•  IntroducBon to the Android PlaDorm

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SERIOUS ABOUT SOFTWARE

Android App Development

Juha-‐Ma5 Liukkonen

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IntroducBon to Android

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Android Basics

•  Android is a Linux based plaDorm

•  PlaDorm = kernel, libraries, system services, user interface framework

•  Linux kernel provides hardware abstracBon and core services

•  Standard libraries: WebKit, SQLite, OpenSSL, …

•  The C library is BSD based – Linux “standard” is GNU glibc

•  Primary applicaBon environment: Java VM

•  NaBve components for performance

•  Can use all system resources

•  Must be compiled for each hardware target separately

•  Java applicaBons for easy portability

•  Google’s Dalvik VM performs run-‐Bme translaBon to machine code

•  Limited memory footprint, limited access to hardware resources

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Android Architecture

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Android APIs and compaBbility

•  API = ApplicaBon Programming Interface

•  Sets of library rouBnes you can call from your applicaBon

•  Provide access to system services and applicaBon framework uBliBes

•  Android has 7 API levels in acBve use

•  API 4 = Android 1.6, …, API 11 = Android 3.0

•  API levels are forwards compa,ble, i.e. an app wriNen for API level 4 will work on Android 1.6+

•  Varying device features

•  CPU speed, screen sizes, touchscreen/keypad, microphone, …

•  Your app must declare what features it requires, so that it can only be installed on devices with the required features present

This is what is meant by

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Android Next GeneraBon

•  Android <3.0 is intended for touch-‐screen mobile phones

•  Screen sizes up to 4”, resoluBon up to 800x480

•  Somewhat clunky support for keypad-‐only soluBons

•  Usually 3 hardware keys – back, home, menu

•  Physical keyboard supported as an addiBonal input method

•  Android 3.0 is intended for touch-‐screen tablets

•  Screen sizes from 7” up, resoluBon from 800x480 up

•  Quite diﬀerent UI paradigm from <3.0

•  Hardware keys implemented as touch keys

•  Merge of the two lines ~ 3.1 (“Ice-‐cream Sandwich”)

This does not exactly help with the fragmentation part.

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Android UI basics

Home screen contains widgets and shortcuts. Top of screen

Application menu contains launcher icons for all apps installed into the device.

Long press usually opens a pop-up context menu.

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Apps versus widgets

•  ApplicaBons in Android are full-‐screen

•  In Android 3.0, they may be shown in “thumbnail” size in the task switcher

•  No concept of overlapping windows

•  Widgets are parBal-‐screen mini-‐applicaBons

•  Limited layout opBons, limited UI elements

•  Usually show a minimal view to some app’s status or data, e.g. currently playing music, weather, or news headlines

•  An applicaBon may include also a widget

•  Basically, a mini-‐view to the app content, or a controller interface to a background service

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Android Concepts

for SW Designers

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App model for mobile world

•  Android apps are not regular Java SE/ME/EE apps

•  Language used is Java

•  System libraries are Android speciﬁc

•  There is no public sta,c void main()

•  ApplicaBon components derived from 1 of 4 Android base classes

•  AcBvity: represents an UI view

•  Service: a background component doing e.g. network acBvity

•  Content provider: manages shared app data, e.g. an SQLite database

•  Broadcast receiver: reacts to system state changes

•  An app may have 1 or more of each kind of components

•  The system may suspend or kill components based on system resource state (~component-‐level garbage collecBon)

Google is using some Java sources in conflict with the original license. Lawsuit with Oracle is in progress.

Key for mobile app: save power.

Do work only when you have to.

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SDK and NDK

•  SDK = Sorware Development Kit

•  Consists of Java compiler, libraries, ant, packaging tools

•  Used to build installable applicaBon packages (.apk) from Java source ﬁles

•  NDK = NaBve Development Kit, add-‐on to the SDK

•  Consists of C/C++ compiler, libraries, headers, make, packaging tools

•  Used to build installable applicaBon packages (.apk) from C/C++ source ﬁles

•  Both available to mulBple plaDorms

•  Linux, Mac OS X, Windows

NDK until Android 2.3 was rather limited.

Now can build shared libraries etc.

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Eclipse

•  IDE = Integrated Development Environment

•  Android SDK integrates with and is managed from Eclipse

•  Eclipse is a Java-‐based IDE available for all common plaDorms

•  Code compleBon, online help, debugger, deployment to target device, …

They used to say Emacs comes with the kitchen sink…

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Ge5ng ready to develop

•  Follow instrucBons in hNp://developer.android.com/sdk/index.html

•  Install Eclipse (from hNp://www.eclipse.org/downloads/ )

•  Install the SDK starter package (from the developer.android.com URL)

•  Install the ADT (Android Developer Tools) plugin from Eclipse

•  Conﬁgure the Eclipse ADT plugin to ﬁnd your SDK installaBon

•  Use the ADT to install SDK components, e.g. support for diﬀerent API levels

•  OpBonal: download and install NDK

•  There is a lot to download and install

•  Reserve an hour or so to get everything set up Step 1: Get started Step 2: …

Step 3: Victory!

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App Elements

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The Manifest

•  AndroidManifest.xml deﬁnes your applicaBon

•  Java package name of your applicaBon

•  AcBviBes and other components your applicaBon may contain

•  Device features that your applicaBon may require

•  Intent ﬁlters – will your app appear in the app menu, which acBons to associate to, et cetera

•  Permissions your app needs in order to work

•  Permissions your app requires from others to serve their intent requests

•  Minimum API level required

•  List of libraries your app needs to be linked against

•  Crucial to understand for all but the most trivial apps

•  Eclipse creates a skeleton for you, enough for Hello World

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Resources

•  Stored in subdirectory res in your applicaBon source tree

•  Drawables: icons, bitmaps, animaBons, colors

•  Layout: XML view deﬁniBons

•  Menu: XML menu deﬁniBons

•  Strings: text strings that appear in your user interface

•  LocalizaBon

•  Provide localized resources in a subdirectory res/resourcetype-‐localename, e.g.

res/values-‐ﬁ

•  Hardware variance adaptaBon

•  Provide variant resources in a subdirectory res/resourcetype-‐variant, e.g. res/

drawables-‐xlarge

•  Variants recognized for API levels, DPI, primary input method, …

<?xml version="1.0" encoding="utf-8"?>

<string name="hello">Hello!</string>

</resources>

res/values/strings.xml

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Manifest example

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

package="com.example.android.home">

<uses-permission android:name="android.permission.GET_TASKS"/>

<uses-permission android:name="android.permission.READ_CONTACTS"/>

<uses-permission android:name="android.permission.SET_WALLPAPER" />

<uses-permission android:name="android.permission.INTERNET" />

<application android:persistent="true"

android:label="@string/home_title"

android:icon="@drawable/ic_launcher_home">

<activity android:name="Home"

android:theme="@style/Theme"

android:launchMode="singleInstance"

android:stateNotNeeded="true">

<intent-filter>

</intent-filter>

</activity>

<activity android:name="Wallpaper"

android:label="Wallpaper"

android:icon="@drawable/bg_android_icon">

<intent-filter>

</intent-filter>

</activity>

Refers to the home_title string in localized res/values

Refers to the ic_launcher_home drawable in res/drawables variant

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View DeﬁniBon XML

•  Deﬁnes your AcBvity view layout

•  WYSIWYG editor in Eclipse to make life easier

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

android:layout_width="fill_parent"

android:layout_height="fill_parent"

android:orientation="vertical" >

<TextView android:id="@+id/text"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="Hello, I am a TextView" />

<Button android:id="@+id/button"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="Hello, I am a Button" />

</LinearLayout>

public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);

setContentView(R.layout.main_layout);

}

“R” is the class for accessing resources from Java code.

res/layout/main_layout.xml

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Java Code

•  Deﬁnes your component behavior

•  Classes derived from AcBvity, or other Android base classes

•  “TradiBonal” Java programming to put the resources into use

package com.example.android.miniapp;

import android.app.Activity;

…

public class MiniApp extends Activity { @Override

protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);

setContentView(R.layout.main_layout);

} }

com/example/android/miniapp/MiniApp.java

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CreaBng and Deploying an App

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Basic steps

•  In Eclipse, File -‐> Create New Project, Android ApplicaBon

•  At this point you ﬁll in a lot of the manifest content, e.g. API level

•  Eclipse generates the directory structure and skeleton ﬁles for you

•  Add resources

•  For example, a picture (right-‐click on project, choose Import)

•  Open the layout/main.xml and add some user interface elements

•  E.g. a buNon; take note which resource idenBﬁers the elements get

•  Add funcBonality to your Java code

•  For example, a buNon click handler

•  Run your app!

•  Either in emulator, or over USB on your Android device

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Eclipse: create Android project

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IniBal Manifest content

Several example apps that can be used as templates – utilize them!

Android API level. “Google APIs” = APIs to access Google cloud services such as Maps.

App name, Java package name.

The wizard can create an Activity skeleton for you.

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ResulBng manifest

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Eclipse: visual UI builder

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UI elements available

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Add UI elements

Simply drag-and-drop an element from the palette to your layout.

This is the identifier you use in Java code to refer to the element (R.id.button1).

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Add resources

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And voilá!

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LocalizaBon

When the UI is complete, copy-paste the values directory to values-locale and localize the string values.

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Eclipse: create Java code

Skeleton Activity created by the Wizard. Note how UI elements are referenced using their id.

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Eclipse: run on Target!

Click the “Run” button in the Eclipse toolbar.

Be patient, the emulator takes a while to start.

If you have an Android device connected using USB, your app will run directly in your device.

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Advanced programming topics

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State saving

•  Android will kill your components if resources are scarce

•  Your app should implement the onSaveInstanceState() and

onRestoreInstanceState() methods to save e.g. currently entered data

•  You can be proacBve and handle content in onPause() and onResume() (app going to background / resuming to foreground)

•  State is saved into a Bundle

•  As name-‐value pairs

•  Using the putString() APIs (putArray, putInt, putBoolean, …)

•  The Bundle is provided to your onCreate() method as parameter

•  Is null if there is no saved state

•  Otherwise can be accessed using the getString() APIs

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Game programming

•  Simple games can be wriNen using Java

•  Limited amount of memory available

•  Limited support for hardware acceleraBon

•  Possibly accessing naBve components using JNI

•  Graphics or memory intensive apps require naBve code

•  Can uBlize all memory

•  Can access GL/ES directly

•  Can uBlize hardware features such as NEON (ARM vector instrucBons)

•  Diﬀerences in Android 3.0

•  UI acceleraBon with a boolean ﬂag in manifest, no naBve code required

•  Full OpenGL based games sBll need to go naBve

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DistribuBng your App

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The Android Market

•  An on-‐line app store

•  Accessible to most Android devices out there, via the Market app

•  Hosts around 200.000 Btles

•  Most Btles are ringtones, wallpapers, assorted uselessness – but some real gems are included

•  Has exceeded iPhone app store revenues for some developers in 2011

•  Ge5ng your app to Market is easy

•  Test your app thoroughly ﬁrst!

•  Export your app from Eclipse, your .apk gets digitally signed and opBmized for distribuBon

•  Go to hNp://market.android.com/publish

•  You can also use other means to deliver .apk ﬁles to customers

•  InstallaBon not limited to Market

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In Conclusion

•  Android is a funcBonal mobile device plaDorm

•  Many aspects perpetually in classic Google “beta” state

•  But it’s out there, in rapidly increasing numbers

•  The fragmentaBon causes some headaches to app developers

•  Developer tools are funcBonal

•  If you are familiar with Eclipse, developing for Android should be a breeze

•  Android online documentaBon is comprehensive and clear

•  Lots of examples provided with the SDK

•  Android oﬀers rich APIs

•  MulBmedia, VoIP, Google services, …

•  Easy to create reasonably complex apps, possible to create even very demanding ones

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• IntroducBon to the Android PlaDorm

SERIOUS ABOUT SOFTWARE

Android App Development

Juha-­‐Ma5 Liukkonen

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