Android & Kotlin: The code awakens (episode 03) - 3/3

Kotlin vs Java - Part 3
Extensions
Infix Notation
Operator Overloading

Transcript

1. Android & Kotlin The code awakens #03
2. Omar Miatello Member of GDG Milano (Italy) Android Developer @ Satispay Personal profile google.com/+OmarMiatello Google+ Community: Kotlin for Android goo.gl/mUKF1w Google Presentation #01 goo.gl/0jHLmE #02 goo.gl/h3uG8M #03 goo.gl/hnwvqu Google Photo #01 goo.gl/photos/cKP9L6zqZcxDRGzQ8 #02 goo.gl/photos/sXdpkbihCi5xAAnx7 #03 goo.gl/photos/P6kGhLE8yrWYnhAW6
3. Kotlin 1.0 is out - Read more: goo.gl/5DBQM2
4. dummy/HeroAdapter.java public class HeroAdapter extends RecyclerView.Adapter<HeroAdapter.ViewHolder> { private final List<HeroItem> mValues; private final HeroOnClickListener mListener; public HeroAdapter(List<HeroItem> items, HeroOnClickListener listener) { mValues = items; mListener = listener; } @Override public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_hero, parent, false); return new ViewHolder(view); } @Override public void onBindViewHolder(final ViewHolder holder, int position) { HeroItem item = mValues.get(position); “Convert Java File to Kotlin File” CTRL + ALT + SHIFT + K (or CMD + ALT + SHIFT + K)
5. Previously on Android & Kotlin #01: goo.gl/0jHLmE • Properties val a: Int = 1 // val = READ ONLY (getter) var b: Int = 1 // var = READ/WRITE (getter/setter) • String templates "My name is $name $surname" • Lambdas view.setOnClickListener { Log.d("TAG", "Item clicked!") } • Delegated properties (example: lazy) val item by lazy { MyItem() }
6. // val = READ ONLY (getter) // var = READ/WRITE (getter/setter) val onlyRead = 1 var writable = 2 var nullable: Int? = 3 fun test() { onlyRead = 3 // Error at compile time writable = 3 writable = "test" // Error at compile time writable = null // Error at compile time nullable = null } // Customize getter/setter val p1: Int = 1 get() { // add some logic return field } var p2: Int = 2 get() { return field } set(value) { // add some logic field = value } Properties // More examples
7. var name = "Omar" fun test() { var str: String str = "My name is $name" str = "My name is $name (${name.length} chars)" str = "$name == ${name}" str = "$name.length != ${name.length}" // IS NOT THE SAME str = "Time is: ${System.currentTimeMillis()}ms since 1970" } String templates // More examples
8. "qwerty | 123 | abc".filter { char -> char.isDigit() // return is implicit in lambda expressions } "qwerty | 123 | abc".filter { it.isDigit() // we can use "it" with 1 parameter } "qwerty | 123 | abc".filterIndexed { index: Int, c: Char -> index > 3 && c.isLetterOrDigit() } Lambdas // More examples
9. val startTime by lazy { System.currentTimeMillis() } var test by Delegates.observable(3) { prop, old, new -> if (new > old) Log.w("TEST", "$new > $old") } fun test() { startTime test = 5 test = 1 test = 2 val finish = System.currentTimeMillis() - startTime } Delegated properties // More examples
10. Previously on Android & Kotlin #02: goo.gl/h3uG8M • Null safety var a: String = null // Error at compile time var b: String? = null • Elvis Operator val example: String = b ?: "Default" // b may be null • Smart-cast if (myView is TextView) { myView.setText("Ciao") } • Collections listOf("Android", "iOS", null).filterNotNull().map { it.toUpperCase() }
11. var test: String? = null fun test() { test = "new string" test.length // Error at compile time test?.length // if (test != null) test.length else null test!!.length // test MUST exist or throw NullPointerException val len = test?.length ?: 0 // default value = 0 test?.length ?: throw IllegalStateException("Missing the main string!") } Null safety & Elvis Operator // More examples
12. var test: Any? = "My new value" fun test() { val _test: Any? = test if (_test != null) { val checkEqual = _test.equals("My new value") if (_test is String) { val checkLen = _test.length _test.capitalize() _test.substring(1) } } when (_test) { is Int -> { val sum = _test + 1 } is String -> { val len = _test.length } } } Smart-cast // More examples
13. val stringList = listOf("my", "items", "list") fun test() { stringList.first() stringList.filterNotNull() stringList.filter { it.length > 3 } stringList.first { it.length > 4 } stringList.firstOrNull() { it.length > 10 } stringList.findLast { it.startsWith("m") } stringList.sorted() stringList.indexOfLast { it.startsWith("i") } stringList.map { it.length } stringList.maxBy { it.length } // ... } Collections // More examples
14. Kotlin vs Java - Part 3 Extensions Infix Notation Operator Overloading
15. fun String.isBig(): Boolean { return length() > 10 } #9 Kotlin - Extensions http://kotlinlang.org/docs/reference/extensions.html vs
16. fun String.isBig(): Boolean { return length() > 10 } fun example() { "why?!".isBig() // false! "harder, better, ...".isBig() // true! } #9 Kotlin - Extensions http://kotlinlang.org/docs/reference/extensions.html vs
17. fun String.isBig(): Boolean { return length() > 10 } fun example() { "why?!".isBig() // false! "harder, better, ...".isBig() // true! } // file MyUtils.java class MyUtils { static boolean isBig(String str) { return str.length() > 10; } } // file MyJavaClass.java class MyJavaClass { void example() { MyUtils.isBig("why?!"); MyUtils.isBig("harder, better, ..."); } } #9 Kotlin - Extensions http://kotlinlang.org/docs/reference/extensions.html vs
18. fun String.isBig(): Boolean { return length() > 10 } fun example() { "why?!".isBig() "harder, better, ...".isBig() } // file MyUtils.java class MyUtils { static boolean isBig(String str) { return str.length() > 10; } } // file MyJavaClass.java class MyJavaClass { void example() { MyUtils.isBig("why?!"); MyUtils.isBig("harder, better, ..."); } } #9 Kotlin - Extensions http://kotlinlang.org/docs/reference/extensions.html vs
19. class Hero(val power: Int) class Hero { private final int power; public Hero(int power) { this.power = power; } } #10 Kotlin - Infix Notation http://kotlinlang.org/docs/reference/functions.html#infix-notation vs
20. class Hero(val power: Int) { infix fun vs(opponent: Hero): Hero { return if (power > opponent.power) { this } else { opponent } } } #10 Kotlin - Infix Notation http://kotlinlang.org/docs/reference/functions.html#infix-notation vs
21. class Hero(val power: Int) { infix fun vs(opponent: Hero): Hero { return if (power > opponent.power) { this } else { opponent } } } fun example() { val thor = Hero(7) val ironman = Hero(8) val spiderman = Hero(4) } // Skip Java version of Hero class, // we use Kotlin class class MyJavaClass { void example() { Hero thor = new Hero(7); Hero ironman = new Hero(8); Hero spiderman = new Hero(4); } } #10 Kotlin - Infix Notation http://kotlinlang.org/docs/reference/functions.html#infix-notation vs
22. class Hero(val power: Int) { infix fun vs(opponent: Hero): Hero { return if (power > opponent.power) { this } else { opponent } } } fun example() { val thor = Hero(7) val ironman = Hero(8) val spiderman = Hero(4) val theBest = thor vs ironman vs spiderman } // Skip Java version of Hero class, // we use Kotlin class class MyJavaClass { void example() { Hero thor = new Hero(7); Hero ironman = new Hero(8); Hero spiderman = new Hero(4); Hero theBest = thor.vs(ironman).vs(spiderman); } } #10 Kotlin - Infix Notation http://kotlinlang.org/docs/reference/functions.html#infix-notation vs
23. class Hero(val power: Int) { infix fun vs(opponent: Hero): Hero { return if (power > opponent.power) { this } else { opponent } } } fun example() { val thor = Hero(7) val ironman = Hero(8) val spiderman = Hero(4) val theBest = thor vs ironman vs spiderman } // Skip Java version of Hero class, // we use Kotlin class class MyJavaClass { void example() { Hero thor = new Hero(7); Hero ironman = new Hero(8); Hero spiderman = new Hero(4); Hero theBest = thor.vs(ironman).vs(spiderman); } } #10 Kotlin - Infix Notation http://kotlinlang.org/docs/reference/functions.html#infix-notation vs
24. class Male(val eyes: String) class Female(val hair: String) class Male { private String eyes; public Male(String eyes) { this.eyes = eyes; } } class Female { private String hair; public Female(String hair) { this.hair = hair; } } #11 Kotlin - Operator Overloading http://kotlinlang.org/docs/reference/operator-overloading.html vs
25. class Male(val eyes: String) class Female(val hair: String) class Baby(val eyes: String, val hair: String) // Skip Java version of Male, Female and Baby // class, there is not enough space! #11 Kotlin - Operator Overloading http://kotlinlang.org/docs/reference/operator-overloading.html vs
26. class Male(val eyes: String) { operator fun plus(her: Female): Baby { return Baby(this.eyes, her.hair) } } class Female(val hair: String) class Baby(val eyes: String, val hair: String) // Skip Java version of Male, Female and Baby // class, there is not enough space! #11 Kotlin - Operator Overloading http://kotlinlang.org/docs/reference/operator-overloading.html vs
27. class Male(val eyes: String) { operator fun plus(her: Female): Baby { return Baby(this.eyes, her.hair) } } class Female(val hair: String) class Baby(val eyes: String, val hair: String) fun example() { val myBaby = Male("green") + Female("blond") } // Skip Java version of Male, Female and Baby // class, there is not enough space! class MyJavaClass { void example() { Baby myBaby = new Male("green").plus( new Female("blond")); } } #11 Kotlin - Operator Overloading http://kotlinlang.org/docs/reference/operator-overloading.html vs
28. class Male(val eyes: String) { operator fun plus(her: Female): Baby { return Baby(this.eyes, her.hair) } } class Female(val hair: String) class Baby(val eyes: String, val hair: String) fun example() { val myBaby = Male("green") + Female("blond") } // Skip Java version of Male, Female and Baby // class, there is not enough space! class MyJavaClass { void example() { Baby myBaby = new Male("green").plus(new Female("blond")); } } #11 Kotlin - Operator Overloading http://kotlinlang.org/docs/reference/operator-overloading.html vs
29. Android Example from REAL code!
30. Extensions // More examples (1) fun String.encodeUrl(charsetName: String = "UTF-8") = URLEncoder.encode(this, charsetName) fun String.isValidEmail() = Patterns.EMAIL_ADDRESS.matcher(this).matches() // INFO: https://en.wikipedia.org/wiki/Non-breaking_space fun String.useNonBreakingSpace() = replace(' ', '\u00A0') // http://developer.android.com/reference/android/content/Intent.html#ACTION_VIEW fun Uri.viewIntent() = Intent(Intent.ACTION_VIEW).setData(this) fun <T : View> T.onClick(onClick: (T) -> Unit) = setOnClickListener(onClick as (View) -> Unit) fun View.postDelayed(delayMillis: Long, action: () -> Unit) = postDelayed(action, delayMillis) val EditText.string: String get() = text.toString()
31. Extensions // More examples (2) fun View.hideSoftInput() { val imm = context.getSystemService(Context.INPUT_METHOD_SERVICE) as InputMethodManager imm.hideSoftInputFromWindow(windowToken, 0) } /** * Kotlin version of method Utils.isViewInBounds(container, view) by Alex Lockwood * URL: https://github.com/alexjlockwood/activity-transitions/blob/c4fa3a21c941691fb6bbe53e37cf3965842ee254/app/src/ main/java/com/alexjlockwood/activity/transitions/Utils.java * * Returns true if {@param view} is contained within {@param container}'s bounds. */ fun View.isInBounds(container: View): Boolean { val containerBounds = Rect() container.getHitRect(containerBounds) return getLocalVisibleRect(containerBounds) }
32. Extensions + Infix Notation // More examples infix fun String?.orNotNull(defaultValue: String): String = if (!this.isNullOrBlank()) this!! else defaultValue infix fun String?.or(defaultValue: String?): String? = if (!this.isNullOrBlank()) this else defaultValue // val a: String? = null // val b: String? = null // val c: String? = "test" // val myText = a or b or c orNotNull "default"
33. Extensions + Operator Overloading // More examples operator fun StringBuilder.plusAssign(s: String) { appendln(s) } // val sb = StringBuilder() // sb += "test" // sb += "test2"
34. Questions? Developers playground - #EX3 - In KotlinExample use: Extensions, Infix Notation, Operator Overloading Start with: https://github.com/jacklt/KotlinExample/tree/ex2 Solution: https://github.com/jacklt/KotlinExample/tree/ex3 (at some point maybe …) :P
35. THANKS! Omar Miatello, Member of GDG Milano (Italy) Android Developer @ Satispay