kotlin - lo swift di android

Kotlinlo Swift di Android

Good News Everyone!20 oct: Slide v1.1

3 oct: Slide v1.0

Omar MiatelloMember of GDG Milano (Italy)Android Developer @ Satispay

Personal profilegoogle.com/+OmarMiatelloGoogle+ Community: Kotlin for Androidgoo.gl/mUKF1wSlidesgoo.gl/7Vhy0s

http://google.com/+OmarMiatello

https://goo.gl/mUKF1w

https://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

http://kotlinlang.org/

http://kotlinlang.org/docs/reference/comparison-to-java.html

vspublic class MyKotlinClass { val a: Int = 1}

public class MyJavaClass { private final int a = 1;

public int getA() { return a; }}

#1 Kotlin - Properties: val, varhttp://kotlinlang.org/docs/reference/properties.html

http://kotlinlang.org/docs/reference/properties.html

public class MyKotlinClass { val a: Int = 1 var b: Int = 1}

public class MyJavaClass { private final int a = 1; private int b = 1;

public int getA() { return a; }

public int getB() { return b; }

public void setB(int b) { this.b = b; }}


vs


public class MyKotlinClass { val a: Int = 1 var b: Int = 1 val c = 1 var d = 1}

public class MyJavaClass { private final int a = 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 templateshttp://kotlinlang.org/docs/reference/basic-syntax.html#using-string-templates

vs

http://kotlinlang.org/docs/reference/basic-syntax.html#using-string-templates

class MyKotlinClass { 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 templateshttp://kotlinlang.org/docs/reference/basic-syntax.html#using-string-templates

vs

http://kotlinlang.org/docs/reference/basic-syntax.html#using-string-templates

class MyJavaClass { class MyItem { }

MyItem item;}

#3 Kotlin - Delegated Properties: lazy (as example)http://kotlinlang.org/docs/reference/delegated-properties.html

vs

http://kotlinlang.org/docs/reference/delegated-properties.html


MyItem item;

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


vs


class MyItem

class MyKotlinClass { val item by lazy { MyItem() }}

// Simplified: in Kotlin is synchronized


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 Casthttp://kotlinlang.org/docs/reference/typecasts.html#smart-casts

vs

http://kotlinlang.org/docs/reference/typecasts.html#smart-casts

class MyUtils {

static void example(View myView) { if (myView instanceof ImageView) { ImageView imageView = (ImageView) myView; } }

}


vs


class MyUtils {

static void example(View myView) { if (myView instanceof ImageView) { ImageView imageView = (ImageView) myView; imageView.setImageAlpha(10); } }

}


vs


class MyUtils {

static void example(View myView) { if (myView instanceof ImageView) { ImageView imageView = (ImageView) myView; imageView.setImageAlpha(10); } 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 {


}


vs


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

fun example2(myView: View) { when (myView) { is ImageView -> myView.imageAlpha = 10 is TextView -> myView.text = "Ciao" }}

class MyUtils {


}


vs

NEW EXAMPL

E


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 - Lambdashttp://kotlinlang.org/docs/reference/coding-conventions.html#lambdas

vs

http://kotlinlang.org/docs/reference/coding-conventions.html#lambdas

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 - Lambdashttp://kotlinlang.org/docs/reference/coding-conventions.html#lambdas

vs

http://kotlinlang.org/docs/reference/coding-conventions.html#lambdas

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 collectionshttp://kotlinlang.org/docs/reference/basic-syntax.html#using-collections

vs

NEW EXAMPL

E

http://kotlinlang.org/docs/reference/basic-syntax.html#using-collections


os.filterNotNull()

}

class MyUtils { static void example() { List<String> os = Arrays.asList("Android", "iOS", null, "Windows Phone"); List<String> osNotNull = new ArrayList<>(); for (String name : os) { if (name != null) osNotNull.add(name); } }}


vs

NEW EXAMPL

E



os.filterNotNull().sortedBy { it.length() }

}

class MyUtils { static void example() { List<String> os = Arrays.asList("Android", "iOS", null, "Windows Phone"); List<String> osNotNull = new ArrayList<>(); for (String name : os) { if (name != null) osNotNull.add(name); } Collections.sort(osNotNull, new Comparator<String>() { @Override public int compare(String l, String r) { return r.length() - l.length(); } }); }}


vs

NEW EXAMPL

E



os.filterNotNull().sortedBy { it.length() } .map { it.toUpperCase() }

}

class MyUtils { static void example() { List<String> os = Arrays.asList("Android", "iOS", null, "Windows Phone"); List<String> osNotNull = new ArrayList<>(); for (String name : os) { if (name != null) osNotNull.add(name); } Collections.sort(osNotNull, new Comparator<String>() { @Override public int compare(String l, String r) { return l.length() - r.length(); } }); for (String name : osNotNull) { String value = name.toUpperCase(); } }}


vs

NEW EXAMPL

E



os.filterNotNull().sortedBy { it.length() } .map { it.toUpperCase() } .forEach { print(it) }

}

class MyUtils { static void example() { List<String> os = Arrays.asList("Android", "iOS", null, "Windows Phone"); List<String> osNotNull = new ArrayList<>(); for (String name : os) { if (name != null) osNotNull.add(name); } Collections.sort(osNotNull, new Comparator<String>() { @Override public int compare(String l, String r) { return l.length() - r.length(); } }); for (String name : osNotNull) { String value = name.toUpperCase(); print(value); }} }


vs

NEW EXAMPL

E


fun String.isBig(): Boolean { return length() > 10}

#7 Kotlin - Extensionshttp://kotlinlang.org/docs/reference/extensions.html

vs

http://kotlinlang.org/docs/reference/extensions.html


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 Notationhttp://kotlinlang.org/docs/reference/functions.html#infix-notation

vs

http://kotlinlang.org/docs/reference/functions.html#infix-notation

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


vs



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



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 Overloadinghttp://kotlinlang.org/docs/reference/operator-overloading.html

vs

http://kotlinlang.org/docs/reference/operator-overloading.html

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


class MyKotlinClass { val a: String = "ciao" val b: String = null // Error at compile time}

#10 Kotlin - Null Safetyhttp://kotlinlang.org/docs/reference/null-safety.html

vs

http://kotlinlang.org/docs/reference/null-safety.html

class MyKotlinClass { val a: String = "ciao" val b: String = null // Error at compile time val c: String? = null val d: String? = "ok"}


vs


class MyKotlinClass { val a: String = "ciao" val b: String = null // Error at compile time val c: String? = null val d: String? = "ok"

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



fun example(e: String, f: String?) { e.length() f.length() // Error at compile time f?.length() }}

static class MyUtils { void example(String e, String f) { e.length(); // throw NullPointerException? f.length(); // throw NullPointerException? }}


vs



fun example(e: String, f: String?) { e.length() f.length() // Error at compile time f?.length()

if (f != null) { f.length() } }}

static class MyUtils { void example(String e, String f) { e.length(); // throw NullPointerException? f.length(); // throw NullPointerException?

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 Operatorhttp://kotlinlang.org/docs/reference/idioms.html#if-not-null-and-else-shorthand

vs

http://kotlinlang.org/docs/reference/idioms.html#if-not-null-and-else-shorthand

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); }

static void example() { String s = sound("fox"); String foxSay = s != null ? s : "No one knows";

}}

#11 Kotlin - Elvis Operatorhttp://kotlinlang.org/docs/reference/idioms.html#if-not-null-and-else-shorthand

vs

http://kotlinlang.org/docs/reference/idioms.html#if-not-null-and-else-shorthand

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.ktclass 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() }}

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

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

// ...

Preference Utils (Step 1) - MyActivity.javapublic class MyActivity extends AppCompatActivity {

private AppPreferences pref;

@Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); pref = new AppPreferences(this); }}



@Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); pref = new AppPreferences(this); String userName = pref.getUserName(); }}



@Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); pref = new AppPreferences(this); String userName = pref.getUserName();

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

Preference Utils (Step 2)Write a small utility for your Android app!

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

Preference Utils (Step 2) - MyActivity.javapublic class MyActivity extends BaseActivity {

@Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);

String userName = getPref().getUserName();

String userFavoriteAnimal = getPref().getUserFavoriteAnimal(); if (userFavoriteAnimal == null) { getPref().setUserFavoriteAnimal("fox"); } }}

Preference Utils (Step 3)Boost your Android app!

Preference Utils (Step 3) - MyActivity.ktpublic class MyActivity : BaseActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState)

val userName = pref.userName

val userFavoriteAnimal = pref.userFavoriteAnimal if (userFavoriteAnimal == null) { pref.userFavoriteAnimal = "fox" } }}

MyActivity.kt vs MyActivity.javapublic class MyActivity : BaseActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState)

val userName = pref.userName

val userFavoriteAnimal = pref.userFavoriteAnimal if (userFavoriteAnimal == null) { pref.userFavoriteAnimal = "fox" } }}

public class MyActivity extends BaseActivity {

@Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);

String userName = getPref().getUserName();

String userFavoriteAnimal = getPref().getUserFavoril(); if (userFavoriteAnimal == null) { getPref().setUserFavoriteAnimal("fox"); } }}

Play with animations!

Material Design: AnimationMeaningful transitions

Hierarchical timing

http://www.google.com/design/spec/animation/meaningful-transitions.html#meaningful-transitions-hierarchical-timing



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


fun calcDistance(x1: Int, y1: Int, x2: Int, y2: Int) = Math.sqrt(((x1-x2)*(x1-x2) + (y1-y2)*(y1-y2)).toDouble())


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?

http://kotlinlang.org/docs/events.html

THANKS!Omar Miatello, Member of GDG Milano (Italy)

Android Developer @ Satispay

kotlin - lo swift di android

Software