Criando app Android utilizando Kotlin

CRIANDO APP ANDROID UTILIZANDO KOTLIN
Luiz Santana / André Cardoso

- Java 8 no Android N
- Streams
- API level 23 ou RxJava
- Lambdas, referências à métodos, non-capturing
- API level 23 ou Retrolambda
- Try with resources
- API level 19 ou Retrolambda
- Métodos default em interfaces
- API level 23
Android Moderninho

- Não dá pra adicionar métodos à tipos existentes
- *Util em todo lugar
- Nulls
- NPEs em todo lugar
- Java é verboso
- APIs do Android são complexas
- Herança e nulls em todo lugar
Limitações do Java no Android

- JetBrains
- JVM
- Concisa, Segura, Versátil, Interoperável

package hello 
 
fun main(args: Array<String>) { 
println("Hello TDC!") 
}

fun welcome(name: String, event: String): String { 
return "Hello ${name}, welcome to ${event}!" 
}
Functions

fun welcome(name: String, event: String) =
"Hello ${name}, welcome to ${event}!"
Functions

val greeting = welcome("André", "TDC") 
println(greeting) 
}
Functions

val greeting = welcome("André", "TDC") 
 
greeting = welcome("Luiz", "TDC") 
}
Variáveis

var greeting = welcome("André", "TDC") 
 
greeting = welcome("Luiz", "TDC") 
}
Variáveis

fun welcome(name: String, event: String = "TDC") 
= "Hello ${name}, welcome to ${event}!" 
 
Parâmetros Default

val greeting = welcome("André") 
}
Parâmetros Default

val greeting = welcome(name = "Luiz", event = "I/O") 
}
Parâmetros Default

fun welcome(name: String = "Developer", event: String = "TDC") 
= "Hello ${name}, welcome to ${event}!" 
 
Parâmetros Default

val greeting = welcome(event = “Android Meetup") 
}
Parâmetros Default

val greeting = welcome() 
}
Parâmetros Default

val lyrics = """ 
|Jamais a natureza 
|Reuniu tanta beleza 
|Jamais algum poeta 
|Teve tanto pra cantar! 
“"".trimMargin()
println(lyrics) 
 
val month = "(JAN|FEB|MAR|APR|MAY|JUN|JUL|AUG|SEP|OCT|NOV|DEC)" 
var datePattern = """d{2} ${month} d{4}""" 
 
val today = "13 MAY 2016".matches(Regex(datePattern)) 
println(today)
String Templates

val famousPeople = arrayListOf<String>("Einstein", "Newton", "MC Biel") 
 
val forSure = famousPeople is java.util.ArrayList 
println(forSure)
Collections

val famousPeople = arrayListOf<String>("Einstein", "Newton", "MC Bin Laden") 
 
val pairs = famousPeople.map { Pair(it, it == "MC Bin Laden") } 
 
pairs.forEach { 
val (name, singer) = it 
val verb = if (singer) "is" else "is not" 
println("${name} ${verb} a singer") 
}
Lambdas

val pairs = famousPeople.map { Pair(it, it == "MC Bin Laden") }
Equality

pairs.forEach { 
val (name, singer) = it 
val verb = if (singer) "is" else "is not" 
println("${name} ${verb} a singer") 
}
Destructors e if expressions

fun String.isSinger() = this == "MC Bin Laden"
Extension Functions

val famousPeople = arrayListOf<String>("Einstein", "Newton", "MC Bin Laden") 
 
famousPeople.forEach { 
val verb = if (it.isSinger()) "is" else "is not" 
println("${it} ${verb} a singer") 
}
Extension Functions

fun SQLiteDatabase.transaction(code: SQLiteDatabase.() -> Unit) { 
try { 
beginTransaction() 
code() 
setTransactionSuccessful() 
} catch (e: TransactionAbortException) { 
// Do nothing, just stop the transaction 
} finally { 
endTransaction() 
} 
} 
 
fun SQLiteDatabase.delete(tableName: String, whereClause: String =
"", vararg args: Pair<String, Any>): Int {
… 
}
Extension Functions

db.transaction { 
db.delete("people", "is_singer = ?", "is_singer" to true) 
}
Extension Functions

fun sendEmailToClient(client: Client?, message: String?, mailer: Mailer) { 
val email = client?.personalInfo?.email ?: "someone@isgoingtoreadit.com" 
if (message != null) { 
mailer.sendMessage(email, message) 
} 
}
Tipos Null

} 
}
Null Safe Calls

} 
}
Elvis

} 
}
Smart Cast

fun eval(expr: Expr): Int = 
when (expr) { 
is Num -> expr.value 
is Sum -> eval(expr.left) + eval(expr.right) 
else -> throw IllegalArgumentException("Unknown expression") 
} 
 
interface Expr 
class Num(val value: Int) : Expr 
class Sum(val left: Expr, val right: Expr) : Expr
Smart Cast

class Person constructor(name: String) { 
} 
 
class Singer(name: String, isSinger: Boolean) : Person(name) { 
}
Classes

open class Person constructor(name: String) { 
} 
 
}
Classes

open class Person constructor(name: String) { 
open fun walk() { 
println("walking as a normal person") 
} 
} 
 
override fun walk() { 
println("walking with some style") 
} 
}
Classes

interface Funk { 
var views: Long 
 
fun funk() { 
views++ 
println("ta tranquilo ta favorável") 
} 
}
class Singer(name: String, isSinger: Boolean, override var views:
Long) : Funk
Interfaces

val mc = Singer("MC Bin Laden", true) 
mc.funk() 
mc.walk() 
}
Interfaces

interface Moveable { 
fun move() { print("move") } 
} 
 
interface Walkable { 
fun move() { walk() } 
fun walk() { print("walk") } 
} 
 
class Human : Moveable, Walkable { 
override fun move() { 
super<Walkable>.move() 
} 
}
Interfaces - Resolução de conflitos

data class Singer(val name: String, val isSinger: Boolean, override var
views: Long) : Funk
val mc = Singer("MC Bin Laden", isSinger = true, views = 10000000) 
println(mc.toString()) 
println(mc.hashCode()) 
println(mc.copy(name = "Catra")) 
}
Singer(name=MC Bin Laden, isSinger=true, views=10000001)
-117390027
Singer(name=Catra, isSinger=true, views=10000001)
Data class

class Panelist { 
val presentation : String by lazy { 
"Kotlin!!!!" 
} 
 
var numberOfQuestions : Int by Delegates.observable(0) { 
prop, old, new -> 
println("It was ${old} not it is ${new}") 
} 
}
Delegated properties

CRIANDO O APP | OBJETIVO
- Criar um app em Kotlin
- Consumir dados MOCK, simulando
“News feed” do Reddit

CRIANDO O APP | PRIMEIRO PASSO
- Criar projeto com Activity básica

- Instalando Plugin:
- Preferences
- Plugins
- Buscar por “Kotlin”
CRIANDO O APP | PLUGIN

CRIANDO O APP | CONFIGURANDO
- Abrir painel de ações
- ctrl + shift + A
- cmd + shift + A

apply plugin: 'com.android.application' 
apply plugin: 'kotlin-android' 
 
android { 
… 
sourceSets { 
main.java.srcDirs += 'src/main/kotlin' 
} 
} 
 
dependencies {
… 
compile "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version" 
} 
buildscript { 
ext.kotlin_version = '1.0.1-2' 
repositories { 
mavenCentral() 
} 
dependencies { 
classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version" 
} 
} 
build.gradle

public class MainActivity extends AppCompatActivity { 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
super.onCreate(savedInstanceState); 
setContentView(R.layout.activity_main); 
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
setSupportActionBar(toolbar); 
 
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab); 
fab.setOnClickListener(new OnClickListener(…) {
…
}); 
} 
 
@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
getMenuInflater().inflate(R.menu.menu_main, menu); 
return true; 
}
…
}
MainActivity.java

Java -> Kotlin | CONVERTENDO
- Convertendo código
- Abrir painel ação
- Buscar por “Convert Java…”

class MainActivity : AppCompatActivity() { 
 
override fun onCreate(savedInstanceState: Bundle?) { 
super.onCreate(savedInstanceState) 
setContentView(R.layout.activity_main) 
val toolbar = findViewById(R.id.toolbar) as Toolbar? 
setSupportActionBar(toolbar) 
 
val fab = findViewById(R.id.fab) as FloatingActionButton? 
fab?.setOnClickListener({ view -> Snackbar.make(view, "Replace with your own
action", Snackbar.LENGTH_LONG).setAction("Action", null).show() }) 
} 
 
override fun onCreateOptionsMenu(menu: Menu): Boolean { 
menuInflater.inflate(R.menu.menu_main, menu) 
return true 
}
… 
}
MainActivity.kt

 
override fun onCreate(savedInstanceState: Bundle?)
{ 
super.onCreate(savedInstanceState) 
setContentView(R.layout.activity_main)
… 
MainActivity.kt

… 
val toolbar = findViewById(R.id.toolbar) as Toolbar? 
setSupportActionBar(toolbar) 
 
val fab = findViewById(R.id.fab) as FloatingActionButton? 
fab?.setOnClickListener( 
{ view -> Snackbar.make(view, "Replace with your own
action", Snackbar.LENGTH_LONG).setAction("Action", null).show() }) 
}
… 
}
MainActivity.kt

FRAGMENT | MUDANÇAS
- Adicionado Fragment Management
- Removido Float Button
- Removido Option Menu

FRAGMENT | LAYOUT
- Criando um layout Simples
<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout xmlns:android=“….” 
android:layout_width="match_parent" 
android:layout_height="match_parent"> 
 
<android.support.v7.widget.RecyclerView 
android:id="@+id/news_list" 
android:layout_width="wrap_content" 
android:layout_height="wrap_content"> 
</android.support.v7.widget.RecyclerView>
 
</RelativeLayout>

FRAGMENT | KOTLIN CODE
class NewsFragment : Fragment() { 
private var newsList: RecyclerView? = null 
 
override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?,  
savedInstanceState: Bundle?): View? { 
val view = inflater?.inflate(R.layout.fragment_news, container, false) 
newsList = view?.findViewById(R.id.news_list) as RecyclerView? 
newsList?.setHasFixedSize(true) 
newsList?.layoutManager = LinearLayoutManager(context) 
 
return view 
} 
}

FRAGMENT | KOTLIN CODE
private var newsList: RecyclerView? = null 
 
override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?,  
savedInstanceState: Bundle?): View? { 
val view = inflater?.inflate(R.layout.fragment_news, container, false) 
 
return view 
} 
}
Como melhorar 
o código?

EXTENSION FUNCTIONS | INFLATE
Como fazer o código abaixo ficar mais intuitivo?
… 
val view = inflater?.inflate(R.layout.fragment_news, container, false)  
…
… 
val view = container?.inflate(R.layout.fragment_news)  
…

Como implementar?
// ExtensionsKt.kt 
 
fun ViewGroup.inflate(layoutId : Int) : View { 
return LayoutInflater.from(context).inflate(layoutId, this, false) 
}

Reuso do código
// Java 
ExtensionsKt.inflate(container, R.layout.news_fragment); 
// Kotlin 
container?.inflate(R.layout.fragment_news)
@file:JvmName("ExtensionsUtils") 
package com.arctouch.kotlin.commons.extensions 
… 
// Usar assim em Java:
ExtensionsUtils.inflate(container, R.layout.news_fragment);

Parâmetros com valor padrão
fun ViewGroup.inflate(layoutId : Int, attachToRoot : Boolean = false) : View { 
return LayoutInflater.from(context).inflate(layoutId, this, attachToRoot) 
} 
 
// usar assim
val view = container?.inflate(R.layout.fragment_news) // default: false
 
// ou assim 
val view = container?.inflate(R.layout.fragment_news, true)

ANDROID EXTENSIONS | ADICIONANDO
apply plugin: 'com.android.application' 
apply plugin: 'kotlin-android' 
apply plugin: 'kotlin-android-extensions'
Adicionar no build.gradle

ANDROID EXTENSIONS | FUNCIONALIDADE
- Voltando ao Layout do Fragment…
<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout xmlns:android=“….” 
android:layout_width="match_parent" 
android:layout_height="match_parent"> 
 
<android.support.v7.widget.RecyclerView 
android:id="@+id/news_list" 
android:layout_width="wrap_content" 
android:layout_height="wrap_content"> 
</android.support.v7.widget.RecyclerView>
 
</RelativeLayout>

ANDROID EXTENSIONS | FUNCIONALIDADE
// importar no código
// import kotlinx.android.synthetic.<MODULO>.<VIEW>.*
import kotlinx.android.synthetic.main.fragment_news.*
// código antigo 
 
// código novo 
news_list.setHasFixedSize(true) 
news_list.layoutManager = LinearLayoutManager(context)

LAZY PROPERTIES | INTRO
private val newsList by lazy { 
news_list 
}
override fun onActivityCreated(savedInstanceState: Bundle?) { 
super.onActivityCreated(savedInstanceState) 
 
newsList.setHasFixedSize(true) // Executado de maneira Lazy 
newsList.layoutManager = LinearLayoutManager(context) 
} 
}

CRIANDO ADAPTER | INICIO
- Usaremos padrão DelegateAdapter
- A ideia é ter diferentes tipos de view
num mesmo adapter
- Neste caso teremos algo parecido com:

CRIANDO ADAPTER | ESTRUTURA
- Cada ViewItem possui um ViewType
enum class ViewType { 
LOADING, 
NEWS 
}
interface ViewDelegate { 
fun getType() : ViewType 
}

CRIANDO ADAPTER | O ADAPTER
- Nosso NewsAdapter
 
class NewsAdapter : RecyclerView.Adapter<RecyclerView.ViewHolder>() { 
 
private val items: ArrayList<ViewItem> = ArrayList()
// outros métodos… 
}

- Nosso NewsAdapter
 
 
private val items: ArrayList<ViewItem> = ArrayList() 
private val delegateAdapters: HashMap<ViewType, 
ViewTypeDelegateAdapter> = HashMap() 
}

- Nosso NewsAdapter
 
 
private val delegateAdapters: HashMap<ViewType, ViewTypeDelegateAdapter>
= HashMap() 
 
init { 
delegateAdapters.put(ViewType.LOADING, LoadingDelegateAdapter()) 
}
}

- Nosso NewsAdapter
 
 
private val delegateAdapters: HashMap<ViewType, ViewTypeDelegateAdapter> = HashMap() 
private val loadingItem = object : ViewItem { 
override fun getType() : ViewType = ViewType.LOADING 
} 
 
init { 
delegateAdapters.put(ViewType.LOADING, LoadingDelegateAdapter()) 
items.add(loadingItem) 
}
}

DATA CLASSES | MODEL
- Clássico Java model
public class RedditNewsItem { 
private String author; 
private String title; 
 
public RedditNewsItem(String author, String title) { 
this.author = author; 
this.title = title; 
} 
 
public String getAuthor() { 
return author; 
} 
 
public void setAuthor(String author) { 
this.author = author; 
} 
 
public String getTitle() { 
return title; 
} 
 
public void setTitle(String title) { 
this.title = title; 
} 
}

DATA CLASSES | MODEL
- Kotlin data class
data class RedditNewsItem(var author: String, var title: String)
 
Java Model +  
equals/hashCode  
toString 
copy

DELEGATE ADAPTERS | ESTRUTURA
- Criando estrutura inicial
interface ViewTypeDelegateAdapter { 
fun onCreateViewHolder(parent: ViewGroup): RecyclerView.ViewHolder 
fun onBindViewHolder(holder: RecyclerView.ViewHolder, item: ViewType) 
}

DELEGATE ADAPTERS | LOADING
LoadingDelegateAdapter.kt
class LoadingDelegateAdapter : ViewTypeDelegateAdapter { 
 
override fun onCreateViewHolder(parent: ViewGroup): RecyclerView.ViewHolder 
= SpinnerViewHolder(parent) 
 
override fun onBindViewHolder(holder: RecyclerView.ViewHolder, item: ViewType) { } 
 
class SpinnerViewHolder(parent : ViewGroup) : RecyclerView.ViewHolder 
(parent.inflate(R.layout.news_item_loading)) { 
// infla layout em cima do pai 
} 
}

DELEGATE ADAPTERS | LOADING
LoadingDelegateAdapter.kt
class LoadingDelegateAdapter : ViewTypeDelegateAdapter { 
 
override fun onCreateViewHolder(parent: ViewGroup): RecyclerView.ViewHolder 
= SpinnerViewHolder(parent) 
 
override fun onBindViewHolder(holder: RecyclerView.ViewHolder, item: ViewType) { } 
 
class SpinnerViewHolder(parent : ViewGroup) : RecyclerView.ViewHolder 
// infla layout dentro do container pai 
} 
}

DELEGATE ADAPTERS | NEWS
NewsDelegateAdapter.kt
class NewsAdapterDelegate : ViewTypeDelegateAdapter { 
override fun onCreateViewHolder(parent: ViewGroup): RecyclerView.ViewHolder = NewsViewHolder(parent) 
 
override fun onBindViewHolder(holder: RecyclerView.ViewHolder, item: ViewItem) { 
holder as NewsViewHolder 
holder.bind(item as RedditNewsItem) 
} 
 
class NewsViewHolder(parent : ViewGroup) : RecyclerView.ViewHolder 
 
fun bind(item : RedditNewsItem) = with(itemView) { 
img_thumbnail.loadImgUrl(item.thumbnail) 
description.text = item.title 
author.text = item.author 
comments.text = "${item.commentsNumber} comments" 
} 
} 
}

NewsDelegateAdapter.kt
class NewsAdapterDelegate : ViewTypeDelegateAdapter { 
override fun onCreateViewHolder(parent: ViewGroup): RecyclerView.ViewHolder = NewsViewHolder(parent) 
 
override fun onBindViewHolder(holder: RecyclerView.ViewHolder, item: ViewItem) { 
holder as NewsViewHolder 
holder.bind(item as RedditNewsItem) 
} 
 
class NewsViewHolder(parent : ViewGroup) : RecyclerView.ViewHolder 
 
fun bind(item : RedditNewsItem) = with(itemView) { 
img_thumbnail.loadImgUrl(item.thumbnail) 
description.text = item.title 
author.text = item.author 
comments.text = "${item.commentsNumber} comments" 
} 
} 
}
Smart cast

- Carregando imagem no bind
- Extension functions
 
fun ImageView.loadImgUrl(imageUrl: String?) { 
if (imageUrl.isNullOrEmpty()) { 
Picasso.with(context).load(R.mipmap.ic_launcher).into(this) 
} else { 
Picasso.with(context).load(imageUrl).into(this) 
} 
}

ADICIONANDO ALGUNS DADOS MOCK
// … 
// … 
val newsAdapter = NewsAdapter() 
newsList.adapter = newsAdapter 
 
if (savedInstanceState == null) { 
newsAdapter.addNews(mockData()) 
} 
} 
 
private fun mockData() : List<RedditNewsItem> { 
val news = mutableListOf<RedditNewsItem>() 
 
for (i in 1..10) { 
news.add(RedditNewsItem( 
"Author $i", 
"Title $i", 
"http://lorempixel.com/200/200/technics/$i", // thumbnail 
i // number of comments 
)) 
} 
 
return news 
} 
}

// … 
// … 
val newsAdapter = NewsAdapter() 
newsList.adapter = newsAdapter 
 
if (savedInstanceState == null) { 
newsAdapter.addNews(mockData()) 
} 
} 
}

// … 
private fun mockData() : List<RedditNewsItem> { 
val news = mutableListOf<RedditNewsItem>() 
 
for (i in 1..10) { 
news.add(RedditNewsItem( 
"Author $i", 
"Title $i", 
"http://lorempixel.com/200/200/technics/$i", // thumbnail 
i // number of comments 
)) 
} 
return news 
} 
}

OUTRAS DICAS | CLICK LISTENERS
myButton.setOnClickListener { navigateToDetail() }

OUTRAS DICAS | OPTION MENU
override fun onOptionsItemSelected(item: MenuItem) = when (item.itemId) {
R.id.action_settings -> consume { navigateToSettings() }
R.id.nav_camera -> drawer.consume { navigateToCamera() }
R.id.nav_gallery -> drawer.consume { loadGallery() }
R.id.nav_slideshow -> drawer.consume { loadSlideshow() }
else -> super.onOptionsItemSelected(item)
}

OUTRAS DICAS | OPTION MENU
inline fun consume(f: () -> Unit): Boolean {
f()
return true
}
inline fun DrawerLayout.consume(f: () -> Unit): Boolean {
f()
closeDrawers()
return true
}

OUTRAS DICAS | LAMBDAS
view.postDelayed({ doWhatever() }, 200) 
 
 
Thread().run {
// Running in a thread
}

OUTRAS DICAS | COLLECTIONS
return parsedContacts.filter { it.name != null && it.image != null }
.sortedBy { it.name }
.map { Contact(it.id, it.name!!, it.image!!) }

OUTRAS DICAS | ANKO
- DSL
- Useful Helpers

OUTRAS DICAS | ANKO - DSL
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
verticalLayout {
padding = dip(30)
editText {
hint = "Name"
textSize = 24f
}
editText {
hint = "Password"
textSize = 24f
}
button("Login") {
textSize = 26f // usando tamanho em SP
}
}
}

OUTRAS DICAS | ANKO - Useful Helpers
- Fazer ligação makeCall(numeroTelefone)
- Abrir browser browse(url) 
- Compartilha texto share(text, [assunto]) 
- Enviar email email(email, [assunto], [texto]) 
- Abrir activity startActivity<SomeOtherActivity>("id" to 5)

OUTRAS DICAS | ANKO - Useful Helpers
async() {
// Faz algo em background
uiThread {
// Volta para main thread
}
}

LINKS
Kotlin Lang:
- https://kotlinlang.org/
Kotlin Roadmap
- http://go.arctouch.com/kotlin-roadmap

https://github.com/arctouch-luizsantana/tdc-kotlin

OBRIGADO.
Big Brains Wanted
Join our team! Go to arctouch.com/brjobs
Visit our booth to win an Apple Watch.

Criando app Android utilizando Kotlin

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