Kotlin for Android Developers

Talk about Kotlin for android developers, a introduction to Kotlin Language and some tips apply to Android develop

1. for Android Developers @camachoyury
3. Java • Missing modern features • NPE • JDK 6-7 • No lambdas • No streams • Too Much ceremony
4. History • 2011, released as official project by Jetbrains • 2012, Jetbrains Open Sourced the project, license Apache 2 • 2015, released first Kotlin beta version 1.0 • 2016, Kotlin 1.0 released • 2016 Gradle announces official support • 2017, released 1.1 • and…….
5. History
6. What is Kotlin?
7. What is Kotlin?
8. Where can this run? JVM Android Browser Native
9. Which tools I could use?
10. What is Kotlin? • JVM • Seems Java • Object Oriented • Functional • Do more with less • Complete interop with Java • Null safety
11. Source: https://goo.gl/KkMPYg What is Kotlin?
12. No classes are needed fun main(args: Array<String>){ println("Hello GDG Lima!! You Rocks") }
13. Variables val name: String = "Kylo Ren" var side = "Force" side = "Dark Side" name = "Kylo" //no compile!!! and mutability
14. Functions fun tellMeYourName(person: Person) :String { return person.name }
15. Null Safety var name: String = null name = "Juan" name?.trim() // does runs name!!.trim() // runs anyway ? val lastName: String = "Perez" lastName.trim() // no need for "?."
16. No Lambdas in Java public List<Integer> evens(List<Integer> nums){ List<Integer> numsCopy = new ArrayList<>(nums); Iterator<Integer> numsItr = numsCopy . listIterator (); while (numsItr.hasNext()) { Integer num = numsItr . next (); if (num % 2 != 0) numsItr.remove(); } return numsCopy; }
17. Lambdas fun evens(nums: List<Int>) = nums.filter { it % 2 == 0 }
18. POJO JAVA public static class Person { private String mName; public Person(String name) { mName = name; } public String getName() { return mName; } public void setName(String name) { mName = name; } @Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; Person person = (Person) o; return mName != null ? mName.equals(person.mName) : person.mName == null; } @Override public int hashCode() { return mName != null ? mName.hashCode() : 0; } }
19. Bye Bye POJO data class Person(var name: String)
20. Optional Arguments class Character(name: String, gun: Boolean = false ){ val name = name; var gun = gun } var bruceLee = Character("Bruce Lee") var rambo = Character("Rambo", true)
21. Named Arguments class Character(name: String, gun: Boolean = false ){ val name = name; var gun = gun } var rambo = Character(gun = true, name = "Rambo")
22. Extension Functions fun String.printYourSelf(){ println(this) } "Force be with you!!!".printYourSelf()
23. Extension Functions infix fun Character.fight(character: Character){ println("fighting ${this.name} and ${character.name} ") } rambo fight bruceLee
24. Inheritance open class Person(var name: String){ } class Character(name: String) : Person(name){ }
25. Operator Overload operator fun Character.plus(character: Character){ println( "${this.name} y ${character.name} ") } jhonSmith + janeSmith > Jhon Smith y Jane Smith
26. Kotlin For Android Developers
27. Extension functions in android //JAVA Toast.makeText(getBaseContext(),"#IOLima2017", Toast.LENGTH_SHORT).show(); //Kotlin fun Activity.toast(message: CharSequence, duration: Int = Toast.LENGTH_LONG){ Toast.makeText(this, message, duration).show() } toast("#IOLima2017")
28. Extension functions in android //JAVA public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { // Inflate the layout for this fragment return inflater.inflate(R.layout.main, container, false); } //KOTLIN fun ViewGroup.inflate(layoutId: Int, attachRoot:Boolean = false): View { return LayoutInflater.from(context).inflate(layoutId, this, attachRoot) } return container.inflate(R.layout.main)
29. Android extensions • Better than Butter Knife • No need for instance variables
30. how use it ? Add this line in Build.gradle apply plugin: 'kotlin-android-extensions' Import synthetic layout import kotlinx.android.synthetic.<layout>.*
31. Example with Java <TextView android:id="@+id/hello" android:layout_width="fill_parent" android:layout_height="wrap_content"/> public class MyActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.main) TextView text = (TextView) findViewById(R.id.hello); } }
32. Example Android Extensions <TextView android:id="@+id/hello" android:layout_width="fill_parent" android:layout_height="wrap_content"/> import kotlinx.android.synthetic.main.* public class MyActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.main) this.hello.setText("Hi!") } }
33. Example: Login Facebook - Java //Java loginButton = (LoginButton)findViewById(R.id.login_button); loginButton.registerCallback(callbackManage......
34. Example : Login Facebook - Kotlin //Kotlin loginButton!!.registerCallback(callbackManager, facebookCallback)
35. Anko • Programmatic layouts • DSL instead of XML • Compact and readable • Ide Integration with previews
36. Anko Source: blog.jetbrains.com
37. Adopters
38. Example code: Kotlin and Vision API https://github.com/camachoyury/FaceTracker
39. Questions?, sure please!
40. Main Reference https://kotlinlang.org https://antonioleiva.com/ Books:
41. Other references http://kotlin.es/ http://devcode.la/cursos/kotlin https://codigofacilito.com/cursos/kotli https://www.udemy.com/curso-kotlin/ https://devexperto.com/
42. Gracias! @camachoyury