Android Development- the basics

Tomáš Kypta@TomasKypta

Outline

● Android platform● Android ecosystem● Android SDK and development tools● Hello World● building blocks & the manifest file● activities, widgets, intents● dialog, toasts, notifications● fragments

Android platform

● Linux-based operating system● open-source● originally phone OS● tablet (since Honeycomb, Android 3.0)● Google TV● hundreds of devices

History

● 2003, Android inc.● 2005 acquired by Google● Sep 2008 first Android phone – T-Mobile G1● since then rapid development of the platform● May 2010 Froyo● Feb 2011 Honeycomb● Oct 2011 Ice Cream Sandwich● Jul 2012 Jelly Bean

Android ecosystem

● the world's most popular mobile platform● 1.3M new devices activated every day● of that 70k tablets● total number of devices ~ 500 million

● play.google.com (market.android.com)● other store – Amazon Appstore for Android, ...

Google Play

● ~ 675 000 apps in the market● total downloads > 25 billion● ~ 70% free apps● ads, in-app billing● selling – 15 min return period● buy – ČR, SR● sell – ČR● Google Play contains also music, books

– not available in ČR, SR

Android problems

● fragmentation● manufacturer/carrier enhancements● updates & support● openness – low quality apps in Google Play● malware - users

Permissions

● users accept when installing or updating the app

● apps can be installed directly from .apk file

Sources

● developer.android.com● android-developers.blogspot.com● source.android.com● stackoverflow.com● youtube.com/androiddevelopers● svetandroida.cz

Development

● programming in “Java”● native apps possible (C++)

● development tools platform friendly● Windows, Linux, Mac OS X● IDE support – ADT plugin for Eclipse,

Netbeans, IntelliJ IDEA, ...● you can freely develop on your device

Android SDK● android – Android SDK and AVD Manager● adb – Android Debug Bridge● ddms – Dalvik Debug Monitor● emulator● lint, hierarchyviewer, Traceview● ProGuard● docs, samples

Libraries

● compatibility libraries

– v4 – backports lots of newer functionality to android 1.6+

● licensing, billing libraries

● AdMob● Google Analytics, Flurry, Crittercism, ...● C2DM

Android internals

Hello World

Build

Android Building Blocks

● Activity● Service● Content provider● Broadcast receiver

● AndroidManifest.xml

Activity

● screen with user interface● the only visual component

● example – an email app can contain:– list of emails

– email detail

– email composition

– preference screen

– ...

Service

● has no UI● long-running tasks

● examples:– music playback service

– download service

– sync service

Content Provider

● manages and shares application data● data storage doesn't matter – database, web,

filesystem● apps can query and modify data through

content provider● read/write permissions can be defined● examples:

– all system databases

– contacts

– SMS

Broadcast Receiver

● responds to broadcasts● broadcasts are system wide● can be registered statically or dynamically● system or custom messages● examples:

– incoming SMS, incoming call

– screen turned off

– low baterry

– removed SD card

AndroidManifest.xml

● defines what parts the app have● defines which endpoints are exposed● minimum/maximum API level● permissions● declare hardware and software features● required configuration

Intent

● asynchronous message● binds components together (all of them

except ContentProvider)● starting activities● starting services and binding to services● sending broadcasts

Activity

● a subclass of android.app.Activity● app usually has many activities● activities managed in activity stack

– newly started activity is place on the top of the stack

Activity Lifecycle

● activity can be in different states during it's lifecycle:

– foreground

– visible

– stopped

– killed

● when activity state changes a system callback is called

Activity callbacks

● onCreate() - activity created● onStart() - becoming visible to the user● onResume() - gains user focus● onPause() - system resuming previous

activity● onStop() - becoming invisible to the user● onDestroy() - before activity destroyed● onRestart() - if it was previously stopped,

prior to onStart()

Intent & Activity

● starting activity explicitly

● starting activity implicitly

● starting activity for result

Configuration changes

● when configuration changes activities are destroyed and recreated by default

– place for lots of bugs

● behaviour can be changes● it is preferred to properly handle config

changes– onSaveInstanceState(Bundle)

User Interface

● defined by hierarchy of views● layouts = containers

– LinearLayout

– RelativeLayout

– FrameLayout

– AdapterView – ListView, GridView, Spinner

● widgets = UI objects– Button, TextView, EditText

– WebView

List Widgets

● displays a list of items (some view)– ListView, Spinner, GridView, Gallery

● use adapter to bind list to data

Resources

● drawables – bitmaps, 9-patch png, state-list, layer list, shape drawable, ...

● layouts● strings● colors● menus● animations● arrays, ids, dimensions, raw, ...

Screen sizes and densities

● How to handle so many different devices?

Resource units

● dp/dip – density-independent pixel● sp – scale-independent pixel

Resources

● generated file R.java● resource ids● makes resources accessible in the code●

● resources can be created in several versions

– proper resource is selected according to current device configuration in runtime

Resource qualifiers

● screen density – ldpi, mdpi, hdpi, xhdpi

● screen size – small, normal, large, xlarge

● screen orientation – port, land

● language – en, cs, sk, ...

● version – v11, v14, ...

● since Android 3.2– w<N>dp – available screen width, w600dp

– h<N>dp – available screen height, h720dp

– sw<N>dp – smallest width (does not change with orientation change)

● combinations

Android version fragmentation

● How to handle different API levels avialable on devices?

● build target– project.properties

– target=android-16

● AndroidManifest.xml<uses-sdk

android:minSdkVersion="8"

android:targetSdkVersion="16" />

Android version fragmentation

if (Build.VERSION.SDK_INT <

Build.VERSION_CODES.GINGERBREAD) {

// only for android older than gingerbread

}

Android version fragmentationprivate boolean functionalitySupported = false;

static {

try {

checkFunctionalitySupported();

} catch (NoClassDefFoundError e) {

functionalitySupported = false;

}

}

private static void checkFunctionalitySupported() throws

NoClassDefFoundError {

functionalitySupported = android.app.Fragment.class != null;

}

Fragments

● a piece of application UI● fragment != activity● fragments used within activities● since Android 3.0● support library v4 backports it to Android 1.6+● introduced to support more flexible UI –

phones and tablets together in one app

Threads

● main thread = UI thread● do not block the UI thread● use worker threads for time consuming

operations ● UI toolkit not thread safe – never manipulate

UI from a worker thread

Menu

● Android pre 3.0 – menu hidden under menu button

● Android 3.0+ has ActionBar:– items can be displayed in the action bar

– if not enough space the bahaviour depends:● hidden under menu button, if the device has

menu button● otherwise an overflow icon created in the

action bar

● menu resource

Dialogs and Toasts

● Dialog – floating window screen– standard dialogs

– custom dialogs

– since fragments used via DialogFragment

● Toast – simple non-modal information displayed for a short period of time

– doesn't have user focus

Notifications

● a message that can be displayed to the user outside your normal UI

● displayed in notification area● user can open notification drawer to see the

details● app can define UI and click action on the

notification● NotificationCompat.Builder

THE END