KOTLINandyang@TADSG

ABOUT ME

Andy

@

@ Android Developer (TADSG)

@ Android Code Club ()

KOTLIN

KOTLIN

HELLO KOTLIN

JetBrains JVM

Effective Java

Java ?!

WHY KOTLIN

Short Code

Null Safety

Smart Cast

Lambda (Functional Programing)

Method Extension

Hybrid with Java

Default final

Everything is Object

HOW KOTLIN

Install Android Studio Plugin Kotlin

cmd + shift + a -> Configure kotlin in Project

classpth : org.jetbrains.kotlin:lotlin-gradle-plugin:1.0.7

apply plugin: kotlin-android

compile org.jetbrains.kotlin:kotlin-stdlib:1.0.7

JAVA TO KOTLIN

kotlin

cmd + shift + a -> Convert Java File to Kotlin

KOTLIN FEATURE Multiple class in one file

Data Class

Properties val/var

Null Safety

Smart Cast

Method Extension / infix

Lambda

Operator Overloading

Companion object

Delegate

Dependency Injection

MULTIPLE CLASS IN ONE FILE

Class

Class

DATA CLASS

hashCode()

toString()

equals()

with properties

PROPERTIES

var(variable)

var age (compile error)

var age:Int (compile error)

var age = 1 (ok)

age = 2 (ok)

age = null (ok)

var myAge = age (ok)

PROPERTIES

val(value)

val age (compile error)

val age:Int (compile error)

val age = 18 (ok)

age = 19 (compile error)

NULL SAFETY

NullPointerException

? -> nullable, default non null

var order : Order? = Order()

order?.price (null safety if order is null)

order.price (compile error)

SMART CASE

ClassCastException

Stupid Case

if(exception instanceOf HttpException) {

HttpException httpException = (HttpException) exception

int code = httpException.getStatusCode();

}

SMART CASE Smart Case

when(exception) {

is HttpException -> {

int code = exception.statusCode

}

default -> {

// do something else

}

}

METHOD EXTENSION / INFIX

Method Extension

var name : String = null

val isNull = name.isNullOrEmpty()

In Java

if(name == null || name.length == 0)

StringUtils.isNullOrEmpty(name)

METHOD EXTENSION / INFIX

How

fun CharSequence?.isNullOrEmpty() : Boolean

= this == null || this.lenght == 0

METHOD EXTENSION / INFIX Infix

val isLike = ABC like 123-ABC

infix fun String.like(it: String) : Boolean =

this.toUpperCase.contains(it)

name to Andy

mapOf(

Pair(nickName, andyang),

name to Andy

)

LAMBDA

Java 8

Retrolambda

Kotlin lambda

LAMBDA

setOnClickListener()

view.setOnClickListener(new OnClickListener(){

@Override

public void onClick(View v){

Toast.makeToast(..).show()

}

})

LAMBDA

setOnClickListener()

view.setOnClickListener({ view ->

Toast.makeToast(..).show()

})

view.setOnClickListener({

Toast.makeToast(..).show()

})

LAMBDA

setOnClickListener()

view.setOnClickListener{ Toast.makeToast(..).show()}

view.onClick{ Toast.makeToast(..).show()}

LAMBDA

Adapter OnItemClickListener

interface OnOrderItemClickListener{

onOrderItemClick(Order order);

}

OnOrderItemClickListener onOrderItemClickListener;

interface, setter, init, invoke

LAMBDA

Adapter OnItemClickListener in Kotlin

var onOrderItemClickListener : (order: Order) -> Unit

holder?.onClick{

onOrderItemClickListener.invoke(order)

}

holder?.onClick{

onOrderItemClickListener(order)

}

OPERATOR OVERLOADING

a == b -> a.equals(b)

a + b -> a.plus(b)

a - b, a * b, a / b, a % b ..

a..b -> a.rangeTo(b)

a in b -> a.contains(b)

a[i] -> a.get(i)

a[i] = b -> a.set(i, b)

COMPANION OBJECTclass App : Application() {

companion object {

private var instance: Application? = null

fun instance() = instance

}

override fun onCreate() {

super.onCreate();

instance = this

}

}

PROPERTISE DELEGATEclass Delegate : ReadWriteProperty {

override fun getValue(thisRef: Any?, property : KPropety) {

}

override fun setValue(thisRef: Any?, property : KPropety, value: T) {

}

}

var name : String by Delegate()

PROPERTISE DELEGATE Demo Delegate SharedPreferences

DEPENDENCY INJECTION In MPV Pattern

Presenter need inject Model

Repository(NetworkService networkService, LocalData localData)

LocalData(Content context)

Presenter(View view, Repository repository)

DEPENDENCY INJECTION new Presenter

In Java

Presenter presenter = new Presenter(new Repository(new NetworkService(), new LocalData(context))); // so ugly

Presenter presenter = PresenterFactory.create();

DEPENDENCY INJECTION In kotlin

Repository(networkService : NetworkService = NetworkService(), localData : LocalData = LocalData())

LocalData(context : Content = App.instance())

Presenter(view : View, repository : Repository = Repository())

DEPENDENCY INJECTION In kotlin

val presenter = Presenter(view)

for testing

val presenter = Presenter(view, mockRepository)

REFERENCE

Kotlin official guide

https://kotlinlang.org/docs/reference/

Kotlin For Android Developer (e-book)

https://antonioleiva.com/kotlin-android-developers-book/

https://kotlinlang.org/docs/reference/https://antonioleiva.com/kotlin-android-developers-book/https://antonioleiva.com/kotlin-android-developers-book/

andyang