Kotlin: lo Swift di Android (2015)

Kotlin
lo Swift di Android
Good News Everyone!
20 oct: Slide v1.1
3 oct: Slide v1.0

Omar Miatello
Member of GDG Milano (Italy)
Android Developer @ Satispay
Personal profile
google.com/+OmarMiatello
Google+ Community: Kotlin for Android
goo.gl/mUKF1w
Slides
goo.gl/7Vhy0s

What is Kotlin?
Statically typed programming language for the JVM, Android and the browser.
(http://kotlinlang.org/)
Why Kotlin?
● Concise: drastically reduce the amount of boilerplate code you need to write.
● Safe: avoid entire classes of errors such as null pointer exceptions.
● Interoperable: leverage existing frameworks and libraries of the JVM with 100% Java
Interoperability.
and more... http://kotlinlang.org/docs/reference/comparison-to-java.html

vs
public class MyKotlinClass {
val a: Int = 1
}
public class MyJavaClass {
private final int a = 1;
public int getA() {
return a;
}
}
#1 Kotlin - Properties: val, var
http://kotlinlang.org/docs/reference/properties.html

val a: Int = 1
var b: Int = 1
}
private int b = 1;
public int getA() {
return a;
}
public int getB() {
return b;
}
public void setB(int b) {
this.b = b;
}
}
vs

val a: Int = 1
var b: Int = 1
val c = 1
var d = 1
}
private int b = 1;
private final int c = 1;
private int d = 1;
public int getA() { return a; }
public int getB() { return b; }
public void setB(int b) { this.b = b; }
public int getC() { return c; }
public int getD() { return d; }
public void setD(int d) { this.d = d; }
}
vs

class MyKotlinClass {
val name = "Omar"
val surname = "Miatello"
}
class MyJavaClass {
final String getName() {
return "Omar";
}
final String getSurname() {
return "Miatello";
}
}
#2 Kotlin - String templates
http://kotlinlang.org/docs/reference/basic-syntax.html#using-string-templates
vs

val name = "Omar"
val surname = "Miatello"
val example = "My name is $name $surname"
}
class MyJavaClass {
final String getName() {
return "Omar";
}
final String getSurname() {
return "Miatello";
}
final String getExample() {
return String.format("My name is %s %s",
getName(), getSurname()); }
}
#2 Kotlin - String templates
http://kotlinlang.org/docs/reference/basic-syntax.html#using-string-templates
vs

class MyJavaClass {
class MyItem { }
MyItem item;
}
#3 Kotlin - Delegated Properties: lazy (as example)
http://kotlinlang.org/docs/reference/delegated-properties.html
vs

class MyJavaClass {
class MyItem { }
MyItem item;
final MyItem getItem() {
if (item == null) {
item = new MyItem();
}
return item;
}
}
vs

class MyItem
val item by lazy { MyItem() }
}
// Simplified: in Kotlin is synchronized
class MyJavaClass {
class MyItem { }
MyItem item;
final MyItem getItem() {
if (item == null) {
item = new MyItem();
}
return item;
}
}
vs

class MyUtils {
static void example(View myView) {
if (myView instanceof ImageView) {
}
}
}
#4 Kotlin - Smart Cast
http://kotlinlang.org/docs/reference/typecasts.html#smart-casts
vs

class MyUtils {
ImageView imageView =
(ImageView) myView;
}
}
}
vs

class MyUtils {
(ImageView) myView;
imageView.setImageAlpha(10);
}
}
}
vs

class MyUtils {
(ImageView) myView;
} else if (myView instanceof TextView) {
TextView textView = (TextView) myView;
textView.setText("Ciao");
}
}
}
vs

fun example1(myView: View) {
if (myView is ImageView) {
myView.setImageAlpha(10)
} else if (myView is TextView) {
myView.setText("Ciao")
}
}
class MyUtils {
(ImageView) myView;
}
}
}
vs

if (myView is ImageView) {
myView.setImageAlpha(10)
} else if (myView is TextView) {
myView.setText("Ciao")
}
}
when (myView) {
is ImageView -> myView.imageAlpha = 10
is TextView -> myView.text = "Ciao"
}
}
class MyUtils {
(ImageView) myView;
}
}
}
vs
NEW
EXAMPLE

class MyActivity : Activity() {
fun example() {
val view = findViewById(R.id.button)
view.setOnClickListener {
}
}
}
class MyActivity extends Activity {
void example() {
View view = findViewById(R.id.button);
view.setOnClickListener(
);
}
}
#5 Kotlin - Lambdas
http://kotlinlang.org/docs/reference/coding-conventions.html#lambdas
vs

class MyActivity : Activity() {
fun example() {
val view = findViewById(R.id.button)
view.setOnClickListener {
Log.d("TAG", "Item clicked!")
}
}
}
class MyActivity extends Activity {
void example() {
View view = findViewById(R.id.button);
view.setOnClickListener(
new View.OnClickListener() {
@Override
public void onClick(View v) {
Log.d("TAG", "Item clicked!");
}
}
);
}
}
#5 Kotlin - Lambdas
http://kotlinlang.org/docs/reference/coding-conventions.html#lambdas
vs

fun example() {
val os = listOf("Android", "iOS", null,
"Windows Phone")
}
class MyUtils {
static void example() {
List<String> os = Arrays.asList("Android",
"iOS", null, "Windows Phone");
}
}
#6 Kotlin - Using collections
http://kotlinlang.org/docs/reference/basic-syntax.html#using-collections
vs
NEW
EXAMPLE

fun example() {
"Windows Phone")
os.filterNotNull()
}
class MyUtils {
List<String> osNotNull = new ArrayList<>();
for (String name : os) {
if (name != null) osNotNull.add(name);
}
}
}
vs
NEW
EXAMPLE

fun example() {
"Windows Phone")
os.filterNotNull().sortedBy { it.length() }
}
class MyUtils {
}
Collections.sort(osNotNull, new
Comparator<String>() { @Override
public int compare(String l, String r) {
return r.length() - l.length();
}
});
}
}
vs
NEW
EXAMPLE

fun example() {
"Windows Phone")
.map { it.toUpperCase() }
}
class MyUtils {
}
return l.length() - r.length();
}
});
for (String name : osNotNull) {
String value = name.toUpperCase();
}
}
}
vs
NEW
EXAMPLE

fun example() {
"Windows Phone")
.map { it.toUpperCase() }
.forEach { print(it) }
}
class MyUtils {
}
return l.length() - r.length();
}
});
for (String name : osNotNull) {
String value = name.toUpperCase();
print(value);
}
} }
vs
NEW
EXAMPLE

fun String.isBig(): Boolean {
return length() > 10
}
#7 Kotlin - Extensions
http://kotlinlang.org/docs/reference/extensions.html
vs

}
fun example() {
"why?!".isBig() // false!
"harder, better, ...".isBig() // true!
}
vs

}
fun example() {
"why?!".isBig() // false!
"harder, better, ...".isBig() // true!
}
// file MyUtils.java
class MyUtils {
static boolean isBig(String str) {
return str.length() > 10;
}
}
// file MyJavaClass.java
class MyJavaClass {
void example() {
MyUtils.isBig("why?!");
MyUtils.isBig("harder, better, ...");
}
}
vs

}
fun example() {
"why?!".isBig()
"harder, better, ...".isBig()
}
// file MyUtils.java
class MyUtils {
static boolean isBig(String str) {
return str.length() > 10;
}
}
// file MyJavaClass.java
class MyJavaClass {
void example() {
MyUtils.isBig("why?!");
MyUtils.isBig("harder, better, ...");
}
}
vs

class Hero(val power: Int) class Hero {
private final int power;
public Hero(int power) {
this.power = power;
}
}
#8 Kotlin - Infix Notation
http://kotlinlang.org/docs/reference/functions.html#infix-notation
vs

class Hero(val power: Int) {
fun vs(opponent: Hero): Hero {
return if (power > opponent.power) {
this
} else {
opponent
}
}
}
vs

this
} else {
opponent
}
}
}
fun example() {
val thor = Hero(7)
val ironman = Hero(8)
val spiderman = Hero(4)
}
// Skip Java version of Hero class,
// we use Kotlin class
class MyJavaClass {
void example() {
Hero thor = new Hero(7);
Hero ironman = new Hero(8);
Hero spiderman = new Hero(4);
}
}
vs

this
} else {
opponent
}
}
}
fun example() {
val thor = Hero(7)
val ironman = Hero(8)
val spiderman = Hero(4)
val theBest = thor vs ironman vs spiderman
}
// Skip Java version of Hero class,
// we use Kotlin class
class MyJavaClass {
void example() {
Hero thor = new Hero(7);
Hero ironman = new Hero(8);
Hero spiderman = new Hero(4);
Hero theBest =
thor.vs(ironman).vs(spiderman);
}
}
vs

class Male(val eyes: String)
class Female(val hair: String)
class Male {
private String eyes;
public Male(String eyes) {
this.eyes = eyes;
}
}
class Female {
private String hair;
public Female(String hair) {
this.hair = hair;
}
}
#9 Kotlin - Operator Overloading
http://kotlinlang.org/docs/reference/operator-overloading.html
vs

class Male(val eyes: String)
class Baby(val eyes: String, val hair: String)
// Skip Java version of Male, Female and Baby
// class, there is not enough space!
vs

class Male(val eyes: String) {
fun plus(her: Female): Baby {
return Baby(this.eyes, her.hair)
}
}
vs

}
}
fun example() {
val myBaby = Male("green") + Female("blond")
}
class MyJavaClass {
void example() {
Baby myBaby = new Male("green").plus(
new Female("blond"));
}
}
vs

}
}
fun example() {
val myBaby = Male("green") + Female("blond")
}
class MyJavaClass {
void example() {
Baby myBaby =
new Male("green").plus(new Female("blond"));
}
}
vs

val a: String = "ciao"
val b: String = null // Error at compile time
}
#10 Kotlin - Null Safety
http://kotlinlang.org/docs/reference/null-safety.html
vs

val c: String? = null
val d: String? = "ok"
}
vs

fun example(e: String, f: String?) {
e.length()
f.length() // Error at compile time
}
}
static class MyUtils {
void example(String e, String f) {
e.length(); // throw NullPointerException?
f.length(); // throw NullPointerException?
}
}
vs

e.length()
f?.length()
}
}
}
}
vs

e.length()
f?.length()
if (f != null) {
f.length()
}
}
}
if (e != null) {
e.length();
}
if (f != null) {
e.length();
}
}
}
vs

val map = mapOf(
"dog" to "woof",
"cat" to "meow",
"bird" to "tweet",
"mouse" to "squeek")
fun sound(animal: String): String? {
return map.get(animal)
}
class MyUtils {
static Map<String, String> map = // ...
static String sound(String animal) {
return map.get(animal);
}
}
#11 Kotlin - Elvis Operator
http://kotlinlang.org/docs/reference/idioms.html#if-not-null-and-else-shorthand
vs

val map = mapOf(
"dog" to "woof",
"cat" to "meow",
"bird" to "tweet",
"mouse" to "squeek")
fun sound(animal: String): String? {
return map.get(animal)
}
fun example() {
val foxSay = sound("fox") ?: "No one knows"
}
class MyUtils {
static Map<String, String> map = // ...
static String sound(String animal) {
return map.get(animal);
}
String s = sound("fox");
String foxSay =
s != null ? s : "No one knows";
}
}
#11 Kotlin - Elvis Operator
http://kotlinlang.org/docs/reference/idioms.html#if-not-null-and-else-shorthand
vs

1. Open “Preferences”
Install Kotlin in Android Studio

2. Choose “Plugins” and “Install
JetBrains plugin…”

3. Install “Kotlin” and “Kotlin
Extensions For Android”

4. Restart Android Studio, and
open (or create) a project

5. Create a new “Kotlin class”

6. Choose from menu “Tools” >
“Kotlin” > “Configure Kotlin in
Project”

6. Choose from menu “Tools” >
“Kotlin” > “Configure Kotlin in
Project”
7. Ready for Kotlin! :)
dependencies {
// other dependencies ...
compile "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
}
buildscript {
ext.kotlin_version = '0.13.1514'
repositories {
mavenCentral()
}
dependencies {
classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
}
}
repositories {
mavenCentral()
}

Preference Utils (Step 1)
Write a small utility for Android!

Preference Utils (Step 1) - PreferenceUtils.kt
class AppPreferences(private val context: Context) {
val preferences: SharedPreferences = PreferenceManager.getDefaultSharedPreferences(context)
}

}
object PreferenceDelegates {
public fun string(defaultValue: String? = null): ReadWriteProperty<AppPreferences, String?> {
return PrefString(defaultValue)
}
}

}
object PreferenceDelegates {
public fun string(defaultValue: String? = null): ReadWriteProperty<AppPreferences, String?> {
return PrefString(defaultValue)
}
}
private class PrefString(private val defaultValue: String?) : ReadWriteProperty<AppPreferences, String?> {
override fun get(thisRef: AppPreferences, property: PropertyMetadata): String? {
return thisRef.preferences.getString(property.name, defaultValue)
}
override fun set(thisRef: AppPreferences, property: PropertyMetadata, value: String?) {
thisRef.preferences.edit().putString(property.name, value).apply()
}
}

var userName by PreferenceDelegates.string()
var userFavoriteAnimal by PreferenceDelegates.string()
}
// ...

Preference Utils (Step 1) - MyActivity.java
public class MyActivity extends AppCompatActivity {
private AppPreferences pref;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
pref = new AppPreferences(this);
}
}

@Override
String userName = pref.getUserName();
}
}

@Override
String userName = pref.getUserName();
String userFavoriteAnimal = pref.getUserFavoriteAnimal();
if (userFavoriteAnimal == null) {
pref.setUserFavoriteAnimal("fox");
}
}
}

Write a small utility for your Android app!

Preference Utils (Step 2) - App.kt
class App : Application() {
val pref by lazy { AppPreferences(this) }
override fun onCreate() {
super.onCreate()
// other initialization here
}
}

Preference Utils (Step 2) - AndroidManifest.xml
<manifest xmlns:android="http://schemas.android.com/apk/res/android">
<application
android:name=".application.App"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name" >
<activity android:name=".MyActivity" />
</application>
</manifest>

Preference Utils (Step 2) - BaseActivity.kt
open class BaseActivity : AppCompatActivity() {
val app by lazy { application as App }
val pref by lazy { app.pref }
}

public class MyActivity extends BaseActivity {
@Override
String userName = getPref().getUserName();
String userFavoriteAnimal = getPref().getUserFavoriteAnimal();
getPref().setUserFavoriteAnimal("fox");
}
}
}

Boost your Android app!

Preference Utils (Step 3) - MyActivity.kt
public class MyActivity : BaseActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
val userName = pref.userName
val userFavoriteAnimal = pref.userFavoriteAnimal
pref.userFavoriteAnimal = "fox"
}
}
}

MyActivity.kt vs MyActivity.java
public class MyActivity : BaseActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
val userName = pref.userName
val userFavoriteAnimal = pref.userFavoriteAnimal
pref.userFavoriteAnimal = "fox"
}
}
}
public class MyActivity extends BaseActivity {
@Override
String userName = getPref().getUserName();
String userFavoriteAnimal =
getPref().getUserFavoril();
getPref().setUserFavoriteAnimal("fox");
}
}
}

Play with
animations!
Material Design: Animation
Meaningful transitions
Hierarchical timing

Play with animations! - AnimationUtils.java
fun View.animateAppear() {
alpha = 0f
scaleX = 0f
scaleY = 0f
val animator = ViewCompat.animate(this).alpha(1f).scaleX(1f).scaleY(1f)
animator.start()
}

alpha = 0f
scaleX = 0f
scaleY = 0f
animator.start()
}
fun calcDistance(x1: Int, y1: Int, x2: Int, y2: Int) = Math.sqrt(((x1-x2)*(x1-x2) + (y1-y2)*(y1-y2)).toDouble())

alpha = 0f
scaleX = 0f
scaleY = 0f
animator.start()
}
fun calcDistance(x1: Int, y1: Int, x2: Int, y2: Int) = Math.sqrt(((x1-x2)*(x1-x2) + (y1-y2)*(y1-y2)).toDouble())
fun List<View>.animateRelativeHierarchicalTiming(centerX: Int = 0, centerY: Int = 0) {
forEach {
val x = it.left
val y = it.top
val distance = calcDistance(centerX, centerY, x, y)
it.postDelayed({ it.animateAppear() }, distance.toLong())
}
}

Upcoming Events
JavaLand 2016 | Kotlin in Action (Justin Lee)
Codemotion 2015 | Kotlin for Android Developers (Antonio Leiva Gordillo)
Oredev | Advancing Android Development with the Kotlin Language (Jake Wharton)
dotnetconf 2015 | Kotlin in Production. Why? How? (Kirill Bubochkin)
DroidCon London 2015 | Advancing Development with the Kotlin Language (Jake Wharton)
JavaOne 2015 | Kotlin in Anger (Justin Lee)
JavaOne 2015 | Type Inference in Kotlin (Svetlana Isakova)
JOKER | The Experience of Using Kotlin in JetBrains (Dmitry Jemerov)
Mobilization 2015 | Kotlin for Android (Paweł Gajda)
DevFest 2015 | Kotlin: lo Swift di Android (Omar Miatello)
http://kotlinlang.org/docs/events.html
Questions?

THANKS!
Omar Miatello, Member of GDG Milano (Italy)
Android Developer @ Satispay

Kotlin: lo Swift di Android (2015)

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