Android development - the basics, MFF UK, 2012

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 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" />

if (Build.VERSION.SDK_INT <
Build.VERSION_CODES.GINGERBREAD) {
// only for android older than gingerbread
}

private 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

Android development - the basics, MFF UK, 2012

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