android training deck

7/12/2019 Android Training Deck

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Introduction to

Android ApplicationDevelopment

Friday, December 17, 2010



Goals for the week

• Introduce Android architecture and SDK

• Get hands-on experience with tools

• Create a few demo apps, and gain skills and

knowledge to develop your own




Android devices

Wide range of:

•Manufacturers

•Providers

•Screen sizes

•Screen densities

•Keyboards

•Network capabilities

•Tablets and phonesFriday, December 17, 2010



Android Technology




A software stack for mobile devices

Includes:

•Operating system•Middleware

•Key applications

•SDK for writing apps




Android Architecture




Built-in applications

• Mail client

•Messaging (SMS) program

• Calendar and contacts

• Maps

• Web browser

• Others (depending on distribution)




Application framework

• Open development platform

•Design encourages component re-use

• Includes:

• Views (controls)

•Content providers

• Resource manager

• Activity manager

• Notification manager




Core Libraries

• System C library (libc)

•Media Libraries

• Surface manager

• LibWebCore

• SGL (2D graphics engine)

•3D libraries (OpenGL ES)

• FreeType

• SQLite




Android runtime

• Core libraries with most of Java’s librarycapability

• Dalvik VM: Executes Dalvik bytecode

• Each app runs in its own process




Dal-what?

• Dalvik VM != JVM

•Dalvik VM is optimized for smartphone

hardware

• VM is register-based, not stack-based

•Runs its own bytecode: Dalvik Executable

(.dex) format; minimal memory footprint

• Utility converts Java bytecode into .dex




Linux kernel

• Linux 2.6 kernel

• Security, memory management, process

management, networking

•Abstraction layer between hardware and

rest of software stack




ApplicationFundamentals




Each app lives in its own world

• Each app runs in its own Linux process

• Each process has its own Dalvik virtualmachine

•Each app is assigned a unique Linux user ID

• Files are visible only to that one application




Application components

and re-use• Individual components of one app can be

used by another, if permission is given

• App 1 can launch a component of App 2,

giving the appearance of embedding

•Apps have no single entry point; built

instead as individual components




Activities

• A UI for one focused task for the user

•Examples:• Choose an item from a catalog

• Compose a text message

• Choose somebody to send a message to

•Each app has one or more activities

• They work together, but each is independent

• One activity usually starts the next




ActivitiesChoose a hotel Describe the hotel Choose a room




Activities

• Each is given a default window to draw in

•Usually fills the screen

• Can create other windows (like a dialog or

pop-up)

• Can create new full-screen views within thesame activity




Activity stack

• Activity A calls startActivity()

• Activity B starts and covers the screen

• User presses hardware Back button

• Activity B finishes, exposing Activity A




Activity stack




Launching an activity from

Home

Text




Difference between

HOME and BACK




Activity lifecycle events

Activities have three main states:

• active

• paused• stopped




Activity lifecycle




Intents

•Asynchronous messages that:

• launch an activity,

• launch a service,

• or notify a broadcast receiver.




Example: View a web

page

Action and data




Intent object

• Component name

• Action

• Data (URL)

• Category

• Extras

• Flags

A bundle of information passed in

an intent, optionally containing:




Explicit intents

Often used to start one activity from

another within the same application.

Component name

Extra data

Context reference




Implicit intents

No specific application or activity is named.

Usually for activating components in other apps.

Android uses intent filters to figure out which

activity to launch, according to action, data,

and category .

Apps declare intent filters for each activity in

the manifest.




Choosing an activity for an

intent




Two ways to start an

activity

• startActivity(intent);

•No result returned from child

• startActivityForResult(intent, requestCode);• Child returns a result (as int and another intent)

• Child calls setResult(int)

• Caller implements onActivityResult() to get the result




Application manifestAndroidManifest.xml

Names the application ID(package)

Lists theactivities, and

their attributes

Sets otheroptional

parameters

Declares requiredpermissions




Activities and tasks

Task: what the user experiences as a single “application”

A group of activities, managed as a stack.

Normally, activites are only pushed/poppped, never

re-arranged.

The entire stack (task) goes foreground/

background as a unit.




Flags and attributes affect

stack and task behavior

• Activities normally belong to the same task

• FLAG_ACTIVITY_NEW_TASK: System

puts the new activity in a different task




What happens to a task in

the background?• Normally, system clears all activities except

the root activity if it’s been in the

background “a long time”.

• Boolean attributes to control this:

•alwaysRetainTaskState (root activity)

• clearTaskOnLaunch (root activity)

• finishOnTaskLaunch




Three ways to shut down

an activity

this.finish();

this.finishActivity(int requestCode);

User presses BACK key




Returning to the root

activity




Ending a task

The root activity finishes, either by the

user pressing BACK or the activity

calling finish() on itself.

Android itself manages the lifetime of the application!




Refresher on Java

conce ts

• Nested classes

• Anonymous inner classes




Nested classes

• Logically group classes that are used only in one

place.• Increase encapsulation.

• Can make code more readable and maintainable.

• Static vs non-static




Anonymous inner classes

public class OuterClass { public void startThread1() { Runnable mRunnable = new Runnable() { @Override

public void run() { // do something here

} };

Thread t = new Thread(mRunnable); t.start();

};

public void startThread2() { Thread t = new Thread(new Runnable() {

@Override public void run() { // do something here

} });

t.start(); };

}




Access to local variables




Lab: Hello, Negotiator!(in three parts)




Application resources




main.xml

strings.xml




Application resources

Two different devices, both using default resources:

Two different devices, one using alternative resources:

Resources should always be externalized.




Organizing resources

Source and resource folder structure

Precompiler




Specifying alternative

resourcesResource folder naming convention




View and ViewGroup

All UIs are built with a combination of

Views and ViewGroups.




Control views (Widgets)

• Button

• TextView

• EditText

• CheckBox

• ImageView

• ListView

• RadioButton

• Spinner

• ...your own custom View




Creating a custom View

Extend View directly, or extend an existing Widget:

In the XML layout, use the full class name of

your custom view:




UI event listeners

Each interface has one callback method:


http://developer.android.com/reference/android/view/View.OnCreateContextMenuListener.html

http://developer.android.com/reference/android/view/View.OnCreateContextMenuListener.html

http://developer.android.com/reference/android/view/View.OnTouchListener.html

http://developer.android.com/reference/android/view/View.OnTouchListener.html

http://developer.android.com/reference/android/view/View.OnKeyListener.html

http://developer.android.com/reference/android/view/View.OnKeyListener.html

http://developer.android.com/reference/android/view/View.OnFocusChangeListener.html

http://developer.android.com/reference/android/view/View.OnFocusChangeListener.html

http://developer.android.com/reference/android/view/View.OnLongClickListener.html

http://developer.android.com/reference/android/view/View.OnLongClickListener.html

http://developer.android.com/reference/android/view/View.OnClickListener.html

http://developer.android.com/reference/android/view/View.OnClickListener.html



Implementing an event listener

In your Activity class:





// Create an anonymous implementation of OnClickListener

private OnClickListener mCorkyListener = new OnClickListener() { public void onClick(View v) {

// do something when the button is clicked }

};

protected void onCreate(Bundle savedValues) { ... // Capture our button from layout Button button = (Button)findViewById(R.id.corky);

// Register the onClick listener with the implementation above button.setOnClickListener( mCorkyListener); ...

}

As an anonymous class, and a field:





As an anonymous class, directly:

protected void onCreate(Bundle savedValues) {

... // Capture our button from layout Button button = (Button)findViewById(R.id.corky); // Register the onClick listener with the implementation above button.setOnClickListener(new OnClickListener() { public void onClick(View v) { // do something when the button is clicked }

}); ...

}




Event handler return values

Some have no return value (void)

Others return a boolean indicating whether

the event was (should be) consumed.




Layouts


L t iti hild t l



Layouts position child controlsfor the UI.

Major layout classes:

•FrameLayout

•LinearLayout

•RelativeLayout

•TableLayout

Layouts can re-size and re-position controls to

give a good presentation on different screen sizes

and orientations.


D fi l h XML



Define layouts either in XMLor in Java code.




Common View attributes


Parent view group defines which



Parent view group defines whichlayout parameters are available

for each child .




Units of measure

• Pixels (px)

• Density-independent pixels (dip or dp)• Based on 160 dpi; 160 dp is always one inch

• Scale-indepent pixels (sp)• Like dp, but scaled by font-size preference

• Points (pt)

• 1/72 of an inch

• Millimeters (mm)

• Inches (in)




References in value strings

• Literal value

• Reference to a resource in our own package

• Reference to a resource in another package

android:padding="50dp"

android:background="#888888"

android:background="@drawable/myImage"

android:background="@color/blue"

android:background="@android:drawable/someDrawable"




id

Generate a new ID value called someNewId and assign it to this item.

Use an existing ID (in our own resources).

Use an existing ID (in the standard Android namespace).




layout_height and layout_width

Set the height of this item to match the height of its parent.

Make this item just high enough to enclose its content.

Set the height of this item to exactly 42 device-independent pixels.


layout margin and padding



layout_margin and padding

Leave 24dp of space all around the edges of this item when

laying it out, if possible.

Leave 24dp of space at the top edge of this item when laying it

out, if possible.

Leave 24dp of all around the contents of this item, if possible.


it d l t it



gravity and layout_gravity

android:gravity=

Center the content of this item within the item horizontally.

Center the content of this item within the item, both vertically

and horizontally.

Center this item within its parent, both vertically and horizontally.


background



background

Set this item’s background to a solid white color.

Set this item’s background to transparent (alpha = 00).

Set this item’s background to a color named pricelineDarkBlue,

which is defined in an XML resource file.

Set this item’s background to a Drawable called mySpecialBackground,

which might be a bitmap image or an XML-defined shape.




frameLayout


LinearLayout



LinearLayout

Stacks child views in a vertical or horizontal line.

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:layout_width="fill_parent"

android:layout_height="fill_parent"

android:orientation="vertical" android:gravity="center"

android:background="@color/pricelineDarkBlue"> <Button android:text="Larry"

android:layout_width="wrap_content" android:layout_height="wrap_content"/>

<Button android:text="Curly" android:layout_width="wrap_content"

android:layout_height="wrap_content"/> <Button android:text="Moe"

android:layout_width="wrap_content" android:layout_height="wrap_content"/>

</LinearLayout>


Li L i f l



LinearLayout is usefuland flexible.

• Horizontal and vertical LinearLayouts can

be nested to create complex layouts.

• Wrap several controls in a LinearLayout to

align or format them as a group.

•Pay close attention to gravity and

layout_gravity attributes.


T bl L



TableLayout


RelativeLayout



RelativeLayout


L ft d i ht li t ith



Left- and right-alignment withRelativeLayout

<RelativeLayout

xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent"

android:layout_height="fill_parent"

android:background="@color/pricelineDarkBlue">

<Button android:text="Larry" android:id="@+id/larry"

android:layout_alignParentLeft="true" android:layout_width="wrap_content"

android:layout_height="wrap_content"/> <Button android:text="Curly"

android:layout_toRightOf="@id/larry" android:layout_width="wrap_content"

android:layout_height="wrap_content"/> <Button android:text="Moe"

android:layout_alignParentRight="true" android:layout_width="wrap_content"

android:layout_height="wrap_content"/></RelativeLayout>


S llVi



ScrollView




Optimizing layouts

• Avoid unnecessary nesting

• Avoid using too many views (not more than80!)

• Avoid deep nesting (fewer than 10 levels!)

• Run the layoutopt utility on your layoutsto get recommendations for optimization


I fl l



Inflating a layout




Includes

One layout can include another.




View stubs: lazy includes


Adding to a layout at



Adding to a layout at

runtime




Context

Context: Interface to global information

about an application environment

Base class of Activity, Service, and Application

getString()

getResources()getApplicationInfo()

getTheme()etc.




Lab: ZipLookupPart One


M



Menus


Expanded menus



Expanded menus


C t t



Context menu


D fi i



Defining a menu

Create an XML in the /res/menu directory.


U i i h i i



Using a menu in the activity

Inflate the

menu XML

Handle the

selection event


ListView



ListView




ListView and ListAdapter

ListView shows the list; the data comes from

ListAdapter.




Standard adapters

ArrayAdapter<T>

BaseAdapter

SimpleAdapter

CursorAdapter

These all implement Adapter




Using ArrayAdapter

For each item, populates a single

TextView with the value returnedby toString().

Data is defined as an array of objects.




Extending ArrayAdapter


Using SimpleAdapter



Using SimpleAdapter

Data is a defined as a List of Maps.Rows can have more than one field.


Extending BaseAdapter



Extending BaseAdapter


O h f Ad



Other uses of Adapter

Gallery, ListView, and Spinner all

extend AdapterView

Gallery: Horizontally-scrolling list locked at the center

Spinner: Drop-down list of items, like a combo box




Lab: Navigator


N ifi i



Notifications

• Toast Notification

Brief pop-up message from the background

• Status Bar Notification

Persistent reminder from the background thatrequests a response

• Dialog Notification

Pop-up, modal message from the activity


T



Toast


T



Toast


C



Custom toast view


S b ifi i



Status bar notifications

Status bar icons

Icon with ticker message

Notifications window

(pull down the status bar)

Some are Ongoing.


Creating a notification



Creating a notification

String ns = Context.NOTIFICATION_SERVICE;

NotificationManager mNotificationManager = (NotificationManager)

getSystemService(ns);

int icon = R.drawable.notification_icon;

CharSequence tickerText = "Hello";

long when = System .currentTimeMillis();

Notification notification = new Notification(icon, tickerText,

when);

Context context = getApplicationContext();

CharSequence contentTitle = "My notification";

CharSequence contentText = "Hello World!";

Intent notificationIntent = new Intent(this, MyClass.class);

PendingIntent contentIntent = PendingIntent.getActivity(this, 0,

notificationIntent, 0);

notification.setLatestEventInfo(context, contentTitle,

contentText, contentIntent);

private static final int HELLO_ID = 1;

mNotificationManager.notify(HELLO_ID, notification);

Get notification manager ref

Instantiate notification

Define expanded message,intent

Pass to NotificationManager


O h ifi i f



Other notification features

• Update existing notification

•Custom expanded viewLayout takes the place of standard title and text

• Add sound

•Add vibration

• Add flashing lights


Di l



Dialogs

• AlertDialog

•ProgressDialog

• DatePickerDialog

• TimePickerDialog

Create a dialog from within onCreateDialog(int).


C ti di l



Creating dialogs

static final int DIALOG_PAUSED_ID = 0; static final int DIALOG_GAMEOVER_ID = 1;

protected Dialog onCreateDialog(int id) {

Dialog dialog; switch (id) {

case DIALOG_PAUSED_ID: // do the work to define the pause Dialog

break; case DIALOG_GAMEOVER_ID:

// do the work to define the game-over Dialog break;

default: // unknown dialog

dialog = null; }

return dialog;} public void showPausedDialog() {

showDialog(DIALOG_PAUSED_ID); }


C ti Al tDi l



Creating an AlertDialog


Al t di l ith li t



Alert dialog with list


Si l di l



Simple progress dialog




Lab: Hello, NegotiatorWho Cannot Be

Ignored!

(Parts 1 and 2)


St l d Th



Styles and Themes

Same idea as cascading style sheets (CSS)

Instead of this:

You can do this:


Defining styles



Defining styles

Styles can inherit from other styles.

Some styles are built-in. (@android:style/*)

Custom styles go in one or more <resources> xml.


Style inheritance



Style inheritance

Inherit from your own styles using dot-notation.


Style vs theme



Style vs. theme

In layout.xml, style appliesto a specific View, only.

In <activity> tag inmanifest.xml, style appliesto all views in the activity.

In <application> tag inmanifest.xml, style appliesto all views in the entire

application.


Some built in themes



Some built-in themes

You can use these directly, or extend them.

Theme

Theme.NoTitleBarTheme.NoTitleBar.Fullscreen

Theme.Light

Theme.Black

Theme.TranslucentTheme.Dialog

Theme.Dialog.Alert


Dialog themes



Dialog themes

res/values/styles.xml:




Lab: Hello, NegotiatorWho Cannot Be

Ignored!

(Part 3)




Drawables


Drawable



Drawable

• BitmapDrawable

• ShapeDrawable

• PictureDrawable

• LayerDrawable

• etc.

Something that can be drawn.


Three ways to create a



Drawable

• Image saved in project resources

• XML file that defines Drawable properties

• In code, using class constructors


Using image resources



Using image resources

Id is image filename, without the extension

Acceptable characters: [a-z0-9_.]


Two ways to load from



code

or, as Drawable:

as ImageView:


Creating from resource XML



Creating from resource XML

Can be used for any Drawable

subclass that supports inflate().

Example: ShapeDrawable from Negotiator app:


Using a ShapeDrawable in a



custom View


NinePatch Drawable



NinePatch Drawable

Stretchable bitmap image that resizes itself cleanly.

Example: Backgrounds of standard Android buttons

Standard PNG image with extra 1-pixel border lines

Save with .9 extension in res/drawable


Caution: Each resource has



only one stateResources res = getResources();

Drawable myImage1 = res.getDrawable(R.drawable.my_image);

Drawable myImage2 = res.getDrawable(R.drawable.my_image); // The following line changes the alpha for both myImage1 and myImage2.

myImage1.setAlpha(128);


Solution: mutate() method



Solution: mutate() method

Resources res = getResources();

Drawable myImage1 = res.getDrawable(R.drawable.my_image);

Drawable myImage2 = res.getDrawable(R.drawable.my_image); // The following line changes the alpha for only myImage1.

myImage1.mutate().setAlpha(128);


Selector drawable



Selector drawable

This could be used as the background of a button:


Color state list

http://schemas.android.com/apk/res/android

http://schemas.android.com/apk/res/android



Color state list




Animation


Animation types



Animation types

• Frame animation: Rapid sequence of pre-

created frames that give the illusion of motion

• Tween animation: Series of transformations

on a View object, defined as start and end


Frame animation



Frame animationBased on AnimationDrawable class

XML file goes in res/drawable:


Frame animation



Frame animation


When to call start()



When to call start()

• Don’t call in onCreate();

AnimationDrawable isn’t fully attached tothe window yet

• Consider onWindowFocusChanged() for

animation that starts immediately


Negotiator opening screen



Negotiator opening screen


Tween animation



Tween animation

• Gradually change certain properties of a

View object

• Alpha, scale, translate, rotate

• Specify, either in code or XML:

•Start and end states

• Total time

• Interpolation curve


Sample animation resource



<set android:interpolator="@android:anim/decelerate_interpolator"> <scale android:fromXScale="1.4"

android:toXScale="0.0" android:fromYScale="0.6" android:toYScale="0.0"

android:pivotX="50%"

android:pivotY="50%"

android:startOffset="700" android:duration="400"

android:fillBefore="false" /> <rotate

android:fromDegrees="0"

android:toDegrees="-45" android:toYScale="0.0"

android:pivotX="50%"

android:pivotY="50%" android:startOffset="700" android:duration="400" />

</set>


Applying an animation



Applying an animation

or


Interpolators



p

Define the rate of change of an animation.

AccelerateInterpolator

AccelerateDecelerateInterpolator

LinearInterpolator

BounceInterpolatorOvershootInterpolator


Animation timing



Animation timing

• A set of animations can be sequential orsimultaneous

• Simultaneous: Animations have same start

times

•Sequential: Time the second one to begin

after the first one ends


Sequential animations



Sequential animations

<set android:interpolator="@android:anim/linear_interpolator"> <scale android:fromXScale="1.4"

android:toXScale="0.0" android:fromYScale="0.6" android:toYScale="0.0" android:startOffset="0" android:duration="500" /> <rotate

android:fromDegrees="0"

android:toDegrees="-45" android:toYScale="0.0"

android:startOffset="500" android:duration="500" />

</set>




Lab: ZipLookupPart Two (Animation)




Concurrency


Threading Practices



g

• Don’t block the main thread

•Perform all UI operations on main thread!

• Put long-running, non-network tasks in the

background

• Consider using asynchronous pattern formost I/O


Threads in Android



• Use standard Java Thread objects (and

Runnable interfaces)

• Convenience classes for managing threads• Example: Handler for processing messages on the main

thread


What’s wrong with this?



g

public void onClick(View v) {

Bitmap b = loadImageFromNetwork();

mImageView.setImageBitmap(b);

}


OK, how about this?



,

public void onClick(View v) {

new Thread(new Runnable() {

public void run() {

Bitmap b = loadImageFromNetwork();

mImageView.setImageBitmap(b);

}

}).start();

}


Access the UI thread from



a background thread

• Activity.runOnUiThread(Runnable)

• View.post(runnable)

• View.postDelayed(Runnable, long)

• Handler


This is one solution



This is one solution


Use AsyncTask



y


Sample HTTP client



p

Don’t run this on the main thread;

plug it into AsyncTask instead.


Compatibility acrossA d id i

http://www.priceline.com/

http://www.priceline.com/



Android versions


Android API levels



API levels also have

nicknames like Cupcake and

Gingerbread.

Use Build.VERSION.SDK_INT

to detect API level at

runtime.


API levels in the manifest



minSdkVersion

Minimum API Level required for the app to run.

targetSdkVersion

API Level on which the app is designed to run.

maxSdkVersion

Maximum API Level on which the app is able to run.(Deprecated .)


Platform version



Compile against the lowest possible version

that your app can support.


Using features in newer



Android versions• Check runtime platform using Build class

• Use Java reflection to load new classesand/or execute new methods

• Suggestion: Put reflection code in a

separate class


Reflection example



p


Designing for performance



g g p

Device has:

•Limited computing power

• Limited storage

• Limited battery life

Even if app runs fast enough, consider power!


Optimization tips



p p

• Write good, well-structured and well-

layered code to begin with.

• Avoid design decisions that will limitperformance -- things that will be hard to

change later.

• Don’t guess; measure performance beforeand after optimization.


Specific tips



p p

• Avoid creating objects!

• Re-use objects within a loop

• Avoid creating short-term temporaryobjects

• Prefer static over virtual (15%-20% faster)

• Avoid internal getters and setters (3x-7x

slower than direct field access)


Design for responsiveness



• An app can be fast, yet still

be unresponsive

• ANR dialog if app can’trespond to user input within

5 seconds

• The main (UI) thread isprecious -- protect it!




Location Services


android.location package



• Get instance of LocationManager system

service

•Query for list of all installed

LocationProviders

• Register/unregister for periodic updates

from a given provider

• Register/unregister for a given Intent to fire

when we get close to something


Location awarenesschallenges



challenges

• Several different location sources, all

returning different data

• The user might be moving

• For each provider, accuracy varies over

time


Requesting updates from aspecific provider



specific provider

Call requestLocationUpdates() once for

each provider of interest.Friday, December 17, 2010

Typical application flow




Quick fix: last knownlocation



location

Returns a cached location instantly --

but it might be old!


Power-saving tips



• Reduce the size of the update window

• Set the updates to return less frequently

• Use only the Network provider, rather than

the GPS provider




Using abd, DDMS andLogCat


adb: Android Debug Bridge



Client-server program in 3 pieces:

• Command-line client (adb)

• Server: background process on the PC

• Daemon: background process on the

emulator or device

3 pieces communicate over TCP sockets.


Sample adb commands



• adb devices

• adb install something.apk

• adb uninstall appid

• adb push <local> <remote>

• adb pull <remote> <local>

• adb logcat


Remote adb shell




DDMS: Dalvik DebugMonitor Server



Monitor Server

• Uses adb path to connect to device

• Can connect via TCP to debug port of anyrunning VM

• Functions as “router” to connect Eclipse

debugger to selected VM


Starting DDMS



From Eclipse:

Switch to DDMS perspective

From command line:


DDMS standalone




Eclipse DDMS perspective




Sample DDMS features



• LogCat (in a window)

•Threads and allocations

• File explorer

• Screen capture

• Force a GC




Profiling ApplicationPerformance


Execution trace files



Generate a trace file

Copy to development machine

adb pull /sdcard/calc.trace .


Analyze a trace file



traceview calc

Timeline panel:


Profile panel



Services


Service



• An application component that doesn’t

have a user interface

• Runs on the main thread of the app, in thebackground, indefinitely

• Activities can bind to the service, start it,

stop it, and exchange data with it

• Can interact directly with other apps


What a Service isn’t:



• A separate application or process

• A way to run things in a separate thread


Service lifecycle




Service lifecycle methods



•void onCreate()

• void onStart(Intent intent)

• void onDestroy()


Other Service callbacks



• IBinder onBind(Intent intent)

•boolean onUnbind(Intent intent)

• void onRebind(Intent intent)

IBinder: Communications channel used by clients tointeract with the service


Binding to a service



• Clients call Context.bindService()

• Creates the service if not already running

• Returns an IBinder object

• Service remains running at least until all clients

disconnect


Service permissions



• Manifest contains a <service> tag

• Service can declare its own, home-made<permission> item in this tag

• If so, any app that wants to connect needs

a matching <uses-permission> tag


Simple example: Service runningin same process as its clients



p


Simple example (continued)




Client that uses service




Remote client bindingoptions



p

• Use AIDL

• Complete interface definition that you define

in an .aidl file

• Tools will generate stub and proxy classes

• Use Messenger class

• Connects to a local Handler to exchange

messages across processes


Service syntax in manifest



On the same level as <activity> declarations:




Content providers


Store and retrieve dataacross applications



across applications

• Android doesn’t support direct sharing of

files

• Some content providers are built in, likeimage library, address book, settings,

browser bookmarks

• Apps can expose their own contentproviders for other apps to consume


Two choices for publishing



data

1. Create your own content provider, or

2. Add data to an existing content provider, if

it supports the same kind of content and

you have permission to write to it.


Common interface forcontent providers



p

Android system figures out the appropriate

content provider to match the query, and

makes sure it’s up and running.

Query is expressed as a URI.


Content provider URIs



Each provider exposes a URI that uniquely identifies

its data set -- or one for each data set it supports.

Each ContentResolver method takes the URI

as its first argument.


How data is exposed



Simple table model.

_ID field uniquely identifies record within the table,

and can be used to match data in other tables.


Query returns a Cursor



Actual URL: content://contacts/people/23


Format of a content:// URI



A: Standard prefix (always content://)

B: Authority

C: Path used by CP to determine type of databeing requested

D: ID of a specific record (optional)


Other query arguments• Names of columns to return



• Names of columns to return

• WHERE clause (filtering rows)

• Selection arguments

• ORDER BY clause (sorting rows)


Reading from the cursor




Reading large binary data



Data for some columns might be returned as a

content: URI String, rather than an object.


Modifying data - addingrecords




Change values for existingrecords




Creating your own contentprovider



• Set up some way to store the data (e.g.,

SQLite database)

• Extend ContentProvider class to access it

• Declare the ContentProvider class in your

manifest


Extending ContentProvider



Create CONTENT_URI

Define column names as public static String values,including “_id”

Implement methods:


Declare the content providerin the manifest



Sensors


Android Device Sensors



• Accelerometer

•Compass

• Proximity

• Ambient Light

• Gyroscope (Nexus S)


Even more Sensors...




Enumerating availablesensors



A device can have more than one sensor of a given type.


Available sensors



HTC Nexus One:

Motorola Droid:


Accelerometer



Measures acceleration,not velocity .


Accelerometer applications




Useful (and useless)acceleration constants



SensorManager.GRAVITY_EARTH

SensorManager.GRAVITY_JUPITER

SensorManager.GRAVITY_DEATH_STAR_I


Listening for changes




Isolating or ignoring gravity

Use a low -pass filter if you’re only interested in the



orientation of the device.Use a high-pass filter if you’re only interested in

sudden motions.


Magnetic Field sensor



• Senses orientation of a magnetic field

• Measures field strength in x, y, z axes,similar to Accelerometer

• Most common application: Electronic

compass


Electronic compass

+y



-y

+x-x

N

y

x

α

α = arctan(y/x)

α = 45°

So we mustbe facing

Northwest.

y/x = 1.0


Orientation



• Actually a combination of acceleration and

magnetic field sensors

• Takes into account device orientation

• Easy way to access Compass information

• Returns azimuth, pitch, and roll


Gyroscope



Measures rate of rotation around each axis.

These values are usuallyintegrated over time to

produce an angle.


Don’t forget to shut off!



• Registered sensor listeners will keep

getting updates as long as app is running

• Doesn’t matter if screen is locked, activity

is paused or destroyed

•Un-register to prevent draining the battery




Lab: ApiDemos




Activities: Managing state


A paused activity could bedestroyed at any time.



• If your Activity is sensitive to state, save the

state in the onPause() method, and restoreit in onCreate().

• Or, override onSaveInstanceState().


Using shared preferences




ImplementingonSaveInstanceState()



• System will call onSaveInstanceState() just

before the activity is destroyed.

• Default implementation callsonSaveInstanceState() on all the subviews.

• When the activity is re-started, onCreate()

will be called with a non-NULL Bundle, and

so will onRestoreInstanceState().


What’s a Bundle?Name-value pairs that can be serialized.



Values can be primitives, Strings, arrays,

Parcelables, and other bundles.


Special case: Configurationchange



• onRetainNonConfigurationInstance()

• getLastNonConfigurationInstance()


Testing Activity statemanagement




Application-level state



• Create a subclass of the Application class,and name it in your manifest

• Store application-wide values in your

Application-derived class

• Values are retained as long as app remains

alive, even if Activities are destroyed


Editing shared preferences




/res/xml/options.xml




Activity that managesreferences



Search


Search is a core feature



• Anything is searchable, even if the data isn’t

on the device

•Seamless and consistent search experience

across the whole system

• Android search framework has two parts:

•User interface for kicking off a search

• Interaction layer that communicates withinstalled apps


Local search



Current

activity isn’t

interruptedwhen the

search box

appears.


SearchManager handles it



• SearchManager shows the search dialog

when the Search key is pressed

• SearchManager creates an Intent thatpasses the search query to your designated

search-handler Activity

•Your search-handler Activity performs the

search and presents the results


Create a searchableconfiguration



res/xml/searchable.xml

The android:hint might be “Search MyApplication”


Create a searchable Activity

M d h ACTION SEARCH i



Must respond to the ACTION_SEARCH intent.

Must point to the searchable.xml resource.


Decide which Activities shouldenable the Search button.



A searchable context is any Activity for which you have

declared searchable meta-data in the manifest file.

Or, enable the

entire app:


Implementing the search-handler Activity



Receive and process the query:

Best way to return the results: an Adapter.


Present the results



•Typically, using a ListView; you would

extend your Activity from ListActivity.

• Results can be presented any way you like.


If the search-handler activityis the current activity...



Mark the activity android:launchMode="singleTop"


Adding custom suggestions

You can suggest results that match the

l tt t d f



letters entered so far.

These can also be shownin the system-wide Quick

Search Box!


Custom suggestion steps



• Implement a basic search-handler Activity

• Create a Content Provider to supply data

• Modify searchable configuration with info

about your content provider

• Declare the Intent to be sent when user

selects a suggestion


After Search box isdisplayed:



• Search Manager puts text-so-far into a Query

and sends it to your content provider

• Your CP returns a Cursor with all matching

results

•SM displays the list of suggestions from your

Cursor.


Modify the searchableconfiguration



res/xml/searchable.xml


Handling the suggestion query



content://your.authority/optional.suggest.path/SUGGEST_URI_PATH_QUERY/sometext

SearchManager calls your query() method with

a URI that looks like this:

String query = uri.getLastPathSegment().toLowerCase();

Get the query text:


Returning the result Cursor



Android expects certain specific columns

to be returned in your Cursor object.

See the Android documentation for the

full specification.

Examples: First line of text, second line of text, icon


Declare the Intent action

Determines the Intent when the user



Normally, it is ACTION_VIEW.

Determines the Intent when the userchooses a suggestion.


Handling the Intent in yoursearch-handler Activity




Expose suggestions to theQuick Search Box



AndroidManifest.xml:

res/xml/searchable.xml:




Multimedia


MediaPlayer: Multimediaplayback



• Initialize the Media Player, with media to

play

• Prepare the Player for playback

• Start playback

• Stop (or pause)


MediaPlayer state machine




Simple audio playback

From Negotiator app:



Playing a system sound:


Asynchronous prepare




Playback errors



• Various reasons why playback can fail:• Unsupported media type or encoding

•Resolution too high

• Streaming I/O errors

• Set up an OnErrorListener handler

• Catch IllegalStateException and

IllegalArgumentException


Video playback



• Video needs a Surface to be displayed upon

• VideoView control has a built-in Surface,and encapsulates MediaPlayer

• Or, create and use a SurfaceView object


VideoView control



Lab: Audio and Video


Further Reading



• Android Developer

Documentation: docs/

index.html

• Android 2 ApplicationDevelopment

•Pro Android 2




Enjoy Android!

android training deck

Documents