ANKO THE ULTIMATE NINJA OF KOTLIN LIBRARIES? AGENDA What are - - PowerPoint PPT Presentation

ANKO THE ULTIMATE NINJA OF KOTLIN LIBRARIES?

KAI KOENIG (@AGENTK)

AGENDA

▸ What are Kotlin and Anko? ▸ Anko-related idioms and language concepts ▸ Anko DSL ▸ The hidden parts of Anko ▸ Anko VS The Rest ▸ Final thoughts

WHAT ARE KOTLIN AND ANKO?

WHAT ARE KOTLIN AND ANKO?

SOME KOTLIN FUNDAMENTALS

▸ Statically typed programming

language for the JVM and Android

▸ Started as internal language “Project

Kotlin” at Jetbrains in 2010

▸ Now: Open-Source, Apache License ▸ Kotlin SDK plus tool support for IntelliJ,

Android Studio, Eclipse

▸ Named after an island in the Gulf of

Finland

WHAT ARE KOTLIN AND ANKO?

MOTIVATION FOR KOTLIN

▸ The Java platform is awesome, but it has its issues: ▸ sometimes tied to backwards/legacy compatibility ▸ can be a very verbose language and produce bloated code ▸ type system has various flaws ▸ Kotlin aims to fix a lot of those issues, in particular when you have to use Java 6

• r 7 (if we’re lucky…) and you can’t use all the new, shiny features from Java 8

and soon Java 9 and 10

WHAT ARE KOTLIN AND ANKO?

HOW DOES A SIMPLE CONVERSION LOOK LIKE?

public String listConvert(Collection<Integer> collection) { StringBuilder sb = new StringBuilder(); sb.append("{"); Iterator<Integer> iterator = collection.iterator(); while (iterator.hasNext()) { Integer element = iterator.next(); sb.append(element); if (iterator.hasNext()) { sb.append(", "); } } sb.append("}"); return sb.toString(); } fun listConvert(collection: Collection<Int>): String { val sb = StringBuilder() sb.append("{") val iterator = collection.iterator() while (iterator.hasNext()) { val element = iterator.next() sb.append(element) if (iterator.hasNext()) { sb.append(", ") } } sb.append("}") return sb.toString() } fun listConvertKt(collection: Collection<Int>): String { return collection.joinToString(prefix = "{",postfix = "}") }

WHAT ARE KOTLIN AND ANKO?

WHAT IS ANKO?

▸ Library to make Android development with Kotlin faster and easier ▸ Created by Jetbrains ▸ Best-known feature is Anko’s Layout DSL ▸ Some other functionality: ▸ intent and service wrappers ▸ async call handling ▸ SQLite

ANKO-RELATED IDIOMS & LANGUAGE PATTERNS

https://www.flickr.com/photos/geraldford/6976818221/

ANKO-RELATED IDIOMS & LANGUAGE PATTERNS

IDIOM AND LANGUAGE OVERVIEW

▸ Immutability ▸ String templates & Enum classes ▸ Null safety ▸ Properties and Fields ▸ Type inference and casts ▸ Data classes ▸ Syntactic sugar (loops, ranges etc) ▸ Extension functions ▸ Lambdas ▸ Collection API ▸ Type-safe builders ▸ Java-Kotlin-Interop

ANKO-RELATED IDIOMS & LANGUAGE PATTERNS

DATA CLASSES

▸ The POJOs or Beans of other languages ▸ Data classes implicitly create: ▸ getters/setters (non-data classes have

those too) - recommended to use val as often as possible.

▸ proper and useful implementations for

equals(), hashCode(), toString(), copy()

▸ copy() has default parameters and can

be used to alter a copy

data class ChromeEncryptedPayload( val encryptedPayload: String, val encryptionHeader: String, val cryptoKeyHeader: String)

ANKO-RELATED IDIOMS & LANGUAGE PATTERNS

PROPERTIES AND FIELDS

▸ Kotlin classes have mutable or

immutable properties

▸ An automated backing field can be

provided by the compiler (if required)

▸ Default getter/setters for properties,

can be customised

var counter = 0 set(value) { if (value >= 0) field = value }

ANKO-RELATED IDIOMS & LANGUAGE PATTERNS

EXTENSION FUNCTIONS

▸ Allow adding new functionality to a

class without inheritance or decorators

▸ Kotlin has extension functions as well

as extension properties

▸ Resolved statically, don’t actually

modify the class (excellent example why this has to be the case at http:// goo.gl/EN6bTs)

fun Int.sum(otherInt: Int): Int = this +

• therInt

3.sum(7) fun Activity.toast(message: CharSequence, duration: Int = TOAST.LENGTH_SHORT) { Toast.makeText(this, message, duration).show() } // In onCreate of an Activity

• verride fun onCreate(...) {

... toast("Hi there") ... }

ANKO-RELATED IDIOMS & LANGUAGE PATTERNS

TYPE-SAFE BUILDERS (I)

▸ Builders are a very popular approach in

Groovy to define data in a declarative way

▸ Often used for: ▸ generating XML or JSON ▸ UI layout (Swing components) etc ▸ In Kotlin, builders even can be type-

checked

JsonBuilder builder = new JsonBuilder() builder.records { car { name 'HSV Maloo' make 'Holden' year 2006 country 'Australia' } } String json = JsonOutput.prettyPrint (builder.toString())

ANKO-RELATED IDIOMS & LANGUAGE PATTERNS

TYPE-SAFE BUILDERS (II)

▸ html() is a function with a lambda as an

argument (init)

▸ init’s type is a function type with

receiver, this allows you to:

▸ pass receiver (of type HTML) to

function

▸ call members of instance inside the

function

fun result(args: Array<String>) = html { head { title {”HTML in Kotlin"} } body { ... } } fun html(init: HTML.() -> Unit): HTML { val html = HTML() html.init() return html }

ANKO-RELATED IDIOMS & LANGUAGE PATTERNS

TYPE-SAFE BUILDERS (III)

▸ Html class has functions to build the

head and the body elements of the DSL.

▸ Not shown: classes further down in the

hierachy:

▸ Head, Body etc. ▸ Complete HTML builder example at:

http://goo.gl/TndcC9

class Html { ... fun head(headBuilder: Head.() -> Unit) { head = Head() head?.headBuilder() } fun body(bodyBuilder: Body.() -> Unit) { body = Body() body?.bodyBuilder() } }

ANKO-RELATED IDIOMS & LANGUAGE PATTERNS

IDIOM AND LANGUAGE OVERVIEW

▸ Immutability ▸ String templates & Enum classes ▸ Null safety ▸ Properties and Fields ▸ Type inference and casts ▸ Data classes ▸ Syntactic sugar (loops, ranges etc) ▸ Extension functions ▸ Lambdas ▸ Collection API ▸ Type-safe builders ▸ Java-Kotlin-Interop

ANKO DSL

ANKO DSL

WHAT IS A DSL?

▸ Domain-Specific Language

▸ Computer programming language ▸ Limited expressiveness: ▸ DSLs are usually not general-purpose languages ▸ strongly focussed on a particular domain ▸ examples: SQL, Ant XML, XSLT, Gradle etc.

ANKO DSL

MORE ON DSL CONCEPTS

▸ Increased level of abstraction ▸ What vs. How ▸ Common discussion: are DSLs code or data? ▸ Interpretation vs. code generation

ANKO DSL

A DSL FOR LAYOUTS

▸ The most important element of Anko is the Layout DSL ▸ Idea: replace XML layout definitions by Kotlin code - without having to build

the layout in a fully programmatic sense

▸ Modular: as we’re talking about UI/Layout, it’s very important to select the

right library for your minSDKVersion

▸ Extensible: you can add your own DSL elements for custom UI controls

ANKO DSL

LAYOUT XML

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="match_parent" android:layout_height="match_parent"> <EditText android:layout_width="match_parent" android:gravity="center" android:text="@string/empty_todos_message" android:layout_weight="7" android:layout_height="wrap_content" /> <Button android:layout_width="match_parent" android:layout_weight="1" android:text="Say Hello" android:layout_height="0dp" /> </LinearLayout>

ANKO DSL

PROGRAMMATIC LAYOUT IN KOTLIN

val act = this val layout = LinearLayout(act) layout.orientation = LinearLayout.VERTICAL val name = EditText(act) val button = Button(act) button.text = "Say Hello" button.setOnClickListener { Toast.makeText(act, "Hello, ${name.text}!", Toast.LENGTH_SHORT).show() } layout.addView(name) layout.addView(button)

ANKO DSL

ANKO DSL

verticalLayout { val name = editText() button("Say Hello") {

• nClick { toast("Hello, ${name.text}!") }

} }

ANKO DSL

ANKO DSL INTERNALS

▸ Anko DSL example from previous slide looks very similar to the earlier HTML

builder example

▸ Anko uses extension functions arranged into type-safe builders and lambdas ▸ You don’t have to write all those extensions by hand though - Anko generates

them based on the Android SDK’s android.jar

ANKO DSL

GETTING STARTED WITH ANKO DSL (I)

▸ Depending on minSdkVersion of project, import:


compile "org.jetbrains.anko:anko-sdk{15|19|21|23}:0.9"

▸ If the project uses an Android Support library, import matching Anko library:


compile “org.jetbrains.anko:anko-recyclerview-v7:0.9"

ANKO DSL

GETTING STARTED WITH ANKO DSL (II)

▸ General approach: ▸ Anko DSL automatically becomes

available in onCreate() in an Activity

▸ no need for setContentView(), Anko

DSL also automatically sets the content view for activities

• verride fun onCreate(savedInstanceState: Bundle?) {

super.onCreate(savedInstanceState) verticalLayout { padding = dip(30) editText { hint = "Name" textSize = 24f } editText { hint = "Password" textSize = 24f } button("Login") { textSize = 26f } } }

ANKO DSL

ANKO DSL IN FRAGMENTS

▸ In fragments, use 


• nCreateView(…)

▸ Returns UI {…}.view: ▸ mandatory before Anko 0.8 ▸ works well for Fragments ▸ createTodo() is a fragment-private

method

• verride fun onCreateView(inflater: LayoutInflater?,

container: ViewGroup?, savedInstanceState: Bundle?): View? { return UI { verticalLayout { padding = dip(24) var title = editText { id = R.id.title hintResource = R.string.hint } ... button { id = R.id.add textResource = R.string.add

• nClick { view -> createTodo(title, desc) }

} } }.view }

ANKO DSL

ANKO COMPONENTS (I)

▸ Often it’s nicer to have UI code separated from onCreate or other livecycle

methods

▸ AnkoComponent helps organising your UI code in their own classes

ANKO DSL

ANKO COMPONENTS (II)

class EditFragmentUI : AnkoComponent<EditFragment> {

• verride fun createView(ui: AnkoContext<EditFragment>) = with(ui) {

verticalLayout { padding = dip(24) var title = editText { id = R.id.title hintResource = R.string.hint } ... button { id = R.id.add textResource = R.string.add

• nClick { view -> ui.owner.createTodoFrom(title, desc) }

} } } }

• verride fun onCreateView(...)= EditFragmentUI().createView(AnkoContext.create(ctx,this))

ANKO DSL

ANKO COMPONENTS (III)

▸ Anko Preview plugin for

AnkoComponent layouts

▸ Get it here: http://goo.gl/5CVmAA ▸ Can preview layouts and convert XML

to Anko DSL

▸ Can be fiddly to get going with AS,

Kotlin plugin versions

ANKO DSL

EXTENDING ANKOS DSL FUNCTIONALITY (I)

▸ Multiple ways to do this: ▸ insert an existing XML layout into an Anko DSL declaration:
 ▸ adding new DSL elements to the language

include<View>(R.layout.mylayout) { ... } inline fun ViewManager.customView(theme: Int = 0) = customView(theme) {} inline fun ViewManager.customView(theme: Int = 0, init: CustomView.() -> Unit) = ankoView({ CustomView(it) }, theme, init) inline fun Activity.customView(theme: Int = 0) = customView(theme) {} inline fun Activity.customView(theme: Int = 0, init: CustomView.() -> Unit) = ankoView({ CustomView(it) }, theme, init)

ANKO DSL

EXTENDING ANKOS DSL FUNCTIONALITY (II)

▸ Extending Anko’s DSL to support your own custom view groups is currently rather

painful

▸ Essentially it comes down to .lparams (for layout purposes) not being easily accessible ▸ More here: ▸ http://goo.gl/qpb3SL ▸ http://goo.gl/tMHs2c ▸ Fix targeted for Anko 0.9.1

THE HIDDEN PARTS OF ANKO

THE HIDDEN PARTS OF ANKO

BUT THERE’S MORE

▸ Intent wrappers for various purposes: e.g. sendSMS(number, [text]) ▸ Intent builders ▸ Service shortcuts ▸ Configuration qualifiers: configuration(screenSize = ScreenSize.LARGE,

• rientation = Orientation.LANDSCAPE) { … }

▸ Asynchronous tasks ▸ SQLLite

THE HIDDEN PARTS OF ANKO

INTENT WRAPPERS AND SERVICE SHORTCUTS

▸ Anko provides wrappers for commonly used Intents: ▸ makeCall(number), sendSMS(number, text), browse(url) etc. ▸ Shortcuts to Android services: ▸ notificationManager, displayManager, sensorManager etc. ▸ Useful, but both not major features of Anko

THE HIDDEN PARTS OF ANKO

INTENT BUILDERS

▸ Syntactic sugar to cut down the amount of code needed to start a new activity

val intent = Intent(this, javaClass<MyActivity>()) intent.putExtra("customerId", 4711) intent.putExtra("country", "NZ") startActivity(intent) startActivity(Intent(this, MyActivity::class.java). putExtra("customerId", 4711).putExtra("country", "NZ")) startActivity<MyActivity>("customerId" to 4711, "country" to "NZ")

THE HIDDEN PARTS OF ANKO

CONFIGURATION QUALIFIERS

▸ “CSS Media Queries for Android” ▸ Screen features: ▸ screenSize, density, orientation, long, 


nightMode, rightToLeft, smallestWidth

▸ SDK versions: ▸ fromSdk, sdk ▸ Other: ▸ language, uiMode

configuration(screenSize = ScreenSize.LARGE,

• rientation =

Orientation.LANDSCAPE) { /* This code will be only executed if the screen is large and its

• rientation is landscape

*/ }

THE HIDDEN PARTS OF ANKO

ASYNC DSL

▸ Does anyone enjoy working with AsyncTasks? ▸ Anko: async and asyncResult (return future respectively future with result)

async() { val result = PetFindCommand("90210","cat").execute() uiThread { animalList.adapter = AnimalListAdapter(result,

• bject: AnimalListAdapter.ItemClickListener{
• verride fun invoke(pet:Pet) {

toast(pet.name) } } ) } }

THE HIDDEN PARTS OF ANKO

SQLITE (I)

▸ Working with SQLite usually requires a lot of boilerplate code and try/catch-

structures, issues around concurrency, dealing with cached code and references etc.

▸ Anko aims to make that easier ▸ Dependency: compile ‘org.jetbrains.anko:anko-sqlite:0.9' ▸ Setup class extending ManagedSQLiteOpenHelper in your code

THE HIDDEN PARTS OF ANKO

SQLITE (II)

▸ database.use ensures DB is opened

and closed correctly

▸ Asynchronous use of the DB is possible

through Anko’s async DSL

▸ Important: There can still be

SQLiteExceptions when handling SQL code - Anko doesn’t abstract those.

▸ Handling of cursors and parsing data

via lambdas

database.use { createTable("Customer", ifNotExists = true, "id" to INTEGER + PRIMARY_KEY + UNIQUE, "name" to TEXT, "photo" to BLOB) }

ANKO VS THE REST?

https://www.flickr.com/photos/sillygwailo/5990089210/

ANKO VS THE REST?

ANKO AND OTHER KOTLIN LIBRARIES

▸ KAndroid ▸ Kovenant

ANKO VS THE REST?

KANDROID

▸ KAndroid is an extension library for Kotlin/Android ▸ Contains a variety of absolutely distinct and unconnected functionality ▸ Common theme: let’s get rid of boilerplate code ▸ Apache 2.0 license

ANKO VS THE REST?

KANDROID FEATURES

▸ View binding (again) ▸ TextWatcher ▸ SeekBar Extension ▸ SearchView Extension ▸ Shortcuts to system services ▸ Logging ▸ Dealing with Intents ▸ SDK Version API (from/to) ▸ Thread management

ANKO VS THE REST?

KANDROID EXAMPLES

runDelayed(1000) { // delayed execution } runDelayedOnUiThread(5000) { // delayed UI update } toApi(16, inclusive = true) { // handle devices running older APIs }

ANKO VS THE REST?

KOVENANT

▸ In a nutshell: Promises for Kotlin ▸ Very modular built, you can essentially pick and choose the artifacts of

Kovenant you’d like to use - Kovenant is not an Android-specific library

▸ Good starting set for Android: core, android, combine, jvm, functional ▸ MIT license

ANKO VS THE REST?

KOVENANT FEATURES

▸ Core, foundations of a promise

framework

▸ Tasks & callbacks ▸ Chaining (Then, ThenApply) ▸ Lazy promises ▸ Cancelling and voiding ▸ Combine: combines 2-20 promises ▸ Functional: adds map, bind and

apply to support more advanced HOF constructs in Kovenant

▸ JVM: Executors and Throttles (thread

pools)

▸ Android: UI callbacks and interacting

with UI Thread

ANKO VS THE REST?

KOVENANT EXAMPLES (I)

task { // some long-running thing } success { println("result: $it") } fail { println("problem: ${it.message}") } always { // this will always happen }

ANKO VS THE REST?

KOVENANT EXAMPLES (II)

promiseOnUi { // do some UI preparation } then { // the actual work } successUi { // update UI }

FINAL THOUGHTS

https://www.flickr.com/photos/brickset/16099265973/

FINAL THOUGHTS

MATURITY AND FUTURE

▸ Kotlin 1.0 was a big step for the language ▸ Surprisingly mature for a 1.0 release (but 5+ years in the making), full of great

concepts and idioms, getting better with each release

▸ Anko is very stable given it’s still a 0.x release ▸ Anko makes UI declaration actually pleasurable but offers way more than only a

layout DSL

▸ KAndroid offers additional extension functions, Kovenant is a full-on promises

framework

FINAL THOUGHTS

WHAT DID WE COVER?

▸ What are Kotlin and Anko? ▸ Anko-related idioms and language concepts ▸ Anko DSL ▸ The hidden parts of Anko ▸ Anko VS The Rest ▸ Final thoughts

FINAL THOUGHTS

RESOURCES

▸ Kotlin: http://kotlinlang.org ▸ Anko: https://github.com/Kotlin/anko ▸ Fuel: https://github.com/kittinunf/Fuel ▸ KAndroid: https://github.com/pawegio/KAndroid ▸ Kovenant: https://github.com/mplatvoet/kovenant

FINAL THOUGHTS

GET IN TOUCH

Kai Koenig Email: kai@ventego-creative.co.nz Twitter: @AgentK