kotlin a problem solver - gdd extended pune

Kotlin for AndroidA Real Problem Solver

Hardik Trivedi

Source : https://developers.google.com/events/gdd-india/

Hardik Trivedi● I am a computer program writer

● Works at Globant, Pune, IN

● An active community speaker

● Co-author of a book "Kotlin Blueprints"

● I love writing tech blogs

● I am mentor for college graduates and

professionals and consultant to companies

About MeEmail: [email protected] Follow: @MrHardikTrivedi Visit: trivedihardik.wordpress.com

Exciting talk and training from Sean @ GDDIndiaEmail: [email protected] Follow: @MrHardikTrivedi Visit: trivedihardik.wordpress.com

Day 1: Testing Out Kotlin

Testing is a great way to learn Kotlin, write readable tests, and introduce your development team to the power of Kotlin. Learn how to use Kotlin through a deep dive into writing tests.

Day 2: Taking Advantage of Kotlin in Your Android App

Hands-on experience building Android apps using Android Studio in the Kotlin language.Checkout code at https://goo.gl/SyGJ1i

Sean McQuillanAndroid Developer

@ Google

https://goo.gl/SyGJ1i

Why Kotlin?Email: [email protected] Follow: @MrHardikTrivedi Visit: trivedihardik.wordpress.com

It’s a Modern

● Type Inference

● First class functions

● Abstraction

● Lambdas

● Extensions

● Coroutines


It’s built for Industry

● Not only expressive but keeps Performance in mind

● Readable

● Easy to write scalable code

● It’s targeting JVM, mobile and browsers

● Great tooling support from JetBrains


It’s easy to Use

● Interoperability

● Learn in a day

● No surprises

Kotlin announcementsEmail: [email protected] Follow: @MrHardikTrivedi Visit: trivedihardik.wordpress.com

● Kotlin 1.2 is out. It has ability to reuse code between JVM and JavaScript

● Kotlin/Native 0.5 is out and it has power calling Kotlin from Swift, C and LLVM 5

● Added a style guide https://android.github.io/kotlin-guides/style.html It has all

the standards Google has used to code in Kotlin

● Added Kotlin/Native support to CLion

● Jetbrains release official Kotlin wrappers to work with React.JS

● Android Lint has support to Kotlin. You can also write custom lint rules for Kotlin.

https://android.github.io/kotlin-guides/style.html

KotlinBasics.inc(){ }


Extension FunctionEmail: [email protected] Follow: @MrHardikTrivedi Visit: trivedihardik.wordpress.com

val str = "GGDD Extendedd"

fun String.removeFirstLastChar(): String {

return this.substring(1, this.length - 1)

}

str.removeFirstLastChar()// Output is GDD Extended

Extension FunctionEmail: [email protected] Follow: @MrHardikTrivedi Visit: trivedihardik.wordpress.com

fun View.visible() {

this.visibility = View.VISIBLE

}

fun View.gone() {

this.visibility = View.GONE

}

button.visible()

textView.gone()

Delegated PropertiesEmail: [email protected] Follow: @MrHardikTrivedi Visit: trivedihardik.wordpress.com

Properties usually contains the direct corresponding value

But Kotlin allows you to delegate some task/behaviour to the properties if managed

properly.

● lazy properties: the value gets computed only upon first access;

● observable properties: listeners get notified about changes to this property;

● storing properties in a map, instead of a separate field for each property.

Delegated Properties - VetoableEmail: [email protected] Follow: @MrHardikTrivedi Visit: trivedihardik.wordpress.com

class Veto {

var value: String by Delegates.vetoable("String")

{ prop, old, new -> new.contains("GDD") }

}

val veto = Veto()

veto.value = "DevFest"

println(veto.value) // Output String

veto.value="GDD Extended Pune"

println(veto.value) // Output GDD Extended Pune

Semantic ValidationEmail: [email protected] Follow: @MrHardikTrivedi Visit: trivedihardik.wordpress.com

Many times we do parameter validation thorough and aggressivelystatic String join(String sep, List<String> strings) {

if (sep == null) throw new NullPointerException("sep == null");

if (sep.length() < 2) {

throw new IllegalArgumentException("sep.length() < 2");

}

if (strings == null) throw new NullPointerException("strings == null");

...

}

Semantic ValidationEmail: [email protected] Follow: @MrHardikTrivedi Visit: trivedihardik.wordpress.com

● With Guava like libraries you can avoid those null checks and manage the pre

conditions gracefully.

● But you don’t add guava for to use only one feature.

● Kotlin avoids nullability by default and it has functions for semantic validations.

fun join(sep: String, strings: List<String>): String {

require(sep.length < 2) { "sep.length() < 2" }

...

}

Let functionEmail: [email protected] Follow: @MrHardikTrivedi Visit: trivedihardik.wordpress.com

Java

String data=null;

if(data!=null) {

// Do something

}

Kotlin

var data: String? = null

data?.let {

// it == data always not null and read only once

}

Let functionEmail: [email protected] Follow: @MrHardikTrivedi Visit: trivedihardik.wordpress.com

class Concurrent {

@Volatile var data: String? = null

fun doSomething() {

data?.let {

//data always not null and read only once

}

}

}

Higher-order functionEmail: [email protected] Follow: @MrHardikTrivedi Visit: trivedihardik.wordpress.com

A higher-order function is a function that takes functions as parameters, or returns a

function.

fun logExecution(func: () -> Unit) {

Log.d("tag", "before executing func")

func()

Log.d("tag", "after executing func")

}

logExecution({ yourFunction() })

Wow momentsSee Kotlin in Action !!!{ }


Wow momentsEmail: [email protected] Follow: @MrHardikTrivedi Visit: trivedihardik.wordpress.com

// Possible only if it's Java 8

public interface InterfaceA {

default void defaultMethod(){

System.out.println("Interface A

default method");

}

}

interface ToolbarManager {

fun initToolbar() {

toolbar.inflateMenu(R.menu.main_menu)

toolbar.setOnMenuItemClickListener {

// Your code

true

}

}

}

Java Kotlin


Button clickButton = (Button)

findViewById(R.id.clickButton);

clickButton.setOnClickListener( new

OnClickListener() {

@Override

public void onClick(View v) {

***Do what you want with the

click here***

}

});

import

kotlinx.android.synthetic.main.activity_

detail.*

clickButton.setOnClickListener {

***Do what you want with the click

here***

}

Java Kotlin


private String readInputStream(InputStream is) throws

Exception {

String line = null;

StringBuilder sb = new StringBuilder();

BufferedReader bufferedReader = new

BufferedReader(new InputStreamReader(is));

while ((line = bufferedReader.readLine()) != null)

{

sb.append(line);

}

bufferedReader.close();

return sb.toString();

}

val inputAsString =

is.bufferedReader().use

{ it.readText() }

// defaults to UTF-8

Java Kotlin

Wow moments

public class MySingleton {

private static MySingleton myObj;

private MySingleton(){

}

public static MySingleton getInstance(){

if(myObj == null){

myObj = new MySingleton();

}

return myObj;

}

}

object MySingleton {

var num: Int = 0

fun domeSomeThing() {

println("Kotlin is awesome!!!")

}

}

Java Kotlin

Email: [email protected] Follow: @MrHardikTrivedi Visit: trivedihardik.wordpress.com


SharedPreferences sharedpreferences =

getSharedPreferences(mypreference,

Context.MODE_PRIVATE);

email.setText(sharedpreferences.getStrin

g(Email, ""));

SharedPreferences.Editor editor =

sharedpreferences.edit();

editor.putString("email",

"[email protected]");

editor.apply();

private var email: String by

DelegatedPreference(this, "email", "")

email="[email protected]"

txtEmail.text=email

Java Kotlin


Movie movie = moviesList.get(position);

holder.title.setText(movie.getTitle());

holder.genre.setText(movie.getGenre());

holder.year.setText(movie.getYear());

Movie movie = moviesList[position]

with(movie) {

holder.title.text=title

holder.genre.text=genre

holder.year.text=year

}

Java Kotlin


private class GetWeatherTask extends

AsyncTask<String, Void, Forecast> {

protected Forecast doInBackground(String

zipCode) {

return WeatherAPI().execute(zipCode);

}

protected void onPostExecute(Forecast

result) {

showData(result);

}

}

new GetWeatherTask().execute(380015);

fun loadWeatherData() = async(UI) {

val waiter = bg {

WeatherApi(zipCode).execute() }

showData(waiter.await())

}

Java Kotlin


Intent intent = Intent(this,SomeOtherActivity.class)

intent.putExtra("id", 5)

intent.setFlag(Intent.FLAG_ACTIVITY_SINGLE_TOP)

startActivity(intent)

startActivity(intentFor<SomeOtherActivity>("id" to 5).singleTop())

Java

Kotlin


public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle

savedInstanceState) {

return inflater.inflate(R.layout.fragment_update_info, container, false);

}

fun ViewGroup.inflate(@LayoutRes layoutRes: Int, attachToRoot: Boolean = false):

View {

return LayoutInflater.from(context).inflate(layoutRes, this, attachToRoot)

}

parent.inflate(R.layout.my_layout)

parent.inflate(R.layout.my_layout, true)

Java

Kotlin


Picasso.with(context).load(R.mipmap.ic_launcher).into(imageView);

fun ImageView.loadUrl(url: String) {

Picasso.with(context).load(url).into(this)

}

imageView.loadUrl("http://....")

Java

Kotlin


getSupportFragmentManager().beginTransaction()

.add(R.id.container,DataFragment.newInstance(), "detail")

.addToBackStack()

.commit();

fun AppCompatActivity.addFragment(fragment: Fragment, frameId: Int, backStackTag: String? =

null) {

supportFragmentManager.inTransaction {

add(frameId, fragment)

backStackTag?.let { addToBackStack(fragment.javaClass.name) }

}

}

addFragment(DataFragment.newInstance(), R.id.container, "detail")

Java

Kotlin

Snackbar snackbar = Snackbar

.make(coordinatorLayout, "Welcome to GDD", Snackbar.LENGTH_LONG);

snackbar.show();

inline fun View.snack(message: String, length: Int = Snackbar.LENGTH_LONG) {

val snack = Snackbar.make(this, message, length)

snack.show()

}

view.snack("Welcome to GDD")

view.snack("Welcome to GDD", Snackbar.LENGTH_SHORT)

Java

Kotlin


class Address {

String name = ...;

String street = ...;

String city = ...;

String state = ...;

String zip = ...;

}

Address address = new Address();

System.out.println(address.getName());

System.out.println(address.getStreet());

class Address {

var name: String = ...

var street: String = ...

var city: String = ...

var state: String? = ...

var zip: String = ...

}

val address = Address()

println(address.name)

println(address.street)

Java Kotlin


scrollView.postDelayed(new Runnable() {

@Override

public void run() {

doSomething(position);

}

}, 250);

scrollView.postDelayed({

onTabPageSelected(position) }, 200)

Java Kotlin



List<User> users = api.getUsers();

List<User> activeUsers = new

ArrayList<>();

for (User user : users) {

if (user.isActive()) {

activeUsers.add(user);

}

}

adapter.setUsers(activeUsers);

val users = api.getUsers()

val activeUsersNames = items.filter {

it.active

}

adapter.setUsers(activeUsers)

Java Kotlin



private class GetWeatherTask extends

AsyncTask<String, Void, Forecast> {

protected Forecast doInBackground(String

zipCode) {

return WeatherAPI().execute(zipCode);

}

protected void onPostExecute(Forecast

result) {

showData(result);

}

}

new GetWeatherTask().execute(380015);

fun loadWeatherData() = async(UI) {

val waiter = bg {

WeatherApi(zipCode).execute() }

showData(waiter.await())

}

Java Kotlin


@Override

public boolean onOptionsItemSelected(MenuItem

item) {

switch (item.getItemId()) {

case R.id.new_game:

newGame();

return true;

case R.id.help:

showHelp();

return true;

default:

return

super.onOptionsItemSelected(item);

}

}

override fun onOptionsItemSelected(item:

MenuItem) = when (item.itemId) {

R.id.new_game -> consume {

navigateToNewGame() }

R.id.help -> drawer.consume {

navigateToHelp() }

else -> super.onOptionsItemSelected(item)

}

inline fun consume(f: () -> Unit): Boolean {

f()

return true

}

Java Kotlin


if (obj instanceof TextArea) {

((TextArea)obj).append("some data");

} else {

// Do something

}

if (view is TextArea) {

view.append("Kotlin is awesome!")

} else {

// Do something

}

Java Kotlin



textView {

id = R.id.errorView

textColor = ContextCompat.getColor(ctx, R.color.red_error)

text = string(R.string.error_view_login_text)

textSize = 14f

visibility = View.GONE

}

textView {

lparams(width = matchParent, height = wrapContent) {

gravity = Gravity.CENTER

leftMargin = dip(16)

rightMargin = dip(16)

}

}



// Showing Alerts

alert("Hi, are you enjoying the Kotlin talk?") {

yesButton { toast("Yes :)") }

noButton {}

}.show()

// Showing progress dialog

val dialog = progressDialog(message = "Please wait a bit…", title = "Fetching data")

// Showing SnackBar

snackbar(view, "Hi there!")

snackbar(view, R.string.message)

longSnackbar(view, "Wow, such duration")

snackbar(view, "Action, reaction", "Click me!") { doStuff() }


anObservable

.subscribeOn(Schedulers.io())

.observeOn(AndroidSchedulers.mainThread())

.map(new Func1<String, List<String>>() {

@Override

public List<String> call(String s) {

...

}

})

.subscribe(new Observer<List<String>>() {

...

anObservable

.subscribeOn(Schedulers.io())

.observeOn(AndroidSchedulers.mainThread(

))

.map { }

.doOnNext{ }

.subscribe { data -> }

Java Kotlin


@Test

public void

testSomethingWorksAsExpected() {

Assert.assertTrue(false);

}

Java@Test fun `test something works as

expected`() {

Assert.assertTrue(false)

}

Also

import org.mockito.Mockito.`when` as

_when

Kotlin



JVM Native

iOS, etc.

JS

Kotlin

Android Spring, etc.

Future of KotlinEmail: [email protected] Follow: @MrHardikTrivedi Visit: trivedihardik.wordpress.com

ReferencesEmail: [email protected] Follow: @MrHardikTrivedi Visit: trivedihardik.wordpress.com

● Kotlin official website

● Android official website

● Git repo from Developer Advocate at JetBrains

● Android Pub

● Antonio Leiva's blog

● Bob’s blog

● Anko Github page

● Sample Android app using Kotlin

ReferencesEmail: [email protected] Follow: @MrHardikTrivedi Visit: trivedihardik.wordpress.com

https://kotlinlang.org/

https://developer.android.com/index.html

https://github.com/hhariri/oreilly-kotlin-course

https://android.jlelse.eu/

https://antonioleiva.com/kotlin/

https://medium.com/thoughts-overflow

https://github.com/Kotlin/anko

https://github.com/hardik-trivedi/GDG_Pune_Kotlin_Workshop

Thank You@MrHardikTrivedi{ }


kotlin a problem solver - gdd extended pune

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