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Kotlin for Android Developers Antonio Leiva @lime_cl

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http://plex.tv

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http://antonioleiva.com

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No content

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Kotlin features

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What is Kotlin? • JVM based • Object-oriented functional language • Created by JetBrains (IntelliJ, Android Studio) • Simple,lightweight, interoperable

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Kotlin features Title Text Null safety

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Null safety Artist artist = null;
 artist.print(); JAVA Null Pointer Exception

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Null safety KOTLIN var artist: Artist? = null
 artist.print() var artist: Artist? = null
 artist?.print() won´t compile will do nothing if (artist != null) {
 artist.print()
 } Smart cast var artist: Artist? = null
 artist!!.print() will crash

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Kotlin features Title Text Properties

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Properties private String field = “”;
 
 public String getField() {
 return field;
 }
 
 public void setField(String field) {
 this.field = field;
 } JAVA

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Properties var property: String = "" KOTLIN

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Properties var property: String = ""
 get(){
 return "property is $field"
 }
 set(value: String){
 if (value != "")
 field = value
 }

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Kotlin features Title Text Data Classes

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Data Classes public class Artist {
 private long id;
 private String name;
 private String url;
 private String mbid;
 
 public long getId() {
 return id;
 }
 
 public void setId(long id) {
 this.id = id;
 }
 
 public String getName() {
 return name;
 }
 
 public void setName(String name) {
 this.name = name;
 }
 
 public String getUrl() {
 return url;
 }
 
 public void setUrl(String url) {
 this.url = url;
 }
 
 public String getMbid() {
 return mbid;
 }
 
 public void setMbid(String mbid) {
 this.mbid = mbid;
 }
 
 @Override public String toString() {
 return "Artist{" +
 "id=" + id +
 ", name='" + name + '\'' +
 ", url='" + url + '\'' +
 ", mbid='" + mbid + '\'' +
 '}';
 }
 }
 JAVA

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Data Classes data class Artist(
 var id: Long,
 var name: String,
 var url: String,
 var mbid: String) KOTLIN

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Kotlin is functional

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Kotlin is functional (kind of)

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Kotlin is functional Lambdas

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Lambdas function: (T) -> R

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Lambdas public interface Callback {
 void invoke(T result);
 }
 
 public void asyncOperation(int value, Callback callback){
 ...
 callback.invoke(true);
 } JAVA asyncOperation(5, new Callback() {
 @Override public void invoke(Boolean result) {
 System.out.println("Result: " + result);
 }
 });

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Lambdas fun asyncOperation(value: Int, callback: (Boolean) -> Unit) {
 ...
 callback(true)
 } asyncOperation(5) { result ->
 println("result: $result")
 }

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Lambdas fun asyncOperation(value: Int, callback: (Boolean) -> Unit) {
 ...
 callback(true)
 } asyncOperation(5) { result ->
 println("result: $result")
 } asyncOperation(5) { println("result: $it") }

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Lambdas asyncOperation(5) { println("result: $it") } asyncOperation(5, new Callback() {
 @Override public void invoke(Boolean result) {
 System.out.println("Result: " + result);
 }
 });

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Kotlin is functional Collections

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Collections • Iterable • Collection • List • Set • Map filter sort map zip dropWhile first firstOrNull last lastOrNull fold …

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Collections parsedContacts .filter { it.name != null && it.image != null }
 .sortedBy { it.name }
 .map { Contact(it.id, it.name!!, it.image!!) }

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Kotlin is functional Extending language

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Extending language inline fun supportsLollipop(code:() -> Unit) {
 if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP){
 code.invoke()
 }
 } supportsLollipop {
 getWindow().setStatusBarColor(Color.BLACK)
 }

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More awesome features!

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More awesome features! Extension functions

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Extension functions fun Context.toast(message: CharSequence){
 Toast.makeText(this, message, duration).show()
 }

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Extension functions fun Context.toast(message: CharSequence){
 Toast.makeText(this, message, duration).show()
 } context.toast("I'm a context")
 activity.toast("I'm an activity")
 service.toast("I'm a service")

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Extension functions fun Long.toDateString(dateFormat: Int = DateFormat.MEDIUM): String {
 val df = DateFormat.getDateInstance(dateFormat, Locale.getDefault())
 return df.format(this)
 }

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More awesome features! Default arguments

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Default arguments fun Long.toDateString(dateFormat: Int = DateFormat.MEDIUM): String {
 val df = DateFormat.getDateInstance(dateFormat, Locale.getDefault())
 return df.format(this)
 }

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Default arguments fun Long.toDateString(dateFormat: Int = DateFormat.MEDIUM): String {
 val df = DateFormat.getDateInstance(dateFormat, Locale.getDefault())
 return df.format(this)
 } dateLong.toDateString()
 dateLong.toDateString(DateFormat.FULL)

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Default arguments fun Activity.toast(message: CharSequence, duration: Int = Toast.LENGTH_SHORT){
 Toast.makeText(this, message, duration).show()
 } toast(“Short Toast!!”) toast("Long Toast!!", Toast.LENGTH_LONG)

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More awesome features! Interfaces

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Interfaces • Can contain code (but not state) interface ToolbarManager {
 
 val toolbar: Toolbar
 
 fun initToolbar() {
 toolbar.inflateMenu(R.menu.menu_main)
 toolbar.setOnMenuItemClickListener {
 when (it.itemId) {
 R.id.action_settings -> App.instance.toast("Settings")
 else -> App.instance.toast("Unknown option")
 }
 true
 }
 }
 }

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Interfaces class MainActivity : AppCompatActivity(), ToolbarManager {
 
 override val toolbar by lazy { find(R.id.toolbar) }
 
 override fun onCreate(savedInstanceState: Bundle?) {
 super.onCreate(savedInstanceState)
 setContentView(R.layout.activity_main)
 initToolbar()
 ...
 }
 }


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More awesome features! Property delegation

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Property delegation val toolbar by lazy { find(R.id.toolbar) } • Lazy var p by Delegates.observable("") { d, old, new -> db.saveChanges(this, new) } • Observable • Not Null • Vetoable • Values from map • Custom

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More awesome features! Flow control

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Flow control • If • When • For • While

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Flow control • If val z = if (condition) x else y

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Flow control • When val cost = when(x) {
 in 1..10 -> "cheap"
 in 10..100 -> "regular"
 in 100..1000 -> "expensive"
 in specialValues -> "special value!"
 else -> "not rated"
 }

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Flow control • When val res = when {
 x in 1..10 -> "cheap"
 s.contains("hello") -> "it's a welcome!"
 v is ViewGroup -> "child count: ${v.getChildCount()}"
 else -> ""
 }

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More awesome features! Title Text Interoperability

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Interoperability Palette.generateAsync(bitmap, new Palette.PaletteAsyncListener() {
 @Override public void onGenerated(Palette palette) {
 …
 }
 }); JAVA

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Interoperability Palette.generateAsync(bitmap, new Palette.PaletteAsyncListener() {
 @Override public void onGenerated(Palette palette) {
 …
 }
 }); Palette.generateAsync(bitmap) { palette ->
 …
 } JAVA KOTLIN

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Interoperability view.setOnClickListener(object : View.OnClickListener{
 override fun onClick(v: View) {
 toast("Click")
 }
 }) Regular anonymous class (similar to Java)

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Interoperability If interface only has a function, substitute by function view.setOnClickListener({ view ->
 toast("Click")
 })

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Interoperability view.setOnClickListener({
 toast("Click")
 }) If interface only has a function, substitute by function view.setOnClickListener({ view ->
 toast("Click")
 })

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Interoperability view.setOnClickListener() {
 toast("Click")
 } If last parameter is a function, can go out of parenthesis

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Interoperability view.setOnClickListener() {
 toast("Click")
 } If last parameter is a function, can go out of parenthesis view.setOnClickListener {
 toast("Click")
 }

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Interoperability view.setOnClickListener(object : View.OnClickListener{
 override fun onClick(v: View) {
 toast("Click")
 }
 }) view.setOnClickListener { toast("Click") }

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Interoperability Getter (+Setter) -> Property supportActionBar.title = title
 textView.text = title contactsList.adapter = ContactsAdapter()

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Kotlin Android Extensions

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Kotlin Android Extensions Direct access to XML views using its id as property name main.xml 
 
 
 


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Kotlin Android Extensions Import synthetic properties import kotlinx.android.synthetic.main.* Use the properties override fun onCreate(savedInstanceState: Bundle?) {
 super.onCreate(savedInstanceState) setContentView(R.id.main)
 frameLayout.setVisibility(View.VISIBLE)
 welcomeText.setText("I´m a welcome text!!")
 }

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Anko

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Anko UI declaration DSL

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UI declaration DSL verticalLayout {
 val name = editText()
 button("Say Hello") {
 onClick { toast("Hello, ${name.text}!") }
 }
 }

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Anko Useful extensions

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Useful extensions startActivity("id" to res.id, "name" to res.name) Start an activity Access to system services context.layoutInflater context.notificationManager
 context.sensorManager
 context.vibrator

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Useful extensions Toasts and Alert dialogs toast(R.string.message)
 longToast("Wow, such a duration")
 
 alert("Yes /no Alert") {
 positiveButton("Yes") { submit() }
 negativeButton("No") {}
 }.show()

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Anko Easy asynchrony

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Easy asynchrony async {
 val result = longRequest()
 uiThread { bindForecast(result) }
 }

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Anko SQLite helpers

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SQLite helpers ManagedSQLiteOpenHelper dbHelper.use {
 select("TABLE_NAME").where("_id = {id}", "id" to 20)
 } db.createTable("TABLE_NAME", true,
 "_id" to INTEGER + PRIMARY_KEY,
 "name" to TEXT) parseList / parseOpt / classParser…

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Conclusion

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Conclusion • Lightweight, simple and powerful • Simplifies Android Development • Version 1.0 -> soon!

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http://antonioleiva.com/book/ Kotlin for Android Developers • Create App from scratch • Step by step • Complete Kotlin coverage • Updated to latest version

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http://antonioleiva.com/book/ ?