android & kotlin - the code awakens #03
TRANSCRIPT
Android & KotlinThe code awakens #03
Omar MiatelloMember of GDG Milano (Italy)Android Developer @ Satispay
Personal profilegoogle.com/+OmarMiatelloGoogle+ Community: Kotlin for Androidgoo.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
dummy/HeroAdapter.javapublic 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)
Previously on Android & Kotlin #01: goo.gl/0jHLmEProperties
val a: Int = 1 // val = READ ONLY (getter)var b: Int = 1 // var = READ/WRITE (getter/setter)
String templates"My name is $name $surname"
Lambdasview.setOnClickListener { Log.d("TAG", "Item clicked!") }
Delegated properties (example: lazy)val item by lazy { MyItem() }
// val = READ ONLY (getter)// var = READ/WRITE (getter/setter)
val onlyRead = 1var writable = 2var 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
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: ${System.currentTimeMillis()}ms since 1970"}
String templates // More examples
"qwerty | 123 | abc".filter { char -> char.isDigit() // return is implicit in lambda expressions}
"qwerty | 123 | abc".filter { it.isDigit() // we can use "it" with 1 parameter}
"qwerty | 123 | abc".filterIndexed { index: Int, c: Char -> index > 3 && c.isLetterOrDigit()}
Lambdas // More examples
val startTime by lazy { System.currentTimeMillis() }
var test by Delegates.observable(3) { prop, old, new -> if (new > old) Log.w("TEST", "$new > $old")}
fun test() { startTime test = 5 test = 1 test = 2 val finish = System.currentTimeMillis() - startTime}
Delegated properties // More examples
Previously on Android & Kotlin #02: goo.gl/h3uG8M
Null safety var a: String = null // Error at compile timevar b: String? = null
Elvis Operatorval example: String = b ?: "Default" // b may be null
Smart-castif (myView is TextView) { myView.setText("Ciao") }
CollectionslistOf("Android", "iOS", null).filterNotNull().map { it.toUpperCase() }
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
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
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
Kotlin vs Java - Part 3Extensions
Infix NotationOperator Overloading
fun String.isBig(): Boolean { return length() > 10}
#9 Kotlin - Extensionshttp://kotlinlang.org/docs/reference/extensions.html
vs
fun String.isBig(): Boolean { return length() > 10}
fun example() { "why?!".isBig() // false! "harder, better, ...".isBig() // true!}
#9 Kotlin - Extensionshttp://kotlinlang.org/docs/reference/extensions.html
vs
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 - Extensionshttp://kotlinlang.org/docs/reference/extensions.html
vs
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 - Extensionshttp://kotlinlang.org/docs/reference/extensions.html
vs
class Hero(val power: Int) class Hero { private final int power;
public Hero(int power) { this.power = power; }}
#10 Kotlin - Infix Notationhttp://kotlinlang.org/docs/reference/functions.html#infix-notation
vs
class Hero(val power: Int) { infix fun vs(opponent: Hero): Hero { return if (power > opponent.power) { this } else { opponent } }}
#10 Kotlin - Infix Notationhttp://kotlinlang.org/docs/reference/functions.html#infix-notation
vs
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 Notationhttp://kotlinlang.org/docs/reference/functions.html#infix-notation
vs
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 Notationhttp://kotlinlang.org/docs/reference/functions.html#infix-notation
vs
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 Notationhttp://kotlinlang.org/docs/reference/functions.html#infix-notation
vs
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 Overloadinghttp://kotlinlang.org/docs/reference/operator-overloading.html
vs
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 Overloadinghttp://kotlinlang.org/docs/reference/operator-overloading.html
vs
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 Overloadinghttp://kotlinlang.org/docs/reference/operator-overloading.html
vs
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 Overloadinghttp://kotlinlang.org/docs/reference/operator-overloading.html
vs
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 Overloadinghttp://kotlinlang.org/docs/reference/operator-overloading.html
vs
Android Examplefrom REAL code!
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_spacefun String.useNonBreakingSpace() = replace(' ', '\u00A0')
// http://developer.android.com/reference/android/content/Intent.html#ACTION_VIEWfun 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()
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)}
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"
Extensions + Operator Overloading // More examples
operator fun StringBuilder.plusAssign(s: String) { appendln(s) }
// val sb = StringBuilder()// sb += "test"// sb += "test2"
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
THANKS!Omar Miatello, Member of GDG Milano (Italy)
Android Developer @ Satispay