Intent result)

startActivity(intent);

startActivityForResult(intent, requestCode)



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IntentsIntent Specification> Intents define the interface between components

> Intent repository on www.openintents.org



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Intents and Intent FiltersIntent Filters> Description of what intents an activity can handle

> Activities publish their intent filters in a manifest file

> Upon invocation of startActivity(intent) thesystem looks at the intent filters of allinstalled applications

<intent-filter android:priority="0"><action android:name="android.intent.action.VIEW"/><category android:name="android.intent.category.DEFAULT"/><category android:name="android.intent.category.BROWSABLE"/><data android:scheme="geo"/>

</intent-filter>



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Android Component ModelComponent Software> Activities can reuse functionality from other

components simply by making a requestin form of an Intent

> Activities can be replaced at any timeby a new Activity with an equivalentIntent Filter

Intent i = new Intent("com.google.android.radar.SHOW_RADAR");

i.putExtra("latitude", 47.6f);i.putExtra("longitude", 8.23f);startActivity(i);



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Android Component ModelAndroid Market: Software Libraries> Radar

> HighScore List> Text-To-Speech Library> Log Collector

– Includes standalone app



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Android Component ModelPackaging: APK File (Android Package)> Collection of components

> Components share a set of resources – Preferences, Database, File space

> Components share a Linux process – By default, one process per APK

> APKs are isolated – Communication via Intents or AIDL

> Every component has a managed lifecycle

APK

Process

Activity Activity

Content Provider

Service



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Task / Application / ProcessTask (what users know as applications)> Collection of related activities

> Capable of spanning multiple processes> Associated with its own UI history stack

APK

Process

Activity Activity

Content Provider

Service

APK

Process

Activity Activity

Content Provider

Service



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Task / Application / ProcessTasks> Processes are started & stopped as needed

> Processes may be killed to reclaim resources> Upon Invocation of another activity, the view state can be saved

> Comparable with EJB's stateful session beans (SFSB)> Each Android component has a managed lifecycle

Home Inbox Details Browse MapsInbox Details



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Activity Life CycleActive / Running> Activity is in foreground

> Activity has focus

Paused> Still visible, partially overlaid

> Focus lost

Stopped> Activity is not visible

Destroyed> Activity was terminated or killed

New

Running

PausedStopped

Destroyed

onCreate()onStart()[onRestoreInstanceState()]

onResume()onSaveInstanceState()onPause()

onRestart()onStart()onResume()

onStop()

onDestroy()

<<kill>>

<<kill>>

onResume()

onPause()onStop()onDestroy()



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Activity Life Cycle (1/2)onCreate> Called when activity is first created (with null parameter)

or when activity was killed (called with a bundle)> Initialization of viewsonRestart> Called when activity was stopped only

onStart> Activity becomes visible to user, animations could be startedonRestoreInstanceState> Restore view state

onResume> New activity is visible, TOS, camera might be used here



18

Activity Life Cycle (2/2)onSaveInstanceState> Save UI state of a complex dialog

=> onCreate=> onRestoreInstanceState

> If application is explicitly finished, this method is not called> Called before or after onPauseonPause> Activity no longer TOS but still visible> New activity is not started until onPause returnsonStop

> Activity no longer visibleonDestroy> Release resources; it is not guaranteed that this method is called



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Activity Life Cycle Samples (1/2)Open Child Activity> onCreate(null) -> onStart -> onResume() -> [Open Child Activity]

> onSaveInstanceState() -> onPause() -> onStop() -> [Close Child Activity]> onRestart() -> onStart() -> onResume()Transparent View> onCreate(null) -> onStart -> onResume() -> [Open Transparent View]

> onSaveInstanceState() -> onPause() -> [Close Transparent View]> onResume()Turn Display> onCreate(null) -> onStart -> onResume() -> [Turn Display]> onSaveInstanceState() -> onPause() -> onStop() -> onDestroy()

-> onCreate() -> onStart() -> onRestoreInstanceState() -> onResume()



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Activity Life Cycle Samples (2/2)Home> onCreate(null) -> onStart -> onResume() -> [Home Button]

> onSaveInstanceState() -> onPause() -> onStop() -> [Start App]> onRestart() -> onStart() -> onResume()Phone Call Interrupt> onCreate(null) -> onStart -> onResume() -> [Phone Call]

> onSaveInstanceState() -> onPause() -> onStop() -> [Hang Up or press Back]> onRestart() -> onStart() -> onResume()



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Process / Thread

Threading Overview> Each process has one thread (by default)

=> Single Threaded ModelThreads and Loopers> Each thread has a Looper to handle a message queue> Events from all components are interleaved into the looper/Queue

APK Process Thread Looper

MessageQueueHandler

1 1 11

1

1

1*



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Process / Thread

ActivityThread> Manages the main thread in an application process

> Calls Looper.loop

Looper.loop

while(true){

Message m=queue.next();// may blockif(m!=null){

m.target.dispatch- Message(m);

m.recycle();}

}

APK

Process

Activity

Activity

IntentRecvr

Thread

Looper

Message

Queue

LocalService Calls

UI Events

System Events



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Process / Thread

Location Update in HikeTracker (onLocationChanged)



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Process / Thread

Activity Result call-back (onActivityResult)



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Process / Thread

Inactive Activities> If an activity does not consume events,

the system assumes that the activityhas a problem> AndroidNotResponding is shown

– No reaction to UI event within 5Sec

– No reaction to BroadcastEvent within 10Sec



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Dealing with Threads

checkRoot

> Compares current threadwith thread which createdthe view

button.setOnClickListener(new OnClickListener() {@Override

public void onClick(View v) {new Thread() {

@Override public void run() {

input1.setText("" + counter1++);}

}.start();}

});



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Dealing with Threads

Activity.runOnUiThread(Runnable)> Runs the specified action on the UI thread, i.e. the action is posted into the event

queue of the UI thread

Handler> Associated with a thread and its message queue

> Used to add messages in the message queue – sendMessage postRunnable – sendMessageAtFrontOfQueue postAtFrontOfQueue – sendMessageAtTime postAtTime

– sendMessageDelayed postDelayed> Used to handle the request (called by associated thread)



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Android Process & Security

Security Model> Each application runs in its own process

– Has its own unique Linux User ID – Each application has access to its own data

> Other resources are only available by defined interfaces – Services [exposes functionality] – Content Provider [exposes data]

USER PID PPID VSIZE RSS WCHAN PC NAMEroot 23 1 69508 18668 c008be9c afe0b874 S zygoteradio 87 23 100940 16320 ffffffff afe0c824 S com.android.phone

app_2 92 23 101792 17900 ffffffff afe0c824 S android.process.acoreapp_14 120 23 93772 11444 ffffffff afe0c824 S com.google.process.gappsapp_8 158 23 100088 11860 ffffffff afe0c824 S com.android.mmsapp_21 160 23 99740 13064 ffffffff afe0c824 S ch.fhnw.imvs.helloapp_0 175 23 90580 11116 ffffffff afe0c824 S com.android.alarmclockapp_3 183 23 94784 12080 ffffffff afe0c824 S android.process.media



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Android Processes

public class P1/P2 extends Activity {...

public void onStart(){super.onStart();Properties p = System.getProperties();System.out.println("getProperties().id = " +

System.identityHashCode(p));System.out.println("getProperties().size() = " + p.size());

if(p.get("Android") == null){ p.put("Android", 0); }else { p.put("Android", ((Integer)p.get("Android"))+1); }

System.out.println("P1/2: onStart " + p.get("Android"));

System.out.println("getProperties().size() = " + p.size());}

}



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Processes: Output

Output of Activity P1

Output of Activity P2

INFO/System.out(12470): getProperties().id = 1073834816

INFO/System.out(12470): getProperties().size() = 37INFO/System.out(12470): P1: onStart 0INFO/System.out(12470): getProperties().size() = 38

INFO/System.out(12504): getProperties().id = 1073834816INFO/System.out(12504): getProperties().size() = 37INFO/System.out(12504): P2: onStart 0INFO/System.out(12504): getProperties().size() = 38



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Android Processes

Zygote> Upon startup Zygote process is created which partially initializes a VM instance

– Core system libraries dex-files are loaded (mmap) – Dalvik VM is initialized and shared heap (which contains

objects used by all processes) is created> Upon start of an activity the Zygote process is forked

– Application specific dex files are loaded (mmap) – Application specific heap (and VM structures)

are initialized=> Core system libraries are shared! Zygote

SystemLibraries

Home

APKCode

Maps

APKCode



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Service

Characteristics> Execution of long running tasks and business logic outside an activity

– E.g. a background task that has to download data periodically> Services can explicitly be started and stopped> Communication with service

– In-process if service runs in same APK

– Inter-Process Communication across APKs (AIDL)



33

Service

Explicit control> startService(intent)

– onCreate -> onStart> stopService(intent)

– onDestroy

Implicit control> bindService(intent, conn, flags)

– onCreate -> onBind> unbindService(conn)

– onUnbind



34

Service Inter Process Communication

Binder> Bridges Kernel and Process space

> Proxy and Stub classes are generated from AIDL definitions

AIDL data types> Primitive types, String, CharSequence

> List, Map> AIDL generated interfaces> Parcelable classes

AIDL extensions> in, out, inout on parametres> oneway for asynchronous invocations



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Service Sample: AIDL Interface

interface ICounterService {long getCurrentValue();void setCounterListener(in ICounterListener l);

}

interface ICounterListener {void valueChanged(long value);

}

ICounterService

ICounterService.Stub

Binder

ICounterService.Stub.Proxy

CounterBinder

IBinder



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Service Sample: Manifest

<?xml version="1.0" encoding="utf-8"?><manifest xmlns:android="http://schemas.android.com/apk/res/android"

package="ch.fhnw.imvs.counter"

android:versionCode="1" android:versionName="1.0">

<application><service android:name=".CounterService" >

<intent-filter><action

android:name="ch.fhnw.imvs.counter.ICounterService"/></intent-filter>

</service></application>

</manifest>



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Service Sample: Invocation

Bind Service

Unbind Service

Intent start = new Intent("ch.fhnw.imvs.counter.ICounterService");

conn = new ServiceConnection() { public void onServiceConnected(ComponentName name, IBinder b) {ICounterService service = ICounterService.Stub.asInterface(b);service.setCounterListener(new ICounterListener.Stub() {

public void valueChanged(final long value) { … }});

}});

bindService(start, conn, Context.BIND_AUTO_CREATE);

unbindService(donn);



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Content Provider

Content Provider> The only way to share data between Android Packages

> Implements a standard set of methods to provide access to data> Any form of storage can be used

– SQLite DB – Files

– Remote Store

APK

Process

Activity Activity

Content Provider

APK

Process

Activity



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Content Provider

Content Provider Interface

abstract class ContentProvider { public Cursor query (Uri uri, String[] projection,

String selection, String[] selectionArgs,String sortOrder);

public Uri insert (Uri uri, ContentValues values) public int delete (Uri uri, String selection,

String[] selectionArgs);

String getType (Uri uri);

public int update (ContentURI uri,

ContentValues values, String selection,String[] selectionArgs)}



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Content Provider

Access to Data Providers> Comparable to a DB Access (Cursor)

> Identification via URI – content://contacts/phones

String[] projections = new String[]{"number", "name", "_id", "photo"};

Cursor cur = managedQuery(new ContentURI("content://contacts/phones"),

projections, null, "name ASC");



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Content Provider Sample

public class Provider extends android.content.ContentProvider { public static final android.net.Uri CONTENT_URI =

Uri.parse("content://ch.fhnw.imvs.fibonacci/numbers");

public static final String ID = BaseColumns._ID; public static final String VALUE = "value";

public boolean onCreate() { return true; }

public Cursor query(Uri uri, String[] projection,String selection, String[] selectionArgs, String sortOrder){

MatrixCursor c =new MatrixCursor(new String[]{ID,VALUE},10);for(int i=0; i<10; i++)

c.addRow(new Object[]{i, getNumber(i)});return c;

}



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Content Provider Sample Client

private void listFibonacciNumbers(){String[] projection = new String[]{BaseColumns._ID, "value"};Cursor cur = this.managedQuery(

Uri.parse("content://ch.fhnw.imvs.fibonacci/numbers"), projection, null, null, null);

cur.moveToFirst();do {

log.append(String.format("fib(%s) = %s",cur.getString(0), cur.getString(1)));

log.append("/n");} while (cur.moveToNext());

}



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Android Application Model: Summary

Scalability> Model well suited for mobile devices

– Optimized memory usage – Linux-based Security Model

Component Model

> Interesting programming model> Existing activities may be reused / extended



Dominik GruntzUniversity of Applied Sciences [email protected]

Steinackerstrasse 55210 Windisch / Switzerland

Android Component Model

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