Groovy on Android -- DroidCon Paris 2014

Groovy
on Android
Guillaume Laforge
Groovy project lead (at Pivotal)
@glaforge

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Groovy
on Android
Guillaume Laforge
Groovy project lead (at Pivotal)
@glaforge
I’ll put the slides online on
speakerdeck.com/glaforge

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Total
Android
Newbie!

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Android is in the
Java stone age
state

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Is there
something we
can do about it?

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Yes, Groovy!

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New York Times — Getting Groovy with Android
4

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4
http://bit.ly/nyt-groovy

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5

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5
New York Times recruits a
Groovy / Android expert
http://bit.ly/nyt-job

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What does NYT likes about Groovy on Android?
• No Java 8, no lambda on Android…
6
Func0 func = new Func0() {
@Override
public String call() {
return "my content";
}
};
Async.start(func);

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7
!
!
!
!
!
!
Async.start { "my content" }

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7
!
!
!
!
!
!
Async.start { "my content" }
Good bye annonymous
inner classes!

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!
• Groovy code more concise and more readable

!
• but just as type-safe as needed! 
(with @TypeChecked)

!
• but just as fast as needed! 
(with @CompileStatic)
8

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@glaforge — Groovy on Android
Brief overview of Groovy

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Brief overview of Groovy
You probably know it
through Gradle already!

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Groovy — a multi-faceted language
Open-source project
(Apache 2 licensed)
!
• http://groovy.codehaus.org/

• http://beta.groovy-lang.org/
10

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Open-source project
(Apache 2 licensed)
!
• http://groovy.codehaus.org/

• http://beta.groovy-lang.org/
10
New « shiny » website
coming soon!

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Alternative language  
for the JVM
11

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for the JVM
11
An alternative
language for the
JVM

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for the JVM
11
With 3 million
downloads a year

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Closely  
resembles  
Java
12

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Closely  
resembles  
Java
12
Java code is also
valid Groovy code!

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Closely  
resembles  
Java
12
But Groovy
goes beyond!

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Multiple  
programming  
flavors
13

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Multiple  
programming  
flavors
13
Object-oriented

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Multiple  
programming  
flavors
13
Dynamic

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Multiple  
programming  
flavors
13
Functional

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Multiple  
programming  
flavors
13
Statically type checked
and / or compiled

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Seamless Java integration 
& interoperability
14

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Seamless Java integration 
& interoperability
14
No bridge to cross
between languages

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Let’s get started?

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With a Hello World?
16

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Android Studio
17

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Android Studio
17
Click on « New Project »

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Android Studio
18

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Android Studio
18
Fill in the project details

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Android Studio
19

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Android Studio
19
Choose your target
platform

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Android Studio
20

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Android Studio
20
Create a  
blank activity

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Android Studio
21

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Android Studio
21
Details for your
new activity

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Android Studio
22

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Android Studio
22
Now let’s
have fun!

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Modify your app’s Gradle build
23
apply plugin: 'com.android.application'
!
android {
compileSdkVersion 20
buildToolsVersion "20.0.0"
!
defaultConfig {
applicationId "com.appspot.glaforge.hellogroovyworld"
minSdkVersion 15
targetSdkVersion 20
versionCode 1
versionName "1.0"
}
buildTypes {
release {
runProguard false
proguardFiles getDefaultProguardFile('proguard-android.txt'),  
'proguard-rules.pro'
}
}
}
!
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
}

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23
!
android {
!
defaultConfig {
minSdkVersion 15
targetSdkVersion 20
versionCode 1
versionName "1.0"
}
buildTypes {
release {
runProguard false
}
}
}
!
dependencies {
}
buildscript {
repositories {
jcenter()
}
dependencies {
classpath 'com.android.tools.build:gradle:0.12.2'
classpath 'me.champeau.gradle:gradle-groovy-android-plugin:0.3.0'
}
}

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23
!
android {
!
defaultConfig {
minSdkVersion 15
targetSdkVersion 20
versionCode 1
versionName "1.0"
}
buildTypes {
release {
runProguard false
}
}
}
!
dependencies {
}
apply plugin: 'me.champeau.gradle.groovy-android'
buildscript {
repositories {
jcenter()
}
dependencies {
}
}

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23
!
android {
!
defaultConfig {
minSdkVersion 15
targetSdkVersion 20
versionCode 1
versionName "1.0"
}
buildTypes {
release {
runProguard false
}
}
}
!
dependencies {
}
compile 'org.codehaus.groovy:groovy:2.4.0-beta-3:grooid'
apply plugin: 'me.champeau.gradle.groovy-android'
buildscript {
repositories {
jcenter()
}
dependencies {
}
}

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Java to Groovy…
• Rename your activity from .java to .groovy

!
• Remove…

• public and return keywords

• some parentheses

• use the property notation

• getMenuInflater() becomes menuInflater

• use interpolated strings

• and more.
24

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Java to Groovy…
25
import android.app.Activity
import android.os.Bundle
import android.view.*
!
class HelloGroovyWorld extends Activity {
protected void onCreate(Bundle savedInstanceState) {
super.onCreate savedInstanceState
setContentView R.layout.activity_hello_groovy_world
}
!
boolean onCreateOptionsMenu(Menu menu) {
menuInflater.inflate R.menu.hello_groovy_world, menu
true
}
!
boolean onOptionsItemSelected(MenuItem item) {
int id = item.itemId
if (id == R.id.action_settings) {
return true
}
super.onOptionsItemSelected item
}

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Run your Groovy-powered app in the emulator
26

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What about weight?
On a demo application (conference agenda)
27
Artifact Size
Groovy JAR 4.5 MB
Generated APK 2 MB
After ProGuard
1 MB
(8K methods)

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ProGuard rules
28
-dontobfuscate
-keep class org.codehaus.groovy.vmplugin.**
-keep class org.codehaus.groovy.runtime.dgm*
-keepclassmembers class org.codehaus.groovy.runtime.dgm* {
*;
}
-keepclassmembers class ** implements
org.codehaus.groovy.runtime.GeneratedClosure {
*;
}
-dontwarn org.codehaus.groovy.**
-dontwarn groovy**

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How does the Groovy support work?

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Standard process
30
Compile-time
Runtime

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Standard process
30
Compile-time
Runtime
.class

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Standard process
30
Compile-time
Runtime
.class .dex

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Standard process
30
Compile-time
Runtime
.class .dex .apk

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First attempt — DiscoBot
31
Compile-time
Runtime

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31
Compile-time
Runtime
.apk

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31
Compile-time
Runtime
.class
.apk

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31
Compile-time
Runtime
.class .jar
.apk

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31
Compile-time
Runtime
.class .jar .dex
.apk

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31
Compile-time
Runtime
.class .jar .dex
.apk
« Ruboto » approach,
slow & inneficient

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New process — just like Java!
32
Compile-time
Runtime

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32
Compile-time
Runtime
.class

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32
Compile-time
Runtime
.class .dex

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32
Compile-time
Runtime
.class .dex .apk

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Evaluating Groovy code at runtime
33
Compile-time
Runtime
.class .dex .apk

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33
Compile-time
Runtime
.class .dex .apk
.class

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33
Compile-time
Runtime
.class .dex .apk
.class .jar

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33
Compile-time
Runtime
.class .dex .apk
.class .jar .dex

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What does Groovy bring?

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35
Optional

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35
Optional
Semi-colons

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35
Optional
Parentheses

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35
Optional
Typing

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35
Optional
return keyworkd

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35
Optional
public keyworkd

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From Java to Groovy…
36
public class Greeter {
private String owner;
!
public String getOwner() {
return owner;
}
!
public void setOwner(String owner) {
this.owner = owner;
}
!
public String greet(String name) {
return "Hello " + name + ", I am " + owner;
}
}
!
Greeter greeter = new Greeter();
greeter.setOwner("Guillaume");
!
System.out.println(greeter.greet("Marion"));

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From Java to Groovy…
36
public class Greeter {
private String owner;
!
public String getOwner() {
return owner;
}
!
public void setOwner(String owner) {
this.owner = owner;
}
!
public String greet(String name) {
return "Hello " + name + ", I am " + owner;
}
}
!
Greeter greeter = new Greeter();
greeter.setOwner("Guillaume");
!
System.out.println(greeter.greet("Marion"));
class Greeter {
String owner
!
String greet(String name) {
"Hello ${name}, I am ${owner}"
}
}
!
def greeter = new Greeter(owner: "Guillaume")
!
println greeter.greet("Marion")

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Special Groovy syntax sugar — special operators
37

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37
// Groovy truth
// if (s != null && s.length() > 0) {...}
if (s) { ... }
!
// Elvis
def name = person.name ?: "unknown"
!
// save navigation
order?.lineItem?.item?.name

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// Groovy truth
// if (s != null && s.length() > 0) {...}
if (s) { ... }
!
// Elvis
!
// save navigation
if (person.name != null &&
person.name.length() > 0)

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37
// Groovy truth
// if (s != null && s.length() > 0) {...}
if (s) { ... }
!
// Elvis
!
// save navigation
Copied by Swift, C#  
and CoffeeScript!

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37
// Groovy truth
// if (s != null && s.length() > 0) {...}
if (s) { ... }
!
// Elvis
!
// save navigation
order?.lineItem?.item?.name Anything null in the
chain? Null

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37
// Groovy truth
// if (s != null && s.length() > 0) {...}
if (s) { ... }
!
// Elvis
!
// save navigation
Better NPEs: Cannot get
property name on null object

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Special Groovy syntax sugar — collections, regex, closures
38
// lists
def list = [1, 2, 3, 4, 5]
!
// maps
def map = [a: 1, b: 2, c: 3]
!
// regular expressions
def regex = ~/.*foo.*/
!
// ranges
def range 128..255
!
// closures
def adder = { a, b -> a + b }

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Builders

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Builders With closures come
Groovy « builders »!

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Groovy builders — XML, JSON… Android views & layouts!
40
import groovy.json.*
!
def json = new JsonBuilder()
json.person {
name 'Guillaume'
age 37
daughters 'Marion', 'Erine'
address {
street '1 Main St'
zip 75001
city 'Paris'
}
}

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Groovy builders — XML, JSON… Android views & layouts!
40
!
def json = new JsonBuilder()
json.person {
name 'Guillaume'
age 37
daughters 'Marion', 'Erine'
address {
street '1 Main St'
zip 75001
city 'Paris'
}
}
{
"person": {
"name": "Guillaume",
"age": 37,
"daughters": [
"Marion",
"Erine"
],
"address": {
"street": "1 Main St",
"zip": 75001,
"city": "Paris"
}
}
}

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HTTP GET and JSON parsing in 4 lines
41
!
def url = "https://api.github.com/repos" + 
"groovy/groovy-core/commits"
!
def commits = new JsonSlurper().parseText(url.toURL().text)
!
assert commits[0].commit.author.name == 'Cedric Champeau'

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41
!
!
!
An HTTP GET
in a one-liner!

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41
!
!
!
No complex object graph marshalling!

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Annotations

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Annotations
Actually, code transformations
triggered by annotations

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Annotations
Actually, code transformations
triggered by annotations
No APT, sorry!

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AST transformations — only a short list!
Code generation
• @ToString

• @EqualsAndHashCode

• @Canonical

• @TupleConstructor

• @InheritConstructors

• @Category

• @Lazy

• @Sortable

• @Builder

!
!
Class design
• @Delegate

• @Immutable

• @Memoized

• @Singleton

!
Compiler directives
• @AnnotationCollector

• @DelegatesTo

• @TypeChecked

• @CompileStatic

• @TailRecursive
43

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AST transformations — @Immutable
Implement immutability by the book

!
• final class

• tuple-style constructor

• private final backing fields

• defensive copying of collections

• equals() and hashCode() methods

• toString() method

• ...
44

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• A person class

• a String name

• an int age
45
public final class Person {
private final String name;
private final int age;
!
public Person(String name, int age) {
this.name = name;
this.age = age;
}
!
public String getName() {
return name;
}
!
public int getAge() {
return age;
}
!
public int hashCode() {
return age + 31 * name.hashCode();
}
!
public boolean equals(Object other) {
if (other == null) {
return false;
}
if (this == other) {
return true;
}
if (Person.class != other.getClass()) {
return false;
}
Person otherPerson = (Person)other;
if (!name.equals(otherPerson.getName()) {
return false;
}
if (age != otherPerson.getAge()) {
return false;
}
return true;
}
!
public String toString() {
return "Person(" + name + ", " + age + ")";
}
}

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• A person class

• a String name

• an int age
46
import groovy.transform.*
!
@Immutable
class Person {
String name
int age
}

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AST transformations
47

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AST transformations
47
Groovy allows
you to be lazy

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AST transformations
47
The compiler will do
the job for you

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AST transformations
47
More concise, more
readable code

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AST transformations
47
Less stuff to maintain
and worry about

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Traits
• Like interfaces, but with method bodies
– similar to Java 8 interface default methods

• Elegant way to compose behavior

– multiple inheritance without the « diamond » problem

• Traits can also be stateful

– traits can have properties like normal classes

• Compatible with static typing and static compilation
– class methods from traits also visible from Java classes

• Also possible to implement traits at runtime 48

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Traits — example: melix / speakertime
49
@CompileStatic
class PresentationActivity extends Activity
implements GoogleApiProvider {
// ...
protected void onCreate(Bundle savedState) {
super.onCreate(savedState)
// ...
createGoogleApi()
}
!
protected void onStart() {
super.onStart()
connectGoogleApi()
}
!
protected void onStop() {
super.onStop()
disconnectGoogleApi()
}
// ...
@CompileStatic
trait GoogleApiProvider {
GoogleApiClient googleApiClient
!
void createGoogleApi() { /* ... */ }
!
void connectGoogleApi() { /* ... */ }
!
void disconnectGoogleApi() { /* ... */ }
}

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Compare Java and Groovy
50

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Event listeners
51
button.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View view) {
Log.i(tag, "clicked!")
}
})

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Event listeners
51
button.onClickListener = {
}
button.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View view) {
}
})

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Properties and equality
52
if (intent.getAction().equals(Intent.ACTION_VIEW)) {
Log.i(tag, "view");
}

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Properties and equality
52
if (intent.getAction().equals(Intent.ACTION_VIEW)) {
Log.i(tag, "view");
}
if (intent.action == Intent.ACTION_VIEW) {
Log.i(tag, "view")
}

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Groovy Development Kit methods
53
new Thread() {
public void run() {
// …
}
}.start();

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Groovy Development Kit methods
53
new Thread() {
public void run() {
// …
}
}.start();
Thread.start {
// …
}

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Groovy’s with {} method
54
view = new TextView(context);
view.setText(name);
view.setTextSize(16f);
view.setTextColor(Color.WHITE);

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Groovy’s with {} method
54
view = new TextView(context);
view.setText(name);
view.setTextSize(16f);
view.setTextColor(Color.WHITE);
view = new TextView(context)
view.with {
text = name
textSize = 16f
textColor = Color.WHITE
}

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Groovy Truth and GStrings
55
EditText phone = (EditText)findViewById(R.id.phone);
!
if ((phone.getText() != null) && !phone.getText().equals("")) {
String phoneString = parsePhone(phone.getText().toString());
Intent intent = new Intent(Intent.ACTION_CALL,
Uri.parse("tel:" + phoneString));
startActivity(intent);
}

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Groovy Truth and GStrings
55
EditText phone = (EditText)findViewById(R.id.phone);
!
if ((phone.getText() != null) && !phone.getText().equals("")) {
String phoneString = parsePhone(phone.getText().toString());
Intent intent = new Intent(Intent.ACTION_CALL,
Uri.parse("tel:" + phoneString));
startActivity(intent);
}
EditText phone = findViewById(R.id.phone)
!
if (phone.text) {
def phoneString = parsePhone(phone.text)
def intent = new Intent(Intent.ACTION_CALL,
Uri.parse("tel:${phoneString}"))
startActivity intent
}

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Resource handling with closures and file methods
56
File f = new File("/sdcard/dir/f.txt");
if (f.exists() && f.canRead()) {
FileInputStream fis = null;
try {
fis = new FileInputStream(rFile);
byte[] bytes = new byte[fis.available()];
while (fis.read(bytes) != -1) {}
textView.setText(new String(bytes));
} catch (IOException e) {
// log and or handle
} finally {
if (fis != null) {
try {
fis.close();
// swallow
}
}
}
}

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56
try {
} finally {
if (fis != null) {
try {
fis.close();
// swallow
}
}
}
}
def f = new File("/sdcard/dir/f.txt")
f.withInputStream { fis ->
def bytes = new byte[fis.available()]
textView.text = new String(bytes)
}
}

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56
try {
} finally {
if (fis != null) {
try {
fis.close();
// swallow
}
}
}
}
f.withInputStream { fis ->
def bytes = new byte[fis.available()]
textView.text = new String(bytes)
}
}
textView.text = f.text
}

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What else?

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What else?
• Projects with dedicated Groovy support

!
• Swiss Knife
• similar to Butter Knife &  
Android Annotations

!
• Grooid Playground
• a builder for creating views 
in a hierarchical & visual manner
58

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Swiss Knife — Arasthel / SwissKnife
59

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Swiss Knife — Arasthel / SwissKnife
59
Like Butter Knife &
Android Annotations,
but for Groovy

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Swiss Knife
60
class MyActivity extends Activity {
!
@OnClick(R.id.button)
void onButtonClicked(Button button) {
Toast.makeText(this, "Clicked", Toast.LENGTH_SHOT).show()
}
!
@OnBackground
void doSomeProcessing(URL url) {
// Contents will be executed on background
}
!
@Override
setContentView R.layout.activity_main
SwissKnife.inject this
}
}

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Swiss Knife
60
!
}
!
@OnBackground
}
!
@Override
}
}
View
injection

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Swiss Knife
60
!
}
!
@OnBackground
}
!
@Override
}
}
Execute code outside
the UI thread

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Swiss Knife
60
!
}
!
@OnBackground
}
!
@Override
}
}
Injection point of views
and callbacks

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Swiss Knife — available annotations
!
• @OnUIThread

• @OnBackground

!
• @OnClick

• @OnLongClick

• @OnItemClick

• @OnItemLongClick

!
!
!
!
• @OnItemSelected

• @OnChecked

• @OnFocusChanged

• @OnTouch

• @OnPageChanged

• @OnTextChanged

• @OnEditorAction
61

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Swiss Knife — available annotations
!
• @OnUIThread

• @OnBackground

!
• @OnClick

• @OnLongClick

• @OnItemClick

• @OnItemLongClick

!
!
!
!
• @OnItemSelected

• @OnChecked

• @OnFocusChanged

• @OnTouch

• @OnPageChanged

• @OnTextChanged

• @OnEditorAction
61
AST transformations

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Swiss Knife — setup
62
dependencies {
…
compile 'com.arasthel:swissknife:1.0.4'
…
}

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Grooid Playground — karfunkel / grooid-playground
• When you need to build dynamic views (ie. not XML-driven)
63
def layout = new RelativeLayout(this)
layout.width = MATCH_PARENT
layout.height = MATCH_PARENT
layout.setPaddingRelative(64, 16, 64, 16)
!
def textView = new TextView(this)
textView.width = MATCH_PARENT
textView.height = 20
textView.setText R.string.hello_world
!
layout.addView textView
setContentView(layout)

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63
def layout = new RelativeLayout(this)
layout.width = MATCH_PARENT
layout.height = MATCH_PARENT
layout.setPaddingRelative(64, 16, 64, 16)
!
def textView = new TextView(this)
textView.width = MATCH_PARENT
textView.height = 20
textView.setText R.string.hello_world
!
layout.addView textView
setContentView(layout)
Imperative

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63
setContentView new AndroidBuilder().build(this) {
relativeLayout(width: MATCH_PARENT, height: MATCH_PARENT,
padding: [64.dip, 16.dip]) {
textView(width: MATCH_PARENT, height: 20.dip,
text: R.string.hello_world)
}
}
Declarative,
hierarchical,
visual

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Want more?

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Programming your Android applications in Groovy
• You can use Groovy to code Android apps!

• use Groovy 2.4.0-beta-1+ (latest: beta-3)

• prefer @CompileStatic

!
• Two great posts to get started:

• http://bit.ly/grooid-1

• http://bit.ly/grooid-2

!
• Gradle plugin support:

• http://bit.ly/grooid-gradle
65

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Demo conference application
66

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Demo conference application
66
Source code available:
http://bit.ly/grooid-app

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Demo Google Wear + Phone application
67

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Demo Google Wear + Phone application
67
Source code available:
http://bit.ly/grooid-wear

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Summary

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Summary
!
• Groovy can make your Android code…

• more concise & readable
• more maintainable
!
• Without compromising

• type safety
• speed
69

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Feedback welcome
70

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Feedback welcome
70
We need you
to help figure out
how Groovy
can help you!

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Q & A

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Image credits
• Stone age
• http://3.bp.blogspot.com/-lMDyyBdibG4/UxDYLq5ItiI/AAAAAAAALf8/HPpKRixHOIE/s1600/Neanderthal+Man+1.jpg
• Many thanks
• http://www.trys.ie/wp-content/uploads/2013/06/many-thanks.jpg
• Disclaimer
• http://3.bp.blogspot.com/-RGnBpjXTCQA/Tj2h_JsLigI/AAAAAAAABbg/AB5ZZYzuE5w/s1600/disclaimer.jpg
• Builders
• http://detroittraining.com/wp-content/uploads/Construction-Women2.jpg
• Newbie
• http://contently.com/strategist/wp-content/uploads/2014/05/bigstock-Shocked-Computer-Nerd-1520709.jpg
• Alternative rock band
• http://upload.wikimedia.org/wikipedia/commons/b/b2/Arcade_Fire_live_20050315.ext.jpg
• Twins
• http://images.doctissimo.fr/1/jumeaux-jumelles/photo/hd/4424027442/137540656da/jumeaux-jumelles-jumeaux-jumelles-2-big.jpg
• Annotations
• http://3.bp.blogspot.com/-f94n9BHko_s/T35ELs7nYvI/AAAAAAAAAKg/qe06LRPH9U4/s1600/IMG_1721.JPG
• Apple & Orange
• http://cdni.wired.co.uk/1920x1280/a_c/comparison.jpg
• We need you
• http://media.moddb.com/images/mods/1/14/13849/WickedSunshine_UncleSam_Blank_800x1000.png
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Image credits
• Macarons
• http://www.thatfoodcray.com/wp-content/uploads/2013/12/that-food-cray-pierre-herme-paris-hong-kong-christmas-flavors-foie-gras-
truffle-9.jpg?4dd047
• Bridge
• http://tenspeedhero.com/wp-content/uploads/Bridge_3.jpg
• Swiss knife
• http://www.formengifts.com/wp-content/uploads/2011/04/swiss-army-champ-multitool-knife2.jpg
• Hello World
• http://www.warrenpriestley.com/wp-content/uploads/2012/01/helloworld.gif
• George Clooney
• http://www.brewville.ca/wp-content/uploads/2014/05/nespresso-george-clooney.jpg
• Weight scale
• http://images.wisegeek.com/person-stands-on-scale.jpg
• Nexus 5
• http://fs01.androidpit.info/userfiles/2692059/image/Blog/nexus-5-weiss_628.jpg
• File icon
• https://dl.vecnet.org/assets/default.png
• Gear
• http://www.pvzgears.com/wp-content/uploads/2013/03/gears2a.png
• Sugar
• http://images.wisegeek.com/cane-sugar.jpg
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Groovy on Android -- DroidCon Paris 2014

Groovy on Android -- DroidCon Paris 2014

Guillaume Laforge

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