Java & AndroidJava Fundamentals

Madis Pink2016 Tartu

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Agenda» Brief background intro to Android

» Android app basics:

» Activities & Intents

» Resources

» GUI

» Tools

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Android» A Linux-based Operating System

» Announced by Google & the Open Handset Alliance Nov 2007

» First device with Android 1.0 shipped in 2008

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Android» The primary language for writing apps is

actually Java

» The standard library is mainly Java 6 with a lot of Android-specific classes on top

» There are 25 API versions, most apps target Android 4.4 (API 19) or higher today

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VMs on Android» Dalvik - all Android versions up to 4.4, just-in-

time compilation added in Android version 2.2

» ART - New runtime with ahead-of-time compilation, shipped with Android 5.0 and later

» Both operate on DEX (Dalvik EXecutable) bytecode

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Dex Bytecode» Design goals

» Compilation target for .java sources

» Code size

» Interpreting performance

» Bytecode instructions operate on registers

» Many classes in a single .dex file

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Dex Toolchain(s)» Dexer (dx) - transforms Java 7 bytecode

(.class) to dex

» Jack & Jill - Experimental direct Java compilation to dex, supports Java 8

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Dex & Dalvik Exampleclass Hello { public static void main(String[] args) { System.out.println("Hello world!"); }}

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Dex & Dalvik Example$ javac Hello.java -target 1.7 -source 1.7$ java HelloHello world!

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Dex & Dalvik Example$ javac Hello.java -target 1.7 -source 1.7$ java HelloHello world!$ dx --dex --output=out.dex Hello.class

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Dex & Dalvik Example$ javac Hello.java -target 1.7 -source 1.7$ java HelloHello world!$ dx --dex --output=out.dex Hello.class$ adb push out.dex /data/local/tmp/out.dex

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Dex & Dalvik Example$ javac Hello.java -target 1.7 -source 1.7$ java HelloHello world!$ dx --dex --output=out.dex Hello.class$ adb push out.dex /data/local/tmp/out.dex$ adb shell dalvikvm -cp /data/local/tmp/out.dex HelloHello world!

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Anatomy of an AppEach app is an .apk file - a zip in disguise - with the following contents:

» AndroidManifest.xml - the manifest, describes the app

» classes.dex - the dex bytecode

» resources.arsc - compiled Android resources

» res/* - compiled layouts, PNG bitmaps, etc

» assets/* - blob assets: databases, audio files, etc

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Anatomy of an App» No main(String[])

» Components as entry points:

» Activities

» Services

» Broadcast receivers

» Content Providers

» These are defined in the AndroidManifest.xml

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Android Projects» Built with Gradle!

» src/main/java - Java sources

» src/main/res - Android resources

» src/main/AndroidManifest.xml - the manifest

» build.gradle - Gradle build file, describes how to build the app

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Intermissionall samples at

https://github.com/JavaFundamentalsZT/jf-android-samples

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Activities

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Activity» class * extends android.app.Activity

» Started with an Intent - a user action

» Represents a screen in an application

» Owns a View hierarchy (GUI objects)

» Handles user input events

» Instantiated by the framework

» Lifecycle controlled by the framework

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Activities Example - Email App» InboxActivity - lists all emails in Inbox

» ViewEmailActivity - view a single email

» ComposeActivity - compose/send a new email

» LoginActivity - log the user in

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Activity Lifecycle» Driven by the framework through calls to

specific Activity methods

» onCreate/onDestroy - activity created

» onStart/onStop - activity visible

» onResume/onPause - activity is "on top"

» When overriding any of these, make sure to call to super!

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Starting an Activity - Intents» All Activities are started by defining an Intent - an

object that represents user's intentions

» Sort of like a request that apps can respond to

» Requires a Context instance to send the Intent to the OS

» All components, including activities extend Context

» Two kinds of intents - explicit and implicit

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Explicit Intentspublic void clickHelp() { // launch HelpActivity of this app Intent i = new Intent(context, HelpActivity.class); context.startActivity(i);}

» Used to launch a specific activity on the device, usually within the same app

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Implicit Intentspublic void sendFeedback() { Uri uri = Uri.parse("mailto:jf@zeroturnaround.com"); Intent i = new Intent(Intent.ACTION_SENDTO, uri); startActivity(i);}

» Used for general actions like Send email, Open a webpage, Take a picture etc

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Implicit Intents

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Implicit Intentspublic void openWebpage() { Uri uri = Uri.parse("https://courses.cs.ut.ee/2016/javaFund/fall"); Intent i = new Intent(Intent.ACTION_VIEW, uri); startActivity(i);}

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Implicit Intents

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Defining an Activitypackage org.zeroturnaround.jf.android;

import android.app.Activity;

public class HelloActivity extends Activity {}

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Defining an Activitypackage org.zeroturnaround.jf.android;

import android.app.Activity;import android.os.Bundle;import android.widget.Toast;

public class HelloActivity extends Activity { protected void onCreate(Bundle savedInstanceState) { // always need to call super super.onCreate(savedInstanceState); // display our message String msg = "Hello World!"; Toast.makeText(this, msg, Toast.LENGTH_SHORT).show(); }}

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AndroidManifest.xml<?xml version="1.0" encoding="utf-8"?><manifest xmlns:android="http://schemas.android.com/apk/res/android" package="org.zeroturnaround.jf.android" > <application> <activity android:name="org.zeroturnaround.jf.android.HelloActivity"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application></manifest>

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AndroidManifest.xmlThe <manifest /> tag tells us that this is an app with the application ID org.zeroturnaround.jf.android

<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="org.zeroturnaround.jf.android" > <application> <!-- components go here --> </application></manifest>

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AndroidManifest.xmlThe <activity /> tag declares an Activity component with the classname org.zeroturnaround.jf.android.HelloActivity

<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="org.zeroturnaround.jf.android" > <application> <activity android:name="org.zeroturnaround.jf.android.HelloActivity"> <!-- optional intent filter goes here --> </activity> </application></manifest>

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AndroidManifest.xmlThe <intent-filter /> tag declares which implicit Intents our Activity handles, in this case it is the MAIN action under the LAUNCHER category

This makes our app visible in the Launcher app

<intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /></intent-filter>

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AndroidManifest.xml<?xml version="1.0" encoding="utf-8"?><manifest xmlns:android="http://schemas.android.com/apk/res/android" package="org.zeroturnaround.jf.android" > <application> <activity android:name="org.zeroturnaround.jf.android.HelloActivity"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application></manifest>

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More InformationActivities: https://d.android.com/guide/components/activities.html

Intents: https://d.android.com/guide/components/intents-filters.html

Manifest: https://d.android.com/guide/topics/manifest/manifest-intro.html

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Resources

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Resources» Placed in src/main/res folder

» Precompiled by aapt during the Gradle build

» Value resources - strings, floats, integers, booleans, ...

» Complex resources - arrays, plurals, ...

» File resources - bitmaps, XMLs, drawables, layouts, ...

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Value Resources<?xml version="1.0" encoding="utf-8"?><resources> <string name="app_name">Hello</string> <string name="hello_world">Hello World!</string></resources>

» Placed in src/main/res/values/<FILENAME>.xml, where <FILENAME> can be anything, like strings.xml

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Drawables» Placed in src/main/res/drawable

» Can be XML (describing shapes, colours, gradients) or bitmaps

» Automatically scaled by the OS

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Layouts» Placed in src/main/res/layout

» XML files for describing UI

» More on these later :)

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Accessing Resources from XML» Resources can be referenced in XML resources

(including the manifest) via @<type>/<identifier>

» A few examples:

» @string/app_name

» @drawable/ic_launcher

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Accessing Resources from Code» All resources get a runtime integer ID, placed in a class

called R

» Need to dereference through a Resources instance, obtained through a Context

» Example dereferences:

» getResources().getString(R.string.app_name)

» getResources().getDrawable(R.drawable.ic_launcher)

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Resource Qualifiers» Resource folders can have extra qualifiers with -suffixes

» values-et containing Estonian strings

» Framework decides at runtime which resource to use

» Also used to have custom layouts for tablets, different drawables for device densities, etc

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Resource QualifiersResource qualifier examples:

» res/layout-land for landscape layouts

» res/drawable-xhdpi, res/drawable-hdpi, res/drawable-mdpi for icons at various resolutions

» res/values-et, res/values-ru for localization

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Resources<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="org.zeroturnaround.jf.android" > <application> <!-- components go here --> </application></manifest>

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Resources<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="org.zeroturnaround.jf.android" > <application android:label="Hello World"> <!-- components go here --> </application></manifest>

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Resources<?xml version="1.0" encoding="utf-8"?><resources> <string name="app_name">Hello</string> <string name="hello_world">Hello World!</string></resources>

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Resources<application android:label="Hello World">

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Resources<application android:label="@string/app_name">

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Resources<application android:label="@string/app_name" android:icon="@drawable/ic_launcher">

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Resources// display our messageString msg = "Hello World!";Toast.makeText(this, msg, Toast.LENGTH_SHORT).show();

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Resources// display our messageString msg = getResources().getString(R.string.hello_world);Toast.makeText(this, msg, Toast.LENGTH_SHORT).show();

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Resources

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More InformationResources overview - https://d.android.com/guide/topics/resources/overview.html

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GUI

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GUI - Units» No absolute coordinates!

» Units:

» dip (dp) - density-independent pixels

» sp - scaled pixels, scale with the text size

» px - actual physical pixels

» Even with dp the sizes of screens vary wildly

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View Hierarchy» ViewGroup (container/node) and View (leaf node)

» View groups lay out their children, which could be nested groups

» Can be declared through code

» Can be inflated from XML layouts

» Use setContentView(View root) or setContentView(int layoutResId) to attach a hierarchy to an Activity

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Views» TextView - displays text

» ImageView - displays images

» EditText - text input

» Button - clickable TextView with various states

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ViewGroups» FrameLayout - simple layouts for framing

children

» LinearLayout - lays views out in a single row/column

» RelativeLayout - lays views out in relation to each other with rules

» ListView - scrolling a lot of similar views with caching

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Viewsprotected void onCreate(Bundle savedInstanceState) { // always need to call super super.onCreate(savedInstanceState); // display our message String msg = getResources().getString(R.string.hello_world); Toast.makeText(this, msg, Toast.LENGTH_SHORT).show();}

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ViewsReplace our toast with a TextView

// display our messageString msg = "Hello World!";TextView root = new TextView(this);root.setText(msg);setContentView(root);

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Viewssrc/main/res/layout/hello.xml:

<?xml version="1.0" encoding="utf-8"?><TextView xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:text="@string/hello_world" />

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Viewssrc/main/res/layout/hello.xml:

<?xml version="1.0" encoding="utf-8"?><TextView xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:text="@string/hello_world" />

... and in our HelloActivity.onCreate:

setContentView(R.layout.hello);

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Views

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ViewsAdd some padding with android:padding

<?xml version="1.0" encoding="utf-8"?><TextView xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:text="@string/hello_world" android:padding="16dp" />

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ViewsMake the font larger with android:textSize

<?xml version="1.0" encoding="utf-8"?><TextView xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:text="@string/hello_world" android:padding="16dp" android:textSize="32sp" />

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Views

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Handling Events» Views can be given generated IDs via

android:id="@+id/someIdentifier"

» This will generate a unique integer accessible via R.id.someIdentifier

» Use findViewById(int id) to find the view in code

» Note! Always returns View so might need to cast

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Handling EventsAdding a button to our view

<Button android:id="@+id/my_button" android:layout_width="match_parent" android:layout_height="match_parent" android:text="@string/click" />

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Handling EventsAdding a button to our view

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:padding="16dp" android:orientation="vertical">

<TextView android:layout_width="match_parent" android:layout_height="match_parent" android:text="@string/hello_world" android:textSize="32sp" />

<Button android:id="@+id/my_button" android:layout_width="match_parent" android:layout_height="match_parent" android:text="@string/click" />

</LinearLayout>

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Handling EventsWe can use setOnClickListener to attach a handler to the click event

setContentView(R.layout.hello);

// attach an OnClickListener to the view with id `my_button`Button myButton = (Button) findViewById(R.id.my_button);myButton.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Toast.makeText(v.getContext(), R.string.click, Toast.LENGTH_SHORT).show(); }});

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Handling Events

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More informationLayouts: https://d.android.com/guide/topics/ui/declaring-layout.html

Handling events: https://d.android.com/guide/topics/ui/ui-events.html

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Tools

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Android Studio in 5 minutes» The official IDE for Android development

» Based on IntelliJ IDEA Community Edition

» Download: https://d.android.com/studio/index.html

» Before opening any project, open Configure -> SDK Manager to download necessary SDK components for the homework

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Android Studio - Configuring SDKUnder the SDK Platforms tab, click Show Package Details and make sure the following items are checked in the Android 7.0 (Nougat) category:

» Android SDK Platform 24

» Sources for Android 24

» Google APIs Intel x86 Atom System Image

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Android Studio - Configuring SDKUnder the SDK Tools tab, click Show Package Details and make sure the following items are checked:

» 25.0.1 under Android SDK Build-Tools

» Android SDK Platform-Tools 25.0.1

» Android SDK Tools 25.2.3

» Intel x86 Emulator Accelerator (HAXM installer)

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Android Studio - Configuring SDKWith that being done, press Apply, read through and Accept both Android SDK license and Intel licenses and press Next to install the components

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Android Studio in 5 minutes» Import the homework/samples folder via Open an

existing Android Studio project

» Find the green '▶' next to a dropdown in the toolbar

» Studio will ask you to create an emulator, any emulator with the version later than 4.0.3 (API 15) will do

» Note: we've already downloaded the image for Nougat 7.0

» You should see the app on the emulator \o/

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Developing with a Device» Settings -> About phone

» Scroll down & tap Build number 7 times

» You are now a developer!

» Settings -> Developer options

» Make sure USB Debugging is enabled

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Gradle» Project layout similar to Maven

» Instead of XML the build is defined through a Groovy DSL

» No installation needed, gradlew will download Gradle for you

» gradlew build - builds the project

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More InformationAndroid Studio - https://d.android.com/studio/index.html

Android and Android Studio: Getting Started (~10min video) - https://youtu.be/Z98hXV9GmzY

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Homework 14

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Homework 14All the details are at:https://github.com/javafundamentalszt/jf-hw-android-calculator

Due 2016-12-05 23:59:59 Estonian time

Do not leave this for the last minute!

Help/questions: jf@zeroturnaround.com

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LinksSamples - https://github.com/JavaFundamentalsZT/jf-android-samples

Activities - https://d.android.com/guide/components/activities.html

Intents - https://d.android.com/guide/components/intents-filters.html

Manifest - https://d.android.com/guide/topics/manifest/manifest-intro.html

Resources overview - https://d.android.com/guide/topics/resources/overview.html

Layouts - https://d.android.com/guide/topics/ui/declaring-layout.html

Handling events - https://d.android.com/guide/topics/ui/ui-events.html

Android Studio - https://d.android.com/studio/index.html

Android and Android Studio: Getting Started (~10min video) - https://youtu.be/Z98hXV9GmzY

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