Android development kotlin

1. KOTLIN初體驗
andyang@TADSG

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

3. 有⼈人聽過
KOTLIN 嗎？

4. 有⼈人⽤用過
KOTLIN 嗎？

5. ⽂文字
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 ?!

6. ⽂文字
WHY KOTLIN
▸ Short Code
▸ Null Safety
▸ Smart Cast
▸ Lambda (Functional Programing)
▸ Method Extension
▸ Hybrid with Java
▸ Default final
▸ Everything is Object

7. ⽂文字
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’

8. ⽂文字
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

9. ⽂文字
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

10. ⽂文字
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

11. ⽂文字
DATA CLASS
▸ hashCode()
▸ toString()
▸ equals()
▸ with properties

12. ⽂文字
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)

13. ⽂文字
PROPERTIES
▸ val(value)
▸ val age (compile error)
▸ val age:Int (compile error)
▸ val age = 18 (ok)
▸ age = 19 (compile error)

14. ⽂文字
NULL SAFETY
▸ NullPointerException
▸ ? -> nullable, default non null
▸ var order : Order? = Order()
▸ order?.price (null safety if order is null)
▸ order.price (compile error)

15. ⽂文字
SMART CASE
▸ ClassCastException
▸ Stupid Case
if(exception instanceOf HttpException) {
HttpException httpException = (HttpException) exception
int code = httpException.getStatusCode();
}

16. ⽂文字
SMART CASE
▸ Smart Case
when(exception) {
is HttpException -> {
int code = exception.statusCode
}
default -> {
// do something else
}
}

17. ⽂文字
METHOD EXTENSION / INFIX
▸ Method Extension
var name : String = null
val isNull = name.isNullOrEmpty()
▸ In Java
if(name == null || name.length == 0)
StringUtils.isNullOrEmpty(name)

18. ⽂文字
METHOD EXTENSION / INFIX
▸ How
fun CharSequence?.isNullOrEmpty() : Boolean
= this == null || this.lenght == 0

19. ⽂文字
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”
)

20. ⽂文字
LAMBDA
▸ 不必再等 Java 8 到天荒地老
▸ 不⽤用 Retrolambda
▸ Kotlin 內建 lambda

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

22. ⽂文字
LAMBDA
▸ setOnClickListener()
view.setOnClickListener({ view ->
Toast.makeToast(…..).show()
})
view.setOnClickListener({
Toast.makeToast(…..).show()
})

23. ⽂文字
LAMBDA
▸ setOnClickListener()
view.setOnClickListener{ Toast.makeToast(…..).show()}
view.onClick{ Toast.makeToast(…..).show()}

24. ⽂文字
LAMBDA
▸ Adapter OnItemClickListener
interface OnOrderItemClickListener{
onOrderItemClick(Order order);
}
OnOrderItemClickListener onOrderItemClickListener;
‣ interface, setter, init, invoke

25. ⽂文字
LAMBDA
▸ Adapter OnItemClickListener in Kotlin
var onOrderItemClickListener : (order: Order) -> Unit
holder?.onClick{
onOrderItemClickListener.invoke(order)
}
holder?.onClick{
onOrderItemClickListener(order)
}

26. ⽂文字
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)

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

28. ⽂文字
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()

29. ⽂文字
PROPERTISE DELEGATE
‣ Demo Delegate SharedPreferences

30. ⽂文字
DEPENDENCY INJECTION
‣ In MPV Pattern
‣ Presenter need inject Model
‣ Repository(NetworkService networkService,
LocalData localData)
‣ LocalData(Content context)
‣ Presenter(View view, Repository repository)

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

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

33. ⽂文字
DEPENDENCY INJECTION
‣ In kotlin
‣ val presenter = Presenter(view)
‣ for testing
‣ val presenter = Presenter(view, mockRepository)

34. ⽂文字
REFERENCE
▸ Kotlin official guide
▸ https://kotlinlang.org/docs/reference/
▸ Kotlin For Android Developer (e-book)
▸ https://antonioleiva.com/kotlin-android-developers-
book/

35. 學習⼀一⾨門語⾔言最快的
⽅方式就是只能⽤用它！
andyang
⽂字

36. Ｑ＆Ａ