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Java & Android
Java Fundamentals
Madis Pink
2016 Tartu
1
Agenda
» Brief background intro to Android
» Android app basics:
» Activities & Intents
» Resources
» GUI
» Tools
2
Android
» A Linux-based Operating System
» Announced by Google & the Open Handset
Alliance Nov 2007
» First device with Android 1.0 shipped in 2008
3
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
4
VMs on Android
» Dalvik - all Android versions up to 4.4, just-intime 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
5
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
6
Dex Toolchain(s)
» Dexer (dx) - transforms Java 7 bytecode
(.class) to dex
» Jack & Jill - Experimental direct Java
compilation to dex, supports Java 8
7
Dex & Dalvik Example
class Hello {
public static void main(String[] args) {
System.out.println("Hello world!");
}
}
8
Dex & Dalvik Example
$ javac Hello.java -target 1.7 -source 1.7
$ java Hello
Hello world!
9
Dex & Dalvik Example
$ javac Hello.java -target 1.7 -source 1.7
$ java Hello
Hello world!
$ dx --dex --output=out.dex Hello.class
10
Dex & Dalvik Example
$ javac Hello.java -target 1.7 -source 1.7
$ java Hello
Hello world!
$ dx --dex --output=out.dex Hello.class
$ adb push out.dex /data/local/tmp/out.dex
11
Dex & Dalvik Example
$ javac Hello.java -target 1.7 -source 1.7
$ java Hello
Hello 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 Hello
Hello world!
12
Anatomy of an App
Each 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
13
Anatomy of an App
» No main(String[])
» Components as entry points:
» Activities
» Services
» Broadcast receivers
» Content Providers
» These are defined in the AndroidManifest.xml
14
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
15
Intermission
all samples at
https://github.com/JavaFundamentalsZT/jf-android-samples
16
Activities
17
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
18
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
19
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!
20
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
21
Explicit Intents
public 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
22
Implicit Intents
public void sendFeedback() {
Uri uri = Uri.parse("mailto:[email protected]");
Intent i = new Intent(Intent.ACTION_SENDTO, uri);
startActivity(i);
}
» Used for general actions like Send email, Open a
webpage, Take a picture etc
23
Implicit Intents
24
Implicit Intents
public void openWebpage() {
Uri uri = Uri.parse("https://courses.cs.ut.ee/2016/javaFund/fall");
Intent i = new Intent(Intent.ACTION_VIEW, uri);
startActivity(i);
}
25
Implicit Intents
26
Defining an Activity
package org.zeroturnaround.jf.android;
import android.app.Activity;
public class HelloActivity extends Activity {
}
27
Defining an Activity
package 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();
}
}
28
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>
29
AndroidManifest.xml
The <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>
30
AndroidManifest.xml
The <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>
31
AndroidManifest.xml
The <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>
32
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>
33
34
More Information
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
35
Resources
36
37
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, ...
38
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
39
Drawables
» Placed in src/main/res/drawable
» Can be XML (describing shapes, colours,
gradients) or bitmaps
» Automatically scaled by the OS
40
Layouts
» Placed in src/main/res/layout
» XML files for describing UI
» More on these later :)
41
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
42
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)
43
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
44
Resource Qualifiers
Resource 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
45
Resources
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="org.zeroturnaround.jf.android" >
<application>
<!-- components go here -->
</application>
</manifest>
46
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>
47
Resources
<?xml version="1.0" encoding="utf-8"?>
<resources>
<string name="app_name">Hello</string>
<string name="hello_world">Hello World!</string>
</resources>
48
Resources
<application
android:label="Hello World">
49
Resources
<application
android:label="@string/app_name">
50
Resources
<application
android:label="@string/app_name"
android:icon="@drawable/ic_launcher">
51
Resources
// display our message
String msg = "Hello World!";
Toast.makeText(this, msg, Toast.LENGTH_SHORT).show();
52
Resources
// display our message
String msg = getResources().getString(R.string.hello_world);
Toast.makeText(this, msg, Toast.LENGTH_SHORT).show();
53
Resources
54
More Information
Resources overview - https://d.android.com/
guide/topics/resources/overview.html
55
GUI
56
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
57
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
58
Views
» TextView - displays text
» ImageView - displays images
» EditText - text input
» Button - clickable TextView with various states
59
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
60
Views
protected 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();
}
61
Views
Replace our toast with a TextView
// display our message
String msg = "Hello World!";
TextView root = new TextView(this);
root.setText(msg);
setContentView(root);
62
Views
src/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" />
63
Views
src/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);
64
Views
65
Views
Add 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" />
66
Views
Make 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" />
67
Views
68
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
69
Handling Events
Adding 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" />
70
Handling Events
Adding 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>
71
Handling Events
We 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();
}
});
72
Handling Events
73
More information
Layouts: https://d.android.com/guide/topics/ui/
declaring-layout.html
Handling events: https://d.android.com/guide/
topics/ui/ui-events.html
74
Tools
75
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
76
Android Studio Configuring SDK
Under 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
77
Android Studio Configuring SDK
Under 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)
78
Android Studio Configuring SDK
With that being done, press Apply, read through
and Accept both Android SDK license and Intel
licenses and press Next to install the components
79
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/
80
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
81
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
82
More Information
Android Studio - https://d.android.com/studio/
index.html
Android and Android Studio: Getting Started
(~10min video) - https://youtu.be/Z98hXV9GmzY
83
Homework 14
84
Homework 14
All the details are at:
https://github.com/javafundamentalszt/jf-hwandroid-calculator
Due 2016-12-05 23:59:59 Estonian time
Do not leave this for the last minute!
Help/questions: [email protected]
85
Links
Samples - 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
86
