Getting Started With Kotlin

Transcript

1. Getting Started With Kotlin On Android Leonardo Pirro Android Developer @ IQUII @lpirro93
2. What is? Statically typed programming language Runs on the JVM Developed by JetBrains, first commit back in 2010 Object-oriented + Functional 100% interoperable with Java
3. Runs on JVM Android Browser Native
4. Android
5. Hello Java My Old Friend • Java is “old” • Inability to add methods to platform types (Util class EVERYWHERE) • Nullability problems (NullPointerException, you know it) • Mutability problems • VERY, VERY, VERY… VER(Y)BOSE. No, serious. Java is Verbose.
7. Hello Java My Old Friend • Java is “old” • Inability to add methods to platform types (Util class EVERYWHERE) • Nullability problems (NullPointerException, you know it) • Mutability problems • VERY, VERY, VERY… VER(Y)BOSE. No, serious. Java is Verbose. • Android API Design • Inheritance • Nullability, again (@Nullable everywhere) • APIs
8. Kotlin to the rescue Kotlin is modern, simple and efficient, developed for Android (and more modern tools) in mind BUT No official support from Google
9. …until Google I/O 2017 Google announces official support for Kotlin, built in Android Studio
10. Kotlin threads analysis on StackOverflow
12. Basic Syntax - Functions fun multiply(op1: Double, op2: Double): Double { return op1*op2; }
13. Basic Syntax - Functions fun multiply(op1: Double, op2: Double): Double { return op1*op2; } fun
14. Basic Syntax - Functions fun multiply(op1: Double, op2: Double): Double { return op1*op2; } op1: Double, op2: Double
15. Basic Syntax - Functions fun multiply(op1: Double, op2: Double): Double { return op1*op2; } : Double
16. Basic Syntax - Functions fun multiply(op1: Double, op2: Double): Double { return op1*op2; }
17. Basic Syntax - Functions fun multiply(op1: Double, op2: Double): Double { return op1*op2 }
18. Basic Syntax - Functions fun multiply(op1: Double, op2: Double) = op1*op2
19. Basic Syntax - Functions fun showToast(message: String, duration: Int){ Toast.makeText(this, message, duration).show() }
20. Basic Syntax - Functions fun showToast(message: String, duration: Int): Unit { Toast.makeText(this, message, duration).show() }
21. Basic Syntax - Functions Default arguments // Java void printMessage(String message) { System.out.println(message); } void printMessage(String message, String prefix){ System.out.format("%s %s", message, prefix); } void printMessage(String message, String prefix,String suffix){ System.out.format("%s %s %s", message, prefix, suffix); } // Kotlin fun printMessage(message: String, prefix: String = "", suffix: String = "") { println("$prefix $prefix $suffix") } printMessage("Uno") printMessage("Uno", "Due", “Tre") printMessage(suffix = "Tre", message = "Uno", prefix = "Due")
22. Variables // Java int a = 1; String b = "i'm the one who knocks"; // Kotlin val a: Int = 1 val b: String = "I'm the one who knocks"
23. Variables // Java int a = 1; String b = "i'm the one who knocks"; // Kotlin val a: Int = 1 val b: String = "I'm the one who knocks"
24. Variables // Java int a = 1; String b = "i'm the one who knocks"; // Kotlin val a = 1 // Inferred type Int val b = "I'm the one who knocks" // Inferred type String
25. (Im)mutability // Immutable Read-only variable val x = 1 x = 2 // Compile-time error "val cannot be reassigned" // Mutable variable var y = 2 y = 2 // OK
26. (Im)mutability // Immutable variable val x = 1 x = 2 // Compile-time error "val cannot be reassigned" // Mutable variable var y = 2 y = 2 // OK // Mutable variable var // Immutable variable val
27. Null Safety: Nullable types and Non-Null types Non-Null types var name: String = "Leonardo" name = null // Compile-time error
28. Null Safety: Nullable types and Non-Null types Non-Null types var name: String? = "Leonardo" name = null // OK
29. Null Safety: Nullable types and Non-Null types fun getLength(string: String?): Int? { if(string != null) { return string.length } return 0 }
31. Null Safety: Nullable types and Non-Null types fun getLength(string: String?): Int? { return string?.length?: 0 }
32. Null Safety: Nullable types and Non-Null types fun getLength(string: String?): Int? { return string!!.length!! } For Null Pointer Exception Fans
33. Null Safety: Nullable types and Non-Null types // Java public ZipCode getZipCode(User user){ if(user != null){ if(user.getAddress() != null){ return user.getAddress().getZipCode(); } } return null; } // Kotlin fun getZipCode(user: User?): ZipCode? { return user?.address?.zipCode }
34. Null Safety: Nullable types and Non-Null types // Java public ZipCode getZipCode(User user){ if(user != null){ if(user.getAddress() != null){ return user.getAddress().getZipCode(); } } return null; } // Kotlin fun getZipCode(user: User?) = user?.address?.zipcode
35. Classes // Java public class MainActivity extends AppCompatActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); } } // Kotlin class MainActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) } }
36. Classes class News (val title: String, val text: String, val tags: List<String>){ init { // Init code can be place here :) } .. }
37. Classes (Models) - Java public class User { String firstName; String lastName; String phone; Date dateOfBirth; String email; public User(String firstName, String lastName, String phone, Date dateOfBirth, String email) { this.firstName = firstName; this.lastName = lastName; this.phone = phone; this.dateOfBirth = dateOfBirth; this.email = email; } public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } public String getPhone() { return phone; } public void setPhone(String phone) { this.phone = phone; } public Date getDateOfBirth() { return dateOfBirth; }
39. Classes - Kotlin (Data classes) data class User(var firstName: String?, var lastName: String?, var phone: String?, var dateOfBirth: Date?) Kotlin Data classes = equals() + hashCode() + toString() + copy() 1 line in Kotlin VS 83+ lines in Java
40. Classes - One Model class to rule them all // Models.kt data class User(val name: String, val surname: String, val email: String) data class Address(val street: String, val zipCode: ZipCode) data class ZipCode(val prefix: String, val postfix: String)
41. Properties class User { var firstName: String? = null // mutable variable (getter/setter) var lastName: String? = null // mutable variable (getter/setter) val age: Int? = null // immutable (getter only) fun test(){ val user = User() // no 'new' keyword user.firstName = "Ajeje" // setter is called user.lastName = "brazof" // setter is called print("The name is ${user.firstName}") // getter is called } }
42. Properties var firstName: String? = "" get() { return "Bla bla bla" }
43. Properties var firstName: String? = "" get() = "bla bla bla" set(value) { field = value + "bla bla bla" }
44. Properties class MainActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) textView.setText("My awesome text") // Java style } }
45. Properties class MainActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) textView.setText("My awesome text") // Java style textView.text = "My awesome text" // Kotlin property access } }
46. Kotlin Synthetic - Goodbye findViewById public class HomeActivity extends AppCompatActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_home); TextView textView = findViewById(R.id.textView); textView.setText("I drink and I know things"); } }
47. Kotlin Synthetic - Goodbye findViewById public class HomeActivity extends AppCompatActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_home); TextView textView = findViewById(R.id.textView); textView.setText("I drink and I know things"); } } TextView textView = findViewById(R.id.textView);
48. Kotlin Synthetic - Goodbye findViewById import kotlinx.android.synthetic.main.content_main.* class MainActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) textView.text = "My awesome text" } }
49. Kotlin Synthetic - Goodbye findViewById import kotlinx.android.synthetic.main.content_main.* class MainActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) textView.text = "My awesome text" } } import kotlinx.android.synthetic.main.content_main.* No findViewById() needed!
50. Extension Functions static boolean isTuesday(Date date){ return date.getDay() == 2; } boolean tuesday = DateUtil.isTuesday(date);
51. Extension Functions fun Date.isTuesday(): Boolean { return getDay() == 2 }
52. Extension Functions fun Date.isTuesday(): Boolean { return getDay() == 2 } Date.
53. Extension Functions fun Date.isTuesday(): Boolean { return getDay() == 2 } val tuesday = date.isTuesday()
54. Extension Functions fun Date.isTuesday() = getDay() == 2 val tuesday = date.isTuesday()
55. Extension Functions Toast.makeText(context, "Message", Toast.LENGTH_SHORT).show();
56. Extension Functions fun Toast.show(message: String, duration: Int){ Toast.makeText(this, message, duration).show() } Toast.show("My message", Toast.LENGTH_LONG )
57. Extension Functions fun Toast.show(message: String, duration: Int = Toast.LENGTH_SHORT){ Toast.makeText(this, message, duration).show() } Toast.show("My message", Toast.LENGTH_LONG )
58. Extension Functions fun Toast.show(message: String, duration: Int = Toast.LENGTH_SHORT){ Toast.makeText(this, message, duration).show() } Toast.show("My message") Toast.makeText(context, "Message", Toast.LENGTH_SHORT).show(); VS
59. High-Order Functions fun <T> List<T>.filter (predicate: (T) -> Boolean): List<T>{ val filteredList = ArrayList<T>() for(item in this){ if(predicate(item)){ filteredList.add(item) } } return filteredList } val names = listOf("Leonardo", "Federico", "Marco", "Daniele") val l = names.filter { it == "Leonardo" }
60. Extension Function Expressions db.beginTransaction(); try { db.delete("news", "news_id = ?", new String[] {"46"}); } finally { { db.endTransaction(); } }
61. Extension Function Expressions db.beginTransaction(); try { db.delete("news", "news_id = ?", new String[] {"46"}); db.setTransactionSuccessful(); } finally { { db.endTransaction(); } }
62. Extension Function Expressions fun SQLiteDatabase.inTransaction(func: () -> Unit){ beginTransaction() try{ func() setTransactionSuccessful() } finally { endTransaction() } } db.inTransaction { db.delete("news", "news_id = ?", arrayOf("46")) }
63. Extension Function Expressions fun SQLiteDatabase.inTransaction(func: () -> Unit){ beginTransaction() try{ func() setTransactionSuccessful() } finally { endTransaction() } } db.inTransaction { db.delete("news", "news_id = ?", arrayOf("46")) }
64. Extension Function Expressions fun SQLiteDatabase.inTransaction(func: (SQLiteDatabase) -> Unit){ beginTransaction() try{ func() setTransactionSuccessful() } finally { endTransaction() } } db.inTransaction { db.delete("news", "news_id = ?", arrayOf("46")) }
65. Extension Function Expressions fun SQLiteDatabase.inTransaction(func: (SQLiteDatabase) -> Unit){ beginTransaction() try{ func(this) setTransactionSuccessful() } finally { endTransaction() } } db.inTransaction { db.delete("news", "news_id = ?", arrayOf("46")) }
66. Extension Function Expressions fun SQLiteDatabase.inTransaction(func: (SQLiteDatabase) -> Unit){ beginTransaction() try{ func(this) setTransactionSuccessful() } finally { endTransaction() } } db.inTransaction { db.delete("news", "news_id = ?", arrayOf("46")) }
67. Extension Function Expressions fun SQLiteDatabase.inTransaction(func: (SQLiteDatabase) -> Unit){ beginTransaction() try{ func(this) setTransactionSuccessful() } finally { endTransaction() } } db.inTransaction { it.delete(“news", "news_id = ?", arrayOf("46")) }
68. Extension Function Expressions fun SQLiteDatabase.inTransaction(func: (SQLiteDatabase) -> Unit){ beginTransaction() try{ func(this) setTransactionSuccessful() } finally { endTransaction() } } db.inTransaction { it.delete(“news", "news_id = ?", arrayOf("46")) }
69. Extension Function Expressions fun SQLiteDatabase.inTransaction(func: SQLiteDatabase.() -> Unit){ beginTransaction() try{ func(this) setTransactionSuccessful() } finally { endTransaction() } } db.inTransaction { it.delete(“news", "news_id = ?", arrayOf("46")) }
70. Extension Function Expressions fun SQLiteDatabase.inTransaction(func: SQLiteDatabase.() -> Unit){ beginTransaction() try{ func(this) setTransactionSuccessful() } finally { endTransaction() } } db.inTransaction { it.delete(“news", "news_id = ?", arrayOf("46")) }
71. Extension Function Expressions fun SQLiteDatabase.inTransaction(func: SQLiteDatabase.() -> Unit){ beginTransaction() try{ func() setTransactionSuccessful() } finally { endTransaction() } } db.inTransaction { it.delete(“news", "news_id = ?", arrayOf("46")) }
72. Extension Function Expressions fun SQLiteDatabase.inTransaction(func: SQLiteDatabase.() -> Unit){ beginTransaction() try{ func() setTransactionSuccessful() } finally { endTransaction() } } db.inTransaction { it.delete(“news", "news_id = ?", arrayOf("46")) }
73. Extension Function Expressions fun SQLiteDatabase.inTransaction(func: SQLiteDatabase.() -> Unit){ beginTransaction() try{ func() setTransactionSuccessful() } finally { endTransaction() } } db.inTransaction { delete(“news", "news_id = ?", arrayOf("46")) }
74. Extension Function Expressions fun SharedPreferences.edit(func: SharedPreferences.Editor.() -> Unit){ val editor = edit() editor.func() editor.apply() } preferences.edit { putString("name", "Paolo") putString("surname", "Blabla") remove("name") }
75. Kotlin • Easy to learn • Modern, fast, efficient • Incredible usefull with Android • 100% Interoperable with Java • Makes your code cleaner and elegant
76. Always code as if the guy who ends up maintaining your code will be a violent psychopath who knows where you live. - John F. Woods
77. Link utili • Kotlin community: https://kotlinlang.org/community • Official Slack: http://slack.kotlinlang.org • Android Developers Italy: https://androiddevsitaly.slack.com Slide: https://goo.gl/AXhmQX https://goo.gl/nYLxY7
78. Thank You Leonardo Pirro Android Developer @ IQUII @lpirro93