Kotlin for Android Developers - DevFest Chicago / DC

1. Kotlin for Android Developers Michael Evans @m_evans10 +MichaelEvans michaelevans.org
2. Kotlin for Android Developers Michael Evans LivingSocial @m_evans10
3. Kotlin for Android Developers Michael Evans LivingSocial @m_evans10
4. Kaitlin for Android Developers Michael Evans LivingSocial @m_evans10
5. Kotlin? • Statically Typed • Developed by JetBrains • 100% interoperable with Java
6. Why Kotlin? • Mutability problems • General verbosity • No control over platform types
7. Nullability
8. Nullability I call it my billion-dollar mistake. It was the invention of the null reference in 1965 […] This has led to innumerable errors, vulnerabilities, and system crashes, which have probably caused a billion dollars of pain and damage in the last forty years.
9. Why Kotlin? • Type inference • Lambdas • Null safety • Smart casts • String templates • Higher order functions • Extension functions • Data classes • Default Values
10. Getting Started
11. Getting Started buildscript {
 repositories {
 mavenCentral()
 }
 dependencies {
 classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:1.0.3"
 }
 }
 
 apply plugin: 'kotlin'
 
 dependencies {
 compile "org.jetbrains.kotlin:kotlin-stdlib:1.0.3" }

12. Getting Started buildscript {
 repositories {
 mavenCentral()
 }
 dependencies {
 classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:1.0.3"
 }
 }
 
 apply plugin: 'kotlin'
 
 dependencies {
 compile "org.jetbrains.kotlin:kotlin-stdlib:1.0.3" }

13. Syntax
14. fun sum(a: Int, b: Int): Int {
 return a + b
 } Syntax
15. fun sum(a: Int, b: Int): Int {
 return a + b
 } Syntax
16. Syntax fun sum(a: Int, b: Int): Int {
 return a + b
 }
17. fun sum(a: Int, b: Int): Int {
 return a + b
 } Syntax
18. fun sum(a: Int, b: Int) = a + b
 Syntax
19. Defining Variables final int a = 1;
 
 
 int x = 5;
20. Defining Variables val a: Int = 1
 val b = 1
 
 var x = 5
 x += 1 final int a = 1;
 
 
 int x = 5;
21. Defining Variables val a: Int = 1
 val b = 1
 
 var x = 5
 x += 1 final int a = 1;
 
 
 int x = 5;
22. Properties public class Person {
 
 private String name;
 
 public String getName() {
 return name;
 }
 
 public void setName(String name) {
 this.name = name;
 }
 }
23. Properties var person = Person()
 person.name = "Mike"
 val name = person.name class Person {
 
 var name: String = "Ryan"
 }
24. String Templates var person = Person("Mike")
 
 println("Hello my name is ${person.name}")
25. Nullability Make NullPointerException happen at compile time, not runtime.
26. val string: String = "Mike"
 val another: String = null // does not compile
 
 val nullable: String? = null // ok Nullability
27. Nullability if (files != null) {
 return files.size
 }
28. Nullability println(person?.name)
 
 val email = data["email"] ?: "foo@bar.com"
 
 data?.let {
 // execute this block if not null
 
 println(files!!.size)
29. Nullability println(person?.name?.length)
 
 val email = data["email"] ?: "foo@bar.com"
 
 data?.let {
 // execute this block if not null
 
 println(files!!.size)
30. Nullability println(person?.name?.length)
 
 val email = data["email"] ?: "foo@bar.com"
 
 data?.let {
 // execute this block if not null
 
 println(files!!.size)
31. Nullability println(person?.name?.length)
 
 val email = data["email"] ?: "foo@bar.com" 
 println(files!!.size)
32. fun toast(message: String, length: Int = Toast.LENGTH_SHORT) {
 Toast.makeText(this, message, length).show()
 } Default Values
33. fun toast(message: String, length: Int = Toast.LENGTH_SHORT) {
 Toast.makeText(this, message, length).show()
 } toast("Hello")
 toast("Hello", Toast.LENGTH_LONG)
 toast("Hello", length = Toast.LENGTH_LONG) Default Values
34. Extension Functions fun List.swap(index1: Int, index2: Int) {
 val tmp = this[index1]
 this[index1] = this[index2]
 this[index2] = tmp
 }
35. fun Activity.toast(message: CharSequence, duration: Int = Toast.LENGTH_SHORT) {
 Toast.makeText(this, message, duration).show()
 } fun List.swap(index1: Int, index2: Int) {
 val tmp = this[index1]
 this[index1] = this[index2]
 this[index2] = tmp
 } Extension Functions
36. { it.isEmpty() } 
 { it.length == 10 } 
 { isPalindrome(it) } Function Expressions
37. { it.isEmpty() } 
 { it.length == 10 } 
 { isPalindrome(it) } Function Expressions
38. { it.isEmpty() } 
 { it.length == 10 } 
 { isPalindrome(it) } Function Expressions
39. val isEmpty: (String) -> Boolean = { it.isEmpty() } 
 val exactly10: (String) -> Boolean = { it.length == 10 } 
 val palindrome: (String) -> Boolean = { isPalindrome(it) } Function Expressions
40. fun <T> List<T>.filter(predicate: (T) -> Boolean): List<T> {
 // ...
 } Higher order functions
41. Higher order functions fun <T> List<T>.filter(predicate: (T) -> Boolean): List<T> {
 val newList = ArrayList<T>()
 for (item in this) {
 if(predicate(item)) {
 newList.add(item)
 }
 }
 return newList
 }
42. fun <T> List<T>.filter(predicate: (T) -> Boolean): List<T> {
 // ...
 } Higher order functions val names = listOf("Mike", "John", "Bob")
 names.filter { it == "Mike" } // ["Mike"]
 names.filter(palindrome) // ["Bob"]
43. Examples
44. Extension Functions Picasso.with(imageView.getContext())
 .load(imageUrl)
 .into(imageView);
45. Extension Functions fun ImageView.load(url: String) {
 Picasso.with(context).load(url).into(this)
 }
46. Extension Functions fun ImageView.load(url: String) {
 Picasso.with(context).load(url).into(this)
 } imageView.load("http://...")
47. inline fun supportsLollipop(code: () -> Unit) {
 if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
 code.invoke()
 }
 } Inline Functions
48. supportsLollipop {
 getWindow().setStatusBarColor(Color.BLACK)
 } inline fun supportsLollipop(code: () -> Unit) {
 if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
 code.invoke()
 }
 } Inline Functions
49. public class ContactsAdapter extends RecyclerView.Adapter {
 interface ContactClickListener {
 void onContactClicked(Contact contact);
 }
50. public class ContactsAdapter extends RecyclerView.Adapter {
 interface ContactClickListener {
 void onContactClicked(Contact contact);
 } recycler.setAdapter(new ContactsAdapter(contacts, new ContactsAdapter.ContactClickListener() {
 @Override
 public void onContactClicked(ContactsAdapter.Contact contact) {
 
 }
 }));
51. recycler.adapter = ContactsAdapter(contacts) {
 navigateToDetail(it)
 }
 
 class ContactsAdapter(val contacts: List<Contact>,
 val listener: (Contact) -> Unit)
 
 itemView.setOnClickListener { listener(contact) }
52. recycler.adapter = ContactsAdapter(contacts) {
 navigateToDetail(it)
 }
 
 class ContactsAdapter(val contacts: List<Contact>,
 val listener: (Contact) -> Unit)
 
 itemView.setOnClickListener { listener(contact) }
53. recycler.adapter = ContactsAdapter(contacts) {
 navigateToDetail(it)
 }
 
 class ContactsAdapter(val contacts: List<Contact>,
 val listener: (Contact) -> Unit)
 
 itemView.setOnClickListener { listener(contact) }
54. Extension Function Expressions
55. Extension Function Expressions SharedPreferences.Editor editor = getSharedPreferences("prefs", 0).edit();
 editor.putString("this", "that");
 editor.apply();
56. inline fun SharedPreferences.edit( func: SharedPreferences.Editor.() -> Unit) {
 val editor = edit()
 editor.func()
 editor.apply()
 }
 
 Extension Function Expressions
57. inline fun SharedPreferences.edit( func: SharedPreferences.Editor.() -> Unit) {
 val editor = edit()
 editor.func()
 editor.apply()
 }
 
 preferences.edit {
 putString("foo", "bar")
 putString("fizz", "buzz")
 remove("username")
 } Extension Function Expressions
58. inline fun SharedPreferences.edit( func: SharedPreferences.Editor.() -> Unit) {
 val editor = edit()
 editor.func()
 editor.apply()
 }
 
 fun SharedPreferences.Editor.set(pair: Pair<String, String>) =
 putString(pair.first, pair.second) Extension Function Expressions
59. preferences.edit {
 set("foo" to "bar")
 set("fizz" to "buzz")
 remove("username")
 } Extension Function Expressions
60. Libraries
61. verticalLayout {
 padding = dip(30)
 editText {
 hint = "Name"
 textSize = 24f
 }
 editText {
 hint = "Password"
 textSize = 24f
 }
 button("Login") {
 textSize = 26f
 }
 } Anko
62. apply plugin: 'kotlin-android-extensions' import kotlinx.android.synthetic.main.activity_main.* … textView.setText("Hello, world!") Kotlin Extensions for Android
63. Getting started?
64. Java Interoperability
65. Java Interoperability class Person {
 private String name;
 
 public void setName(String name) {
 this.name = name;
 }
 }
66. var person = Person()
 person.name = "name" Java Interoperability class Person {
 private String name;
 
 public void setName(String name) {
 this.name = name;
 }
 }
67. Java Interoperability - Extensions
68. // com/example/util/DateExtensions.kt
 fun Date.isTuesday() = day == 2
 
 // com/example/util/DateExtensionsKt.java
 static boolean isTuesday(Date date) {
 return date.getDay() == 2;
 } Java Interoperability - Extensions
69. // com/example/util/DateExtensions.kt
 fun Date.isTuesday() = day == 2
 
 // com/example/util/DateExtensionsKt.java
 static boolean isTuesday(Date date) {
 return date.getDay() == 2;
 } Java Interoperability - Extensions
70. // com/example/util/DateExtensions.kt @file:JvmName("DateUtils") fun Date.isTuesday() = day == 2
 
 // com/example/util/DateUtils.java
 static boolean isTuesday(Date date) {
 return date.getDay() == 2;
 } Java Interoperability - Extensions
71. Implement Tests in Kotlin
72. Data Classes class Person {
 private String name;
 private int age;
 
 public String getName() {
 return name;
 }
 
 public int getAge() {
 return age;
 }
 }
73. Data Classes @Override public boolean equals(Object o) {
 if (this == o) return true;
 if (o == null || getClass() != o.getClass()) return false;
 
 Person person = (Person) o;
 
 if (age != person.age) return false;
 return name != null ? name.equals(person.name) : person.name == null;
 }
 
 @Override public int hashCode() {
 int result = name != null ? name.hashCode() : 0;
 result = 31 * result + age;
 return result;
 }
 
 @Override public String toString() {
 return super.toString();
 }
 }
74. Data Classes data class Person(val name: String, val age: Int)
75. Convert Java File to Kotlin Kotlin Scripts for Gradle
76. More Info • https://kotlinlang.org • Koans • https://kotlinlang.org/docs/tutorials/koans.html • https://leanpub.com/kotlin-for-android-developers
77. Questions? Michael Evans @m_evans10 +MichaelEvans michaelevans.org
78. Questions? Michael Evans @m_evans10 +MichaelEvans michaelevans.org STICKERS!