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

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

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

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; }}

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

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; }}

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

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

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

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

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; }}

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

vs

class MyItem

class MyKotlinClass { 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; }}

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

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

class MyUtils {

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

}

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

vs

class MyUtils {

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

}

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

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"); } }

}

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

vs

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

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"); } }

}

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

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 {

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"); } }

}

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

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

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

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

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

fun example() { val os = listOf("Android", "iOS", null, "Windows Phone")

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); } }}

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

vs

NEW EXAMPL

E

fun example() { val os = listOf("Android", "iOS", null, "Windows Phone")

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(); } }); }}

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

vs

NEW EXAMPL

E

fun example() { val os = listOf("Android", "iOS", null, "Windows Phone")

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(); } }}

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

vs

NEW EXAMPL

E

fun example() { val os = listOf("Android", "iOS", null, "Windows Phone")

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); }} }

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

vs

NEW EXAMPL

E

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

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

vs

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

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

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

vs

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

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, ..."); }}

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

vs

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

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, ..."); }}

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

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

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

#8 Kotlin - Infix Notationhttp://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 } }}

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); }}

#8 Kotlin - Infix Notationhttp://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 } }}

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); }}

#8 Kotlin - Infix Notationhttp://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 } }}

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); }}

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

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

class Male(val eyes: String)

class Female(val hair: String)

class Baby(val eyes: String, val hair: String)

// Skip Java version of Male, Female and Baby// class, there is not enough space!

#9 Kotlin - Operator Overloadinghttp://kotlinlang.org/docs/reference/operator-overloading.html

vs

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

class Female(val hair: String)

class Baby(val eyes: String, val hair: String)

// Skip Java version of Male, Female and Baby// class, there is not enough space!

#9 Kotlin - Operator Overloadinghttp://kotlinlang.org/docs/reference/operator-overloading.html

vs

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

class Female(val hair: String)

class Baby(val eyes: String, val hair: String)

fun example() { val myBaby = Male("green") + Female("blond")}

// Skip Java version of Male, Female and Baby// class, there is not enough space!

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

#9 Kotlin - Operator Overloadinghttp://kotlinlang.org/docs/reference/operator-overloading.html

vs

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

class Female(val hair: String)

class Baby(val eyes: String, val hair: String)

fun example() { val myBaby = Male("green") + Female("blond")}

// Skip Java version of Male, Female and Baby// class, there is not enough space!

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

#9 Kotlin - Operator Overloadinghttp://kotlinlang.org/docs/reference/operator-overloading.html

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

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

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

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? }}

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

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 f?.length() }}

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

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

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 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(); } }}

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

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

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

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

1. Open “Preferences”

Install Kotlin in Android Studio

1. Open “Preferences”

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

Install Kotlin in Android Studio

1. Open “Preferences”

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

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

Install Kotlin in Android Studio

1. Open “Preferences”

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

Install Kotlin in Android Studio

1. Open “Preferences”

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”

Install Kotlin in Android Studio

1. Open “Preferences”

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”

Install Kotlin in Android Studio

1. Open “Preferences”

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”

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()}

Install Kotlin in Android Studio

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)}

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) }}

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) }}

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)}

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)}

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); }}

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

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); 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) - 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) - 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

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()}

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())

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 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()) }}

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 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()) }}

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Questions?

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

Android Developer @ Satispay