Vamos falar sobre Kotlin, que recentemente foi divulgada no Google IO 2017 como a linguagem oficial para Android. O objetivo será mostrar algumas características da linguagem e como aplica-las no Android.

1. Kotlin
A nova linguagem oficial do Android

2. GDGFoz
Quem ?
• Houssan Ali Hijazi - hussanhijazi@gmail.com
• Desenvolvedor Android na www.HElabs.com
• Organizador GDG Foz do Iguaçu
• www.lojasnoparaguai.com.br
• www.desaparecidosbr.org
• www.hussan.com.br

3. GDGFoz
Kotlin
• 2011/JetBrains
• 1.0 em Fev. 2016
• 1.1 em Mar. 2017
• Pinterest, Coursera, Netflix, Uber, Square, Trello e
Basecamp
• Google IO 2017

4. GDGFoz
Kotlin

5. GDGFoz
Kotlin
• Interoperabilidade
• Null Safety
• Conciso

6. GDGFoz
Properties/Fields
val name: String = "João"
val name = "João"

7. GDGFoz
val/var
val user = User()
user = User() // :(
var user = User()
user = User() // :)

8. GDGFoz
Null Safety/Safe Calls
var name: String? = "José"
println(name?.length)
var name: String = "José"
name = null // :(
var name: String? = "José"
name = null // :)
val lastName: String? = null

9. GDGFoz
Elvis Operator
val name: String? = "José"
val c: Int = if (name != null) name.length else -1
val c = name?.length ?: -1

10. GDGFoz
Class
class Car(val name: String = ""): Vehicle() {
constructor(name: String, color: String) : this(name) {
}
}

11. GDGFoz
Kotlin
class Car
{
private String name;
public String getName()
{
//...
}
public void setName(String s)
{
//...
}
}
// ^^Java
// vv Kotlin
val car = Car()
println("Name: ${car.name}")

12. GDGFoz
Functions
fun calculate(num: Int, num2: Int = 10): Int
{
return num + num2
}
fun calculate(num: Int, num2: Int): Int
= num + num2
fun calculate(num: Int, num2: Int)
= num + num2
calculate(num = 10, num2 = 20)

13. GDGFoz
Interface
interface BaseView {
fun bar()
fun foo() {
// optional body
}
}
class View : BaseView {
override fun bar() {
}
}

14. GDGFoz
Data Class
data class Truck(val name:String, val color: String
= "Red")

15. GDGFoz
For/Range
// prints number from 1 through 10
for (i in 1..10) {
print(i)
}
// prints 100, 98, 96 ...
for (i in 100 downTo 1 step 2) {
print(i)
}
for (item in collection) print(item)

16. GDGFoz
When
when (x) {
in 1..10 -> print("x is in the range")
!in 10..20 -> print("x is outside the range")
else -> print("none of the above")
}
fun hasPrefix(x: Any) = when(x) {
is String -> x.startsWith("prefix")
else -> false
}
when (x) {
1 -> print("x == 1")
2 -> print("x == 2")
else -> {
print("x is neither 1 nor 2")
}
}

17. GDGFoz
Collections
val set = hashSetOf(1, 2, 3)
val list = arrayListOf(1, 2, 3)
val items = listOf(1, 2, 3, 4)
items.first() == 1
items.last() == 4
items.filter { it % 2 == 0 } // returns [2, 4]
items.forEach { println(it) }
// count, forEachIndexed, max, min, take, slice, map, flatMap
… etc..
// More in https://antonioleiva.com/collection-operations-
kotlin/

18. GDGFoz
Lambdas
showButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View button) {
text.setVisibility(View.VISIBLE)
button.setBackgroundColor(ContextCompat.getColor(this,
R.color.colorAccent))
}
});
// ^^ Java
showButton.setOnClickListener { button ->
text.visibility = View.VISIBLE
button.setBackgroundColor(ContextCompat.getColor(thi
s, R.color.colorAccent))
}
// ^^Kotlin

19. GDGFoz
Lambdas
// ^^ Class
validate(this::toast)
fun validate(callback: () -> Unit)
{
// validate
callback.invoke()
}
fun toast() {
val toast = Toast.makeText(this, "Callback called",
Toast.LENGTH_LONG)
toast.show()
}

20. GDGFoz
let/with
var name: String? = "João"
name?.let {
println(it.toUpperCase())
println(it.length)
}
with(name) {
println(toUpperCase())
println(length)
}
// See: apply/run

21. GDGFoz
Infix
infix fun String.drive(car: String) =
Pair(this, car)
val usersCars = mapOf("José" drive "Fusca",
"João" drive "Ferrari")
val usersCars2 =
mapOf("José".drive("Fusca"),
"João".drive("Ferrari"));
val (driver, car) = "José" drive "Fusca"

22. GDGFoz
Extensions
fun View.hide()
{
visibility = View.GONE
}
fun View.show()
{
visibility = View.VISIBLE
}
button.setVisibility(View.VISIBLE)
var button: Button = findViewById(R.id.button) as
Button
button.hide()

23. Obrigado