Android Application Development at JFokus 2011

Android Application
Development
JFokus 2011

Anders Göransson

tisdag den 15 februari 2011

About You

• Android experience

• None / Little

• Moderate / Experienced


Agenda
Android
Android Application UI
intro
User
Experience
Broadcast
Service Content
Receiver
Provider Intents

Application
Design

Android
Android External Market
Fragmentation Tools

Android History

• 2005 - Google acquires Android Inc.

• 2007 Sep - Mobile patents ﬁled

• 2007 Nov - Open Handset Alliance

• 2008 Sep - Android 1.0

• 2008 Oct - G1 (HTC Dream)


2011 - Why Develop for Android?



I. Market share. The future is Android!



II. Android will be everywhere!



III. It’s open source, it’s free and it’s powerful



IV. It’s Java!


Android Platform


Android Platform

Linux Process

• Each process holds Virtual Machine

• Application runs in a sandbox

• Applications run with distinct system identity

• User Id

• Isolated from other applications and platform

• Android contains an RPC mechanism for IPC


Android Platform

Linux Process
Default behavior
App A

Process A

System starts
App A


Android Platform

Linux Process
Default behavior
App A

Process A

System starts System starts
App A App B
App B

Process B


Android Platform

Linux Process
Conﬁgured behavior
App A

Process A

System starts
App A


Android Platform

Linux Process
App A App A
App B
Process A

App A App B


Android Platform

Linux Process
Conﬁgured behavior - Same Process name
- Same User Id
- Same signing cert
App A App A
App B
Process A

App A App B


Android Platform

Linux Process
App A App A

Process A

System starts App starts
App A components


Android Platform

Linux Process
App A App A App A

Process A

System starts App starts App starts
App A components component

Process B


Android Platform

Linux Process
App A App A App A

Process A

IPC
App A components component

Process B


Android Platform

Android and Java
• Apache Harmony class libraries

• Java 5.0

• Dalvik Virtual Machine

• Memory optimizations

• One VM per application

• .class-ﬁles -> .dex-ﬁles

• 2.2/Froyo+ includes Just In Time-compilation

• Register based (not stack based)


Android Platform

Building

.java .class .dex

.jar .apk


Android and Java

Runtime
.dex
App Resources
Manifest
apk


Android and Java

Runtime
.dex
App Resources
Manifest
apk
Optimized
Dalvik VM Environment


Android and Java

Runtime
.dex
App Resources
Manifest
apk
Optimized
Dalvik VM Environment

Linux properties
Linux process
- Process Id
- User Id
- Thread model


Android Application
Application

Activity
AndroidManifest.xml
“Manifest”
Activity

Broadcast Content
Service
Receiver Provider
Resources


Android Application
Application App
descriptor

Activity UI
AndroidManifest.xml
“Manifest”
Event Data
Activity
Background
listener provider
tasks Media
XML
...

Broadcast Content
Service
Receiver Provider
Resources


Android Application
Application App
descriptor

Activity UI
AndroidManifest.xml
“Manifest”
Event Data
Activity
Background
listener provider
tasks Media
XML
...

Broadcast Content
Service
Receiver Provider
Resources

= Component


Android Application

Minimum
Application

Activity AndroidManifest.xml

Plain UI application
Resources


Android Application

AndroidManifest.xml
<manifest>

<uses-permission />
<permission />
Security

<uses-sdk />

Constraints
<uses-configuration />
AndroidManifest.xml
<uses-feature />
<supports-screens />
Activity
<application>

<activity>...</activity>

<service>...</service>

<receiver>...</receiver>
Components
<provider>...</provider>

</application>

</manifest>


Android Application

Application

• Base class for global application state <manifest>
<application>
AndroidManifest.xml
Activity
• Subclass to deﬁne behavior <activity>
<service>
<receiver>
• Accessible from all components <provider>
</application>

• Started before all components </manifest>

Start
onCreate()

Active
onTerminate()

Finish


Android Application

Application

•
Notified when device configuration changes while the
application is running
AndroidManifest.xml
Activity
• Device configuration

• Keyboard open/closed (HW + HW/SW)

• User changes global setting

• Locale, Font, etc.

• Orientation change

• MCC/MNC change


Android Application

Resources

• Multimedia files
• Images
AndroidManifest.xml

• XML -files
Activity

• Layouts
• Animations
• Values (strings, dimensions, colors)
• Menu-definitions
• Preferences

Android Application Resources

Resource definitions
/res

/anim /fade_in.xml

AndroidManifest.xml
/drawable
Activity

/layout

/values

/xml

/raw


/res

/anim Bitmaps: *.png, *.jpg

Nine-patches: *.9.png
AndroidManifest.xml
/drawable Shapes: Descriptive drawings commands, *.xml
Activity
Layers: Multiple drawables compound to one,
*.xml
/layout
States: Select one drawable in a list based on
state, e.g. Button, *.xml
/values
Levels: Select one drawable in a list based on
level, e.g. Battery level, *.xml
/xml

/raw


/res

/anim

AndroidManifest.xml
/drawable
Activity

/layout /layout_myactivity.xml

/values

/xml

/raw


/res

/anim <?xml version="1.0" encoding="utf-8"?>
<resources>
<string name="app_name">SpotifySearcher</string>
<string name="artist">Artist</string>
<string name="search">Search</string>

AndroidManifest.xml <string name="search_result">Search result:</string>

/drawable
</resources>

Activity

/layout
/strings.xml
/colors.xml
/values /dimens.xml
/arrays.xml
/xml

/raw


/res

/anim

AndroidManifest.xml
/drawable
Activity

/layout

/values

/preferences.xml
/xml
/*.xml

/raw


/res

/anim

AndroidManifest.xml
/drawable
Activity

/layout

/values

/xml

/raw Arbitrary ﬁles


Providing Resources
/res
public final class R {
public static final class attr {
}
public static final class color {

/anim public static final int dark_grey=0x7f040001;
public static final int white=0x7f040000;
}
public static final class dimen {
public static final int margin_vertical_default=0x7f050001;
AndroidManifest.xml public static final int padding_default=0x7f050000;

/drawable public static final int text_size_default=0x7f050002;
public static final int text_size_large=0x7f050003;

Activity }

Pre-compile
public static final class drawable {
public static final int icon=0x7f020000;
}
public static final class id {
/layout public static final int button_search=0x7f070001;
public static final int edit_search_input=0x7f070000;
public static final int text_search_result=0x7f070002;
}
public static final class layout {
public static final int activity_search=0x7f030000;

/values }
public static final int divider_line=0x7f030001;

public static final class string {
public static final int app_name=0x7f060000;
public static final int artist=0x7f060001;
public static final int search=0x7f060002;

/xml
public static final int search_result=0x7f060003;
}
}

/raw


Providing Resources
/res
public final class R { R.java
public static final class attr {
}
public static final class color {

/anim public static final int dark_grey=0x7f040001;
}
public static final class dimen {
public static final int margin_vertical_default=0x7f050001;
AndroidManifest.xml public static final int padding_default=0x7f050000;

/drawable public static final int text_size_default=0x7f050002;

Activity }

Pre-compile
public static final class drawable {
public static final int icon=0x7f020000;
}
public static final class id {
/layout public static final int button_search=0x7f070001;
}

/values }


/xml
}
}

/raw

UI
• Programmatic and Descriptive UI

• Declare UI in XML description
• Manipulate UI programmatically
AndroidManifest.xml

• Separate UI presentation from UI behavior
Activity

Java
object
<Element>
<Element>
<Element> Inﬂate Java Java
<Element> object object
<Element>

Java Java
object object


UI

AndroidManifest.xml

Activity

View
Group
<ViewGroup>
<View>
<ViewGroup> Inﬂate Java View
<View>
object Group
<View>

Java Java
object object


UI

AndroidManifest.xml

Activity

View
Group
<ViewGroup>
<View>
<ViewGroup> Inﬂate View
View
<View>
Group
<View>

View View


UI

Layouts

• Implements ViewGroup

• Common layouts
AndroidManifest.xml
•
Activity
LinearLayout

• RelativeLayout

• TableLayout


UI

Layouts

• Implements ViewGroup

• Common layouts
AndroidManifest.xml
•
Activity
LinearLayout

• RelativeLayout

• TableLayout

Consider
Inﬂating objects is expensive. Use as
few elements as possible.

Use ‘layoutopt’

UI

Layout Example
<?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"
android:padding="@dimen/padding_default">
<EditText
android:id="@+id/edit_search_input"
AndroidManifest.xml android:layout_height="wrap_content"
android:hint="@string/artist" />
<Button

Activity android:id="@+id/button_search"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="@dimen/margin_vertical_default"
android:layout_marginTop="@dimen/margin_vertical_default"
android:text="@string/search" />
<include
layout="@layout/divider_line" />
<TextView
Linear android:layout_height="wrap_content"

Layout android:layout_marginTop="@dimen/margin_vertical_default"
android:textSize="@dimen/text_size_default"
android:text="@string/search_result"/>
<TextView
android:id="@+id/text_search_result"
android:background="@color/dark_grey"
android:textSize="@dimen/text_size_large"/>
Text Text </LinearLayout>
EditText Button
View View


UI

Drawing UI
• Top-down traversal

• Measure

• ﬁll_parent, wrap_content, “ﬁx value”
AndroidManifest.xml
•
ActivityLayout

• layout_*
Linear
Layout

Text Text
EditText Button
View View


UI

Use Resource Separation
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
<EditText
AndroidManifest.xml
<Button
android:id="@+id/button_search"

Activity
<include
<TextView
<TextView
</LinearLayout>


UI

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

<color name="white">#ffffff</color>
<color name="dark_grey">#222222</color>
android:layout_width="fill_parent" </resources>
<EditText
AndroidManifest.xml
<Button
android:id="@+id/button_search"

Activity
<include
<TextView
<TextView
</LinearLayout>


UI


<EditText
<resources>
<dimen name="padding_default">20dp</dimen>
AndroidManifest.xml
<Button
android:id="@+id/button_search" dimens.xml <dimen name="margin_vertical_default">20dp</dimen>

Activity
<dimen name="text_size_default">15sp</dimen>
<dimen name="text_size_large">20sp</dimen>
</resources>
<include
<TextView
<TextView
</LinearLayout>


UI


<EditText
<resources>
<dimen name="padding_default">20dp</dimen>
AndroidManifest.xml
<Button
android:id="@+id/button_search" dimens.xml <dimen name="margin_vertical_default">20dp</dimen>

Activity
<dimen name="text_size_default">15sp</dimen>
<dimen name="text_size_large">20sp</dimen>
</resources>
<include
<TextView <?xml version="1.0" encoding="utf-8"?>
android:layout_width="fill_parent" <resources>
android:layout_height="wrap_content" <string name="app_name">SpotifySearcher</string>
strings.xml <string name="artist">Artist</string>
<string name="search">Search</string>
android:text="@string/search_result"/> <string name="search_result">Search result:</string>
<TextView </resources>
</LinearLayout>


UI

Activity

• Application component Activity
• Subclassed by application

• User interface

• Typically one full size screen

• Inﬂates UI layouts

• Key events

• Activity initialization

• onCreate()


UI

Accessing Resources
public class ActivitySearch extends Activity {

private EditText editSearch;
Activity
private TextView textSearchResult;
private Button buttonSearch;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_search);

editSearch = (EditText) findViewById(R.id.edit_search_input);
AndroidManifest.xml
buttonSearch = (Button) findViewById(R.id.button_search);
textSearchResult = (TextView) findViewById(R.id.text_search_result);
}
Activity

1. Inﬂate layout
2. Access by Id


UI

Accessing Resources
public class ActivitySearch extends Activity { public final class R { R.java

private EditText editSearch;
Activity public static final class attr {
}
private TextView textSearchResult; public static final class color {
private Button buttonSearch; public static final int dark_grey=0x7f040001;
/** Called when the activity is first created. */ }
@Override public static final class dimen {
public void onCreate(Bundle savedInstanceState) { public static final int margin_vertical_default=0x7f050001;
super.onCreate(savedInstanceState); public static final int padding_default=0x7f050000;
setContentView(R.layout.activity_search); public static final int text_size_default=0x7f050002;
editSearch = (EditText) findViewById(R.id.edit_search_input); }
AndroidManifest.xml
buttonSearch = (Button) findViewById(R.id.button_search); public static final class drawable {
textSearchResult = (TextView) findViewById(R.id.text_search_result); public static final int icon=0x7f020000;
} }
Activity public static final class id {
public static final int button_search=0x7f070001;
}

1. Inﬂate layout }

2. Access by Id
}
}


UI

Lists

• Commonly used

• Needs to be efﬁcient

• Not consume too much memory

• Fast scrolling

• Android-way of handling lists efﬁciently


UI Lists

The problem
Data source List
Data 1 UI Element
Data 2
...

Problem Requirement
Arbitrary data source Abstract mechanism
Arbitrary data type Look and feel of each element
Dynamic data Update list after insert, edit, remove
Lots of data requires a lot of memory Effective caching

UI Lists

API
Data source
Data 1
Data 2
...

Problem Requirement

UI Lists

API
Data source
Data 1
Data 2
... <interface>
Adapter

Problem Requirement

UI Lists

API
Data source
Data 1
Data 2
... <interface>
... Adapter

Problem Requirement

UI Lists

API
Data source
Data 1
Data 2
... <interface>
... Adapter
list_item_layout.xml

Problem Requirement

UI Lists

API
Data source
Data 1 list_item_layout.xml
Data 2
... <interface>
... Adapter ... list_item_layout.xml


Problem Requirement

UI Lists

API
AdapterView
Data source
Data 2
... <interface>


Problem Requirement

UI Lists

API
list_layout.xml
AdapterView
Data source
Data 2
... <interface>


Problem Requirement

UI Lists

Adapter
<interface>
Adapter

BaseAdapter

Cursor ArrayAdapter
SimpleAdapter
Adapter

SimpleCursor
Adapter


User Experience

• Critical for application success

• UX

• UI design

• Employ a good designer

• Deliver expected behavior

• Master the Activity lifecycle

• Responsive

• Master the thread handling


User Experience Activity

Lifecycle
States

Active Foreground

Partly
Paused
obscured

Completely
Stopped
obscured



Lifecycle
States

Active Foreground

Partly
Paused
obscured
Active

Completely
Stopped
obscured
Activity stack



Lifecycle
States

Active Foreground

Paused
Partly Active
obscured
Stopped

Completely
Stopped
obscured
Activity stack



Lifecycle
States

Active Foreground

Active

Paused
Partly Paused
obscured
Stopped

Completely
Stopped
obscured
Activity stack



Lifecycle
Start

Active

Paused

Stopped

Finish


Lifecycle
Start

• System callbacks

Active • Override in subclass

Paused

Stopped

Finish


Lifecycle
Start

onCreate()

onStart()

onResume() • System callbacks


Paused

Stopped

Finish


Lifecycle
Start

onCreate()

onStart()



onPause()

Paused

Stopped

Finish


Lifecycle
Start

onCreate()

onStart()



onPause()

Paused
onStop()

Stopped

Finish


Lifecycle
Start

onCreate()

onStart()



onPause()

Paused
onStop()

Stopped
onDestroy()

Finish


Lifecycle
Start

onCreate()

onStart() onRestart()



onPause()

Paused
onStop()

Stopped
onDestroy()

Finish


Lifecycle
Start

onCreate()

Entire lifetime
onResume()
- Long lived objects
- Create UI
Active
onPause()

Paused
onStop()

Stopped
onDestroy()

Finish


Lifecycle
Start

onCreate()

Visible lifetime
onResume()
- Visible but possibly not in
foreground
Active
onPause()

Paused
onStop()

Stopped
onDestroy()

Finish


Lifecycle
Start

onCreate()

Foreground lifetime
onResume()
- User interaction
- Frequent cycle
Active
- Example: Device screen sleep
onPause() mode
- Lightweight code
Paused
onStop()

Stopped
onDestroy()

Finish


Activity transition
Tip
Activity 1 Save state in onPause()

Active

onPause()

I Active

onStop()
Activity stack
Stopped


Activity transition
Tip
Activity 1 Activity 1I Save state in onPause()

Active Start

onPause()
onCreate()
onStart()
II Active
onResume()
I Stopped
Active
onStop()
Activity stack
Stopped


Activity transition
Tip
Activity 1 Activity 1I Save state in onPause()

Active Start

Execution path
onPause()
onCreate()
onStart()
II Active
onResume()
I Stopped
Active
onStop()
Activity stack
Stopped


Lifecycle Extras
Start

onCreate()

onPostCreate()
onResume()
onPostResume()
Active
onPause()

Paused
onStop()

Stopped
onDestroy()

Finish


Lifecycle Extras
Start

onCreate()

onPostCreate()
onResume()
onPostResume()
Active
onPause()
System methods.
Paused
Normally not used by
application.
onStop()

Stopped
onDestroy()

Finish


Lifecycle changes

• The User navigates away from the Activity

• To another Activity

• onStop(), onDestroy() if ﬁnish() is called

• BACK-button (Donʼt override unless well motivated)

• onDestroy()

• HOME-button

• onStop()

• Other App in front, e.g. incoming call, onStop()

• Screensaver

• onPause()



Task


User Experience

System Cleanup

• System can shut down a process at any time due to low
available resources

• The processes are ranked according to importance

• Foreground process

• Visible process

• Service process

• Background process

• Empty process


User Experience System Cleanup

Process Hierarchy
- Activity in the foreground (onResume called)
- Service executing platform callback (onCreate, onStartCommand, onDestroy)
Foreground
- BroadcastReceiver executing platform callback



Process Hierarchy
Foreground

- Visible Activity (onPause)
- Hosts Service bound to by visible Activity
Visible



Process Hierarchy
Foreground

Visible

- Explicitly started Service (startService)
Service



Process Hierarchy
Foreground

Visible

Service

- Background Activity (onStop)
Background



Process Hierarchy
Foreground

Visible

Service

- Background Activity (onStop)
Background

- No active components
Empty



Process Hierarchy
Foreground

Visible

Service

- Background Activity (onStop) Tip!
Background
Long running tasks in Activity or
BroadcastReceiver are best handled in a
- No active components Service instead of local Thread. The
Empty
process is then ranked higher and the
risk of interruption is decreased.


Background Process
Problem
Foreground

MyActivity
Some text



Background Process
Problem
Foreground Background

MyActivity MyActivity
Other
Some text Activity

OtherActivity
starts



Background Process
Problem
Killed
Other Other
Activity Activity
Some text

OtherActivity System shuts down
starts MyActivity



Background Process
Problem
Killed Foreground

Other Other MyActivity
Activity Activity
Some text

OtherActivity System shuts down User presses
starts MyActivity “Back”



Background Process
Solution
• Activity.onSaveInstanceState(Bundle)

• Called when Activity is destroyed by the system

• Not a lifecycle method

• Data that should be retrieved is set in a Bundle

• put*-methods



Background Process
Solution
Killed
Other Other
Activity Activity
Some text

starts MyActivity



Background Process
Solution
Killed
Other Other
Activity Activity
Some text

starts MyActivity

@Override
protected void onSaveInstanceState(Bundle bundle) {
super.onSaveInstanceState(outState);
bundle.putString(key, “Some Text”);
}



Background Process
Solution
Killed Foreground

Activity Activity
Some text Some text


@Override
}



Background Process
Solution
Killed Foreground

Activity Activity
Some text Some text


@Override
@Override
protected void onCreate(Bundle bundle) {
super.onCreate(bundle);
String str = bundle.getString(key);
...
}
}


User Experience

Master the thread model

• Each application runs in one Linux process by default

• Single-threaded model - Main / UI thread

• All components and system calls run in the UI thread.

• Blocking the UI thread blocks all components

• UI toolkit not thread-safe

• All UI operations must be made on the UI thread


User Experience Master the thread model

Application Not Responding



Thread Model

Process A



Thread Model

App A

Process A

System starts
App A



Thread Model

App A App A

Process A UI thread

System starts App starts
App A components



Thread Model

App A App A App A

Process A UI thread UI thread

...
Worker threads

App A components worker threads



Thread Model
- Blocks the UI thread
- Use only lightweight tasks
- All UI manipulations !
App A App A App A


...
Worker threads




Thread Model
- Blocks the UI thread
- Use only lightweight tasks
- All UI manipulations !
App A App A App A


...
Worker threads

- Time consuming tasks
- No UI manipulations
!


Thread Handler API

1. Activity.runOnUiThread(Runnable)
2. View.post(Runnable)
3. Handler public class MyActivity extends Activity {

private TextView textView;

private void startLongRunningOperation() {

new Thread(new Runnable() {
public void run() {
results = doSomethingExpensive();
runOnUiThread(new Runnable() {
public void run() {
textView.setText(results);
}
});
}
}).start();
}



Thread Handler API

3. Handler


new Thread(new Runnable() {
public void run() {
textView.post(new Runnable() {
public void run() {
}
});
}
}).start();
}



Thread Handler API

public class MyActivity extends Activity {

3. Handler // Need handler for callbacks to the UI thread
final Handler handler = new Handler();

// Create runnable for posting

final Runnable updateResults = new Runnable() {

public void run() {

// UPDATE UI WITH “results”
}
};


//Fire off a thread to do some work that we shouldn't do
//directly in the UI thread
Thread t = new Thread() {
public void run() {
handler.post(updateResults);
}
};
t.start();
}


Android Application Development at JFokus 2011

Android Application Development at JFokus 2011

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