Kotlin初體驗

KOTLIN初體驗
andyang@AndroidTaipei
@2017 PKLOT CO., LTD

ABOUT ME
▸ Andy
▸ @ 停⾞車車⼤大聲公
▸ @ Android Developer 讀書會 (TADSG)
▸ @ Android Code Club (週三晚上)

有⼈人聽過 KOTLIN 嗎？

有⼈人⽤用過 KOTLIN 嗎？

HELLO KOTLIN
▸ JetBrains 開發的 JVM 語⾔言
▸ 包含很多 Eﬀective Java 的思想在裡⾯面
▸ Java 開發者的夢幻語⾔言 ?!

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
▸ 遇到不知道如何表達的 kotlin 語法可以先透過轉換觀察
▸ cmd + shift + a -> Convert Java File to Kotlin
▸ ⼀一鍵完成

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 的整理理更更有彈性
▸ 同質性⾼高且簡易易的 Class 可以放到⼀一起
▸ 提⾼高閱讀，不易易中斷思考

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)

▸ How
fun CharSequence?.isNullOrEmpty() : Boolean
= this == null || this.lenght == 0

▸ 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
▸ 不必再等 Java 8 到天荒地老
▸ 不⽤用 Retrolambda
▸ Kotlin 內建 lambda

LAMBDA
▸ setOnClickListener()
view.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View v){
Toast.makeToast(…..).show()
}
})

LAMBDA
view.setOnClickListener({ view ->
})
view.setOnClickListener({
})

LAMBDA
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 OBJECT
class App : Application() {
companion object {
private var instance: Application? = null
fun instance() = instance
}
override fun onCreate() {
super.onCreate();
instance = this
}
}

PROPERTISE DELEGATE
class Delegate<T> : ReadWriteProperty<Any?, T> {
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)

‣ new Presenter
‣ In Java
Presenter presenter = new Presenter(new Repository(new
NetworkService(), new LocalData(context))); // so ugly
Presenter presenter = PresenterFactory.create();

‣ In kotlin
‣ Repository(networkService : NetworkService = NetworkService(),
localData : LocalData = LocalData())
‣ LocalData(context : Content = App.instance())
‣ Presenter(view : View, repository : Repository = Repository())

‣ 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/

學習⼀一⾨門語⾔言最快的⽅方式就是只能⽤用它！

Q&A

停車大聲公
總是給你更好的停車體驗

Kotlin初體驗

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