Download Android Application Model

Android Application Model
Component Model for Mobile Applications
Dominik Gruntz
University of Applied Sciences Northwestern Switzerland, Brugg-Windisch
8925
2
Introduction
Android 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
AGENDA
Android Components
> Activities
– Intents & Filters
– Task / Application
– Lifecycle
– Processes and Threads
> Services
> Content Providers
4
Android Software Stack
> Java
> C/C++
> Kernel
5
Android Components
Activity
[User Interaction]
> UI component typically corresponding to a screen
– E.g. Contacts: 3 activities: View contacts, Send message, Edit contact
Service
[Service Provider]
> Background process without UI (e.g. mp3 player)
– Messages can be sent from and to a service
[Data Provider]
Content Provider
> Enables applications to share data
– E.g. Contacts are provided to all applications
[System Event Listener]
Broadcast Receiver
> Responds to external events, can wake up your process
– Phone rings, network activity established, time controlled
6
Activity
Activity 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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Intents
Intent
> 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"));
8
Intents
Intent Invocation
> Launch new activity (without receiving a result)
startActivity(intent);
> Launch new activity and expect result
startActivityForResult(intent, requestCode)
–
When activity exits, onActivityResult method is called with given
requestCode (int > 0)
onActivityResult(int requestCode, int resultCode, Intent result)
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Intents
Intent Specification
> Intents define the interface between components
> Intent repository on www.openintents.org
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Intents and Intent Filters
Intent Filters
> Description of what intents an activity can handle
> Activities publish their intent filters in a manifest file
<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>
> Upon invocation of startActivity(intent) the
system looks at the intent filters of all
installed applications
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Android Component Model
Component Software
> Activities can reuse functionality from other
components simply by making a request
in form of an Intent
> Activities can be replaced at any time
by a new Activity with an equivalent
Intent Filter
Intent i = new Intent(
"com.google.android.radar.SHOW_RADAR");
i.putExtra("latitude", 47.6f);
i.putExtra("longitude", 8.23f);
startActivity(i);
12
Android Component Model
Android Market: Software Libraries
> Radar
> HighScore List
> Text-To-Speech Library
> Log Collector
– Includes standalone app
13
Android Component Model
Packaging: 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 / Process
Task (what users know as applications)
> Collection of related activities
> Capable of spanning multiple processes
> Associated with its own UI history stack
Process
Activity
Activity
Process
Activity
Activity
APK
APK
Content Provider
Content Provider
Service
Service
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Task / Application / Process
Tasks
> Processes are started & stopped as needed
> Processes may be killed to reclaim resources
> Upon Invocation of another activity, the view state can be saved
Home
Inbox
Details
Browse
> Comparable with EJB's stateful session beans (SFSB)
> Each Android component has a managed lifecycle
Maps
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Activity Life Cycle
New
Active / Running
> Activity is in foreground
> Activity has focus
Paused
> Still visible, partially overlaid
> Focus lost
onRestart()
onStart()
onResume()
onCreate()
onStart()
[onRestoreInstanceState()]
onResume()
Running
onResume()
onStop()
Paused
Stopped
Stopped
> Activity is not visible
Destroyed
> Activity was terminated or killed
onSaveInstanceState()
onPause()
onDestroy()
onPause()
onStop()
onDestroy()
<<kill>>
Destroyed
<<kill>>
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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 views
onRestart
> Called when activity was stopped only
onStart
> Activity becomes visible to user, animations could be started
onRestoreInstanceState
> 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 onPause
onPause
> Activity no longer TOS but still visible
> New activity is not started until onPause returns
onStop
> Activity no longer visible
onDestroy
> Release resources; it is not guaranteed that this method is called
19
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()
20
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 Model
Threads and Loopers
> Each thread has a Looper to handle a message queue
> Events from all components are interleaved into the looper/Queue
APK
1
Process
1
1
Thread
1
Looper
1
1
Handler
*
1
Message
Queue
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Process / Thread
ActivityThread
> Manages the main thread in an application process
> Calls Looper.loop
APK
Looper.loop
while(true){
Message m=queue.next();
// may block
if(m!=null){
m.target.dispatchMessage(m);
m.recycle();
}
}
Process
Activity
Thread
Local
Service Calls
Looper
Activity
Intent
Recvr
UI Events
Message
Queue
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 activity
has 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
button.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
new Thread() {
@Override
public void run() {
input1.setText("" + counter1++);
}
}.start();
}
});
checkRoot
> Compares current thread
with thread which created
the view
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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)
28
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
USER
root
radio
app_2
app_14
app_8
app_21
app_0
app_3
PID
23
87
92
120
158
160
175
183
PPID
1
23
23
23
23
23
23
23
VSIZE RSS
WCHAN
PC
69508 18668 c008be9c afe0b874
100940 16320 ffffffff afe0c824
101792 17900 ffffffff afe0c824
93772 11444 ffffffff afe0c824
100088 11860 ffffffff afe0c824
99740 13064 ffffffff afe0c824
90580 11116 ffffffff afe0c824
94784 12080 ffffffff afe0c824
NAME
S zygote
S com.android.phone
S android.process.acore
S com.google.process.gapps
S com.android.mms
S ch.fhnw.imvs.hello
S com.android.alarmclock
S android.process.media
> Other resources are only available by defined interfaces
– Services
[exposes functionality]
– Content Provider
[exposes data]
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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
INFO/System.out(12470):
INFO/System.out(12470):
INFO/System.out(12470):
INFO/System.out(12470):
getProperties().id
= 1073834816
getProperties().size() = 37
P1: onStart 0
getProperties().size() = 38
Output of Activity P2
INFO/System.out(12504):
INFO/System.out(12504):
INFO/System.out(12504):
INFO/System.out(12504):
getProperties().id
= 1073834816
getProperties().size() = 37
P2: onStart 0
getProperties().size() = 38
31
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
Home
objects used by all processes) is created
APK
> Upon start of an activity the Zygote process is forked
Code
– Application specific dex files are loaded (mmap)
– Application specific heap (and VM structures)
are initialized
Maps
=> Core system libraries are shared!
Zygote
APK
Code
System
Libraries
32
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
> oneway
on parametres
for asynchronous invocations
35
Service Sample: AIDL Interface
interface ICounterService {
long getCurrentValue();
void setCounterListener(in ICounterListener l);
}
interface ICounterListener {
void valueChanged(long value);
}
IBinder
Binder
ICounterService
ICounterService.Stub
CounterBinder
ICounterService.Stub.Proxy
36
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>
37
Service Sample: Invocation
Bind 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);
Unbind Service
unbindService(donn);
38
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
APK
– SQLite DB
Process
– Files
APK
Activity
Activity
– Remote Store
Process
Activity
Content Provider
39
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)
}
40
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");
41
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;
}
42
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());
}
43
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 Gruntz
University of Applied Sciences
Steinackerstrasse 5
5210 Windisch / Switzerland
[email protected]