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From JavaEE to Android: Way in one click?

Sergii ZhukAndroid/Java Developer at DAXX BV

Kyiv, 2014-07-24

Android for beginners from the former JavaEE developer

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Agenda

• History and the market share• How to start• Application components• UI development• Working with a database• Build tools and continuous integration• Publishing

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Android: the history

• Founded in Palo Alto, CA in 2003• Acquired by Google in 2005 • First commercial smartphone: HTC Dream,

Oct 2008 • Driven by Linux Kernel • Open Source Project

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Android market share (2)

https://developer.android.com/about/dashboards/index.html

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How to start

• JDK• Android SDK• Java IDE + Android plugin• Gradle build system (optional)

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Typical project structure

src/ Source code files

res/ Application resources - drawable files, layout files, string values

bin/ Output directory of the build

gen/ Java files generated by Android Developer Tools like res codes

assets/ Raw asset files. You can navigate this directory in the same way as a typical file system, the original filename is preserved

libs/ Libraries

AndroidManifest.xml The control file that describes the nature of the application and each of its components

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The Manifest FileYour app must declare all its components in AndroidManifest.xml file. This file contains:

• user permissions the app requires (Internet access, local storage, …)

• the minimum API Level required by the app• hardware and software features used (camera,

bluetooth, …) • libraries the app needs to be linked (Google maps)• and more…

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Manifest file example<?xml version="1.0" encoding="utf-8"?><manifest xmlns:android="http://schemas.android.com/apk/res/android" package="org.sergez.splayer" android:versionCode="37" android:versionName="2.1"> <uses-sdk android:minSdkVersion="8" android:targetSdkVersion="19"/> <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/> <application android:icon="@drawable/ic_launcher" android:label="@string/app_name" android:debuggable="false" > <activity android:name=".activity.SimplePlayerActivity" android:label="@string/app_name“ android:theme="@style/Theme.Sherlock"> <intent-filter> <action android:name="android.intent.action.MAIN"/> <category android:name="android.intent.category.LAUNCHER"/> </intent-filter> </activity> <service android:name=".service.SimplePlayerService" android:enabled="true"/> </application></manifest>

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Application Resources

• Resources are separate from the source code

• For every resource a unique integer ID will be generated, which you can use as reference from code

• Ability to provide alternative resources for different device configurations

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Multiple screens support (1)

• Density-independent pixel (dp) - A virtual pixel unit to express layout dimensions or position in a density-independent way.

• px = dp * (dpi / 160) - for 160dpi screen

• “wrap_content” and “match_parent” flexible sizes

Multiple screens support (2)

• Alternative drawable resources for different screen densities

• Vector xml-defined graphics – put to default drawable folder

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Multiple screens support (3)Low density (120), ldpi

Medium density (160), mdpi

High density (240), hdpi

Extra high density (320), xhdpi

Small screen QVGA (240x320) 480x640

Normal screen WQVGA400 (240x400) WQVGA432 (240x432)

HVGA (320x480) WVGA800 (480x800) WVGA854 (480x854) 600x1024

640x960

Large screen WVGA800 (480x800) WVGA854(480x854)

WVGA800 (480x800) WVGA854 (480x854) 600x1024

Extra Large screen 1024x600 WXGA (1280x800)1024x7681280x768

1536x11521920x1152 1920x1200

2048x15362560x1536 2560x1600

http://developer.android.com/guide/practices/screens_support.html

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Application Resourcesexample

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Main UI components

Source: http://www.itcsolutions.eu/2011/08/27/android-tutorial-4-procedural-vs-declarative-design-of-user-interfaces/

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<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:padding="16dp"> <TextView android:text="@string/hello_world" android:layout_centerInParent="true" android:textSize="20sp" android:textColor="#FF444444" android:textStyle="bold|italic" android:layout_width="wrap_content" android:layout_height="wrap_content" /> </RelativeLayout>

Procedural vs. Declarative Design of UI (1)

/java/org/sergez/jugdemo1/MainActivity.java

/res/layout/activity_main.xml

@Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); }

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Procedural vs. Declarative Design of UI (2)/java/org/sergez/jugdemo1/MainActivity.java@Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); RelativeLayout mainLayout = new RelativeLayout(this); RelativeLayout.LayoutParams mainLayoutParams = new RelativeLayout.LayoutParams( ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT); mainLayout.setLayoutParams(mainLayoutParams); TextView textInfo = new TextView(this); textInfo.setText("Hello World!"); RelativeLayout.LayoutParams textLayoutParams = new RelativeLayout.LayoutParams( ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT); textLayoutParams.addRule(RelativeLayout.CENTER_IN_PARENT, RelativeLayout.TRUE); textInfo.setLayoutParams(textLayoutParams); textInfo.setTextSize(20); textInfo.setTypeface(Typeface.SANS_SERIF, Typeface.BOLD_ITALIC); textInfo.setTextColor(Color.DKGRAY); mainLayout.addView(textInfo); setContentView(mainLayout); }

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Common layouts

Organizes its children into a single horizontal or vertical row. It creates a scrollbar if the length of the window exceeds the length of the screen.

Enables you to specify the location of child objects relative to each other (child A to the left of child B) or to the parent (aligned to the top of the parent).

Linear Layout Relative Layout

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Common layouts – adapter-based

List View Grid View

Displays a scrolling single column list

Displays a scrolling grid of columns and rows

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App Components

Each component is a different point through which the system can enter your app:• Activities• Services• Content providers• Broadcast receivers

http://developer.android.com/guide/components/fundamentals.html

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Activity

• Provides a screen with which users can interact in order to do something

• One activity in an application is specified as the "main" activity - launching the application

• When an activity is stopped because a new activity starts, it is notified of this change in state through lifecycle callback methods

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Activity lifecycle

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Service

• Perform long-running operations in the background and does not provide a user interface

• Runs in the main thread of its hosting process—the service does not create its own thread and does not run in a separate process (unless you specify otherwise).

• Should be defined in AndroidManifest.xml

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Service workflow

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Save application data

• SharedPreferences (key/value pairs)

• Files (internal/external storage)

• SQLite database

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SQLite database• Serverless• Stores data in one database file• Has no fixed column length• Uses cross-platform database files• Is used not only by Android but also by Apple’s

iOS and Blackberry’s system

http://www.grokkingandroid.com/sqlite-in-android/

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SQLite database

• Every app developer can rely on SQLite being present on an Android system

• Android doesn’t use JDBC

• You can’t use another database in Android

• Not encrypted by default, can be accessed on rooted devices:

/data/data/<package-name>/databases

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SQLite for Android: data types

Type Meaning

INTEGERAny number which is not a floating point number

REALFloating-point numbers (8-Byte IEEE 754 – i.e. double precision)

TEXTAny String and also single characters (UTF-8, UTF-16BE or UTF-16LE)

BLOBA binary blob of data

http://www.grokkingandroid.com/sqlite-in-android/

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Content provider (1)

• Presents data to external applications as one or more tables that are similar to the tables found in a relational database

• Android itself includes content providers for data such as audio, video, images, and Contacts

• Thread safe, asynchronous

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Content provider (2)

• An application accesses the data from a content provider with a ContentResolver client object which provides the basic CRUD

• Should be declared in AndroidManifest.xml

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Content provider (3)public static int markStatus(Context context,

String localId, Status status) {ContentValues values = new ContentValues();String where = DBHelper.COL_UUID + " = ?";String[] selectionArgs = new String[]{

String.valueOf(localId)};values.put(DBHelper.COL_STATUS, status.ordinal());return context.getContentResolver().update(

MyContentProvider.CONTENT_URI_MYRESOURCE, values, where, selectionArgs

);}

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Broadcast receiver

• Allows to register for system or application events

• Operates with Intent which is a lightweight messaging object

• Normal broadcast: asynchronous - all receivers of the broadcast are run in an undefined order, often at the same time

• Ordered broadcast: delivered to one receiver at a time, order can be controlled

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System broadcasts example

Event Description

Intent.ACTION_BOOT_COMPLETED Boot completed.

Intent.ACTION_POWER_CONNECTED Power got connected to the device.

Intent.ACTION_POWER_DISCONNECTED Power got disconnected from the device.

Intent.ACTION_BATTERY_LOW Triggered on low battery. Typically used to reduce activities in your app which consume power.

Intent.ACTION_PHONE_STATE_CHANGED The call state (cellular) on the device has changed

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Use Case: Interaction with backend

• Synchronous HTTP request in the separate thread- OR use external library (Retrofit, Volley, Enroscar)

• Parse result (for json - GSON is de-facto standard)

• Post result to the UI

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Use Case: integration with social networks

• REST API with OAuth authorization

• Vendor-provided libraries

• Third-party libraries

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Use Case: integration with social networks - library

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Run your app

• Android SDK Emulator

• VirtualBox ones like Genymotion

• Real device – must have!

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How to build your app

• In IDE

• Old-fashioned build tools: Ant, Maven

• Gradle

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Gradle

• Good IDE integration and single build system

• Built-in dependency management through Maven and/or Ivy.

• Built-in signing for applications

• Backward compatibility may not work properly sometimes

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Gradle build script examplebuildscript { repositories { mavenCentral() } dependencies { classpath 'com.android.tools.build:gradle:0.9.+' } } apply plugin: 'android' repositories { mavenCentral() } dependencies { compile 'com.actionbarsherlock:actionbarsherlock:4.4.0@aar' compile 'com.android.support:support-v4:18.0.+' } android { compileSdkVersion 19 buildToolsVersion "19.1.0" lintOptions { abortOnError false } }

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Demo project

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Testing• Manual

• Unit testing – JUnit 3 out of the box

• Robotium: blackbox UI testing in emulator

• Robolectric: tests are to be run outside the emulator – in a JVM, not in the Dalvik VM

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Continuous integration in general

• Maintain a code repository• Automate the build• Make the build self-testing• Make it easy to get the latest deliverables• Everyone can see the results of the latest build• And more

http://martinfowler.com/articles/continuousIntegration.html

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Continuous integration: mainstream for Android

• Jenkins CI

• Travis CI

• CIsimple

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Where to publish your app

• Google Play Store

• Samsung Apps

• Amazon Appstore for Android

• Smaller distribution networks

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Publish on Google Play Store

• Live demo

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What to read & try

• https://developer.android.com• http://android-developers.blogspot.com/• Dig in sources• CommonsGuy blog & book• Coursera courses: Programming Cloud Services for Android Handheld Systems and others

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Thanks!

Contact me:sergey.public@gmail.comhttp://ua.linkedin.com/in/sergiizhukhttp://fb.com/sergii.zhuk