eMan Dev Meetup: Kotlin For Android (part 03/03) 18.5.2017

Kotlin for Android
Overview:
● Kotlin & Android
● Kotlin Android Extensions
● Anko
● Requery
● Kotpref
● PaperParcel

Kotlin for Android
● Reduce the amount of boilerplate code you need to write
● Make your code more readable and understandable
● No more errors such as NPE
● No more findViewById()
● One language for Android & Gradle
● Interoperability
● New languge -> Kotlin is fun
● Compatible with JDK 6 -> can run on older Android devices

Kotlin for Android / Android Extensions
Kotlin Android Extensions
● Compiler extension that allows to us replace findViewById() calls with
synthetic-generated properties

Example:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
tools:context="cz.kotliners.android.extension.demo.MainActivity">
<TextView
android:id="@+id/helloText"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
</LinearLayout>

Example:
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
}
private TextView helloText;
helloText = (TextView) findViewById(R.id.helloText);
helloText.setText("Hello World!");

Example:
Add Kotlin Android Extensions Gradle plugin:
// app/build.gradle
apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'

Example:
class MainActivityKotlin : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
}
}
helloText.setText("Hello CZ KUG!!!")
import kotlinx.android.synthetic.main.activity_main.*

Example:
public final class MainActivityKotlin extends AppCompatActivity {
private HashMap _$_findViewCache;
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
this.setContentView(2130968603);
((TextView)this._$_findCachedViewById(id.helloText)).setText((CharSequence)"Hello CZ KUG!!!");
}
public View _$_findCachedViewById(int var1) {
if(this._$_findViewCache == null) {
this._$_findViewCache = new HashMap();
}
View var2 = (View)this._$_findViewCache.get(Integer.valueOf(var1));
if(var2 == null) {
var2 = this.findViewById(var1);
this._$_findViewCache.put(Integer.valueOf(var1), var2);
}
return var2;
}
public void _$_clearFindViewByIdCache() {
if(this._$_findViewCache != null) {
this._$_findViewCache.clear();
}
}
}
Bytecode

Anko
● Anko is a library that uses Kotlin and provides a lot of extension functions to
make our Android development easier.
● It contains wrappers around the Android APIs and DSL that allows to us to
replace layouts written in the XML file

Anko
Gradle
dependencies {
// Anko
compile "org.jetbrains.anko:anko-sdk15:$anko_version"
compile "org.jetbrains.anko:anko-support-v4:$anko_version"
compile "org.jetbrains.anko:anko-appcompat-v7:$anko_version"
}

Anko - Layouts
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)
verticalLayout {
val name = editText()
button("Say Hello") {
onClick { toast("Hello, ${name.text}!") }
}
}

Anko - Layouts - Demo
class SignInActivity : AppCompatActivity() {
}
}
verticalLayout {
}
editText {
id = R.id.usernameEditText
hintResource = R.string.sign_in_username
textSize = 24f
}
editText {
id = R.id.passwordEditText
hintResource = R.string.signIn_password
textSize = 24f
}
button {
id = R.id.signIn_button
textResource = R.string.signIn_button
}
.lparams(width = matchParent, height = wrapContent)

}
}
verticalLayout {
}
editText {
textSize = 24f
}
editText {
textSize = 24f
}
button {
}
class SingInView : AnkoComponent<SignInActivity> {
override fun createView(ui: AnkoContext<SignInActivity>) = with(ui) {
}

}
}
class SingInView : AnkoComponent<SignInActivity> {
override fun createView(ui: AnkoContext<SignInActivity>) = with(ui) {
}
verticalLayout {
}
editText {
textSize = 24f
}
editText {
textSize = 24f
}
button {
}
SingInView().setContentView(this)

Anko - Buttons and Toasts
With Kotlin we can add click listener and show toast like this:
buttonNext.setOnClickListener {
Toast.makeText(baseContext, "CLicked!!", Toast.LENGTH_LONG).show;
}

Anko - Buttons and Toasts
With Kotlin we can add click listener and show toast like this:
but with Anko we can do it better:
buttonNext.setOnClickListener {
Toast.makeText(baseContext, "CLicked!!", Toast.LENGTH_LONG).show;
}
buttonNext {
onClick {
toast("Hello ${username.text}")
}
}
or we can show LONG toast:
onClick { longToast("Hello ${username.text}") }

Anko - Asynchronous Tasks
fun authorizeUser(username: String, password: String) {
doAsync {
val authorized = signInBL.checkUserCredentials(AuthCredentials(username = username, password = password))
activityUiThread {
if (authorized) toast("Signed!!!") else view.showAccessDeniedAlertDialog()
}
}
}

Since Anko 0.10-beta1 a new way Anko Coroutines
dependencies {
compile "org.jetbrains.anko:anko-coroutines:$anko_version"
}

Since Anko 0.10-beta1 a new way Anko Coroutines suspend fun getData(): Data { ... }
class MyActivity : Activity() {
fun loadAndShowData() {
// Ref<T> uses the WeakReference under the hood
val ref: Ref<MyActivity> = this.asReference()
async(UI) {
val data = getData()
// Use ref() instead of this@MyActivity
ref().showData()
}
}
fun showData(data: Data) { ... }
}

Since Anko 0.10-beta1 a new way Anko Coroutines fun getData(): Data { ... }
fun showData(data: Data) { ... }
async(UI) {
val data: Deferred<Data> = bg {
// Runs in background
getData()
}
// This code is executed on the UI thread
showData(data.await())
}
https://github.com/Kotlin/anko/wiki/Anko-Coroutines

Anko - Alerts
alert(message = "Hello, I'm Alert Dialog", title = "CZ KUG & eMan") {
yesButton { toast("YES pressed!") }
noButton { toast("NO pressed!") }
}.show()

Anko - Intents
Anko contains some useful wrappers for some common intents:
// Took it from original Anko documentation
// Make a call
makeCall(number) // Intent(Intent.ACTION_CALL, Uri.parse("tel:$number"))
// startActivity(intent)
// Send a text
sendSMS(number, [text])
//Browse the web
browse(url)
//Share some text
share(text, [subject])
//Send a email
email(email, [subject], [text])
Arguments in square brackets ([]) are optional

Anko - Intents
Start a new activity
val intent = Intent(this, SomeOtherActivity::class.java)
intent.putExtra("id", 5)
intent.setFlag(Intent.FLAG_ACTIVITY_SINGLE_TOP)
startActivity(intent)

Anko - Intents
Start a new activity
with Anko:
val intent = Intent(this, SomeOtherActivity::class.java)
intent.putExtra("id", 5)
intent.setFlag(Intent.FLAG_ACTIVITY_SINGLE_TOP)
startActivity(intent)
startActivity(intentFor<SomeOtherActivity>("id" to 5).singleTop())
startActivity<SomeOtherActivity>("id" to 5)

Anko - Logging
class SomeActivity : Activity(), AnkoLogger {
private fun someMethod() {
info("Prague is the capital of Czech Republic")
debug(5) // .toString() method will be executed
warn(null) // "null" will be printed
}
}
…..
info { "Prague is the capital of Czech Republic" }

Anko
● Anko SQLite
○ Provides lots of extension functions to simplify working with SQLite
dependencies {
compile
"org.jetbrains.anko:anko-sqlite:$anko_version"
}
class MySqliteOpenHelper : ManagedSQLiteOpenHelper {}
database.use {
// Here we have SQL
}

Anko
● Anko SQLite
val values = ContentValues()
values.put("id", 1)
values.put("name", "Vaclav")
values.put("email", "vaclav@email.com")
db.insert("User", null, values)
db.insert("User",
"id" to 1,
"name" to "Vaclav",
"email" to "vaclav@email.com"
)

Anko
● Anko SQLite
db.select("User", "name")
.whereArgs("(_id > {userId}) and (name = {userName})",
"userName" to "John",
"userId" to 42)
https://github.com/Kotlin/anko/wiki/Anko-SQLite

Modern SQL based query & persistance for Java / Kotlin / Android
https://github.com/requery/requery

Requery
● Object mapping and SQL generator for Java/Kotlin/Android
○ RxJava and Java 8 support
○ Create databases
○ Perform queries and updates

Requery
● Features
○ No Reflection
○ Typed query language
○ Table generation
○ Supports JDBC and most popular databases (MySQL, Oracle, SQL
Server, Postgres and more)

Requery
● Features
○ Compile time entity validation
○ Designed specifically with Android support in mind

Requery
● Using it
dependencies {
// Requery
compile "io.requery:requery:$requeryVersion"
compile "io.requery:requery-kotlin:$requeryVersion"
compile "io.requery:requery-android:$requeryVersion" // for android
}

Requery
● 1. Create Database Source
class MyDatabaseSource(context: Context, model: EntityModel, version: Int)
: DatabaseSource(context, model, version) {
override fun onCreate(db: SQLiteDatabase)
override fun onUpgrade(db: SQLiteDatabase?, oldVersion: Int, newVersion: Int)
}

Requery
● 2. Kotlin Entity Datastore
fun provideDataStore(databaseSource: FiboDatabaseSource): KotlinEntityDataStore<Persistable> {
...
}

Requery
if (BuildConfig.DEBUG) {
databaseSource.setTableCreationMode(TableCreationMode.DROP_CREATE)
}
...
}

Requery
}
val dataStore = KotlinEntityDataStore<Persistable>(databaseSource.configuration)
...
}

Requery
}
val dataStore = KotlinEntityDataStore<Persistable>(databaseSource.configuration)
databaseSource.dataStore = dataStore
return dataStore
}

Requery
● Entity
interface User : Persistable {
}

Requery
● Entity
@Entity
}

Requery
● Entity
@Entity
@Table
}

Requery
● Entity
@Entity
@Table(name = “USER”)
}

Requery
● Entity
@Entity
var id: Int
}

Requery
● Entity
@Entity
@get:Key
var id: Int
}

Requery
● Entity
@Entity
@get:Key
@get:Generated
var id: Int
}

Requery
● Entity
@Entity
@get:Key
@get:Generated
var id: Int
var userName: String
}

Requery
● Entity
@Entity
@get:Key
@get:Generated
var id: Int
@get:Column(length = 20, unique = true, nullable = false)
}

Requery
● Entity
@Entity
@get:Key
@get:Generated
var id: Int
@get:Column(length = 20, nullable = false)
var password: String
@get:Column(length = 20)
var firstName: String
var lastName: String
var email: String
}

Requery
● Entity
@Entity
@get:Key
@get:Generated
var id: Int
…
val userAccounts: List<UserAccount>
}

Requery
● Entity
@Entity
@get:Key
@get:Generated
var id: Int
...
@get:OneToMany
}

Requery
● Entity
@Entity
@get:Key
@get:Generated
var id: Int
@get:Column(length = 20, nullable = false)
var password: String
var firstName: String
var lastName: String
var email: String
@get:OneToMany
}

Requery
● Entity
@Entity
interface UserAccount : Parcelable, Persistable {
var user: User
var account: Account
}

Requery
● Entity
@Entity
interface UserAccount : Parcelable, Persistable {
@get:Key
@get:ForeignKey
@get:ManyToOne
var user: User
@get:ForeignKey
@get:ManyToOne
var account: Account
}

Requery
override fun existUser(): Boolean {
return dataStore.count(UserEntity::class).get().value() > 0
}

Requery
override fun findUserById(id: Int): UserDO? {
var userDO: UserDO? = null
dataStore.invoke {
val selectResult = select(UserEntity::class) where (UserEntity.ID.eq(id))
selectResult.get().firstOrNull()?.let { userDO = convertToDO(it) }
}
return userDO
}

Requery
override fun insertUser(credentials: AuthCredentials) {
val user = UserEntity()
with(user) {
userName = credentials.userName
password = credentials.password
}
dataStore.insert(user)
}

Requery
override fun insertUser(credentials: AuthCredentials) {
val user = UserEntity()
with(user) {
userName = credentials.userName
password = credentials.password
}
doAsync {
dataStore.insert(user)
}
}

Requery
● Transaction
dataStore {
withTransaction { }
}

KotlinPref
Android SharedPreferences delegation library for Kotlin
object UserInfoPrefModel : KotprefModel() {
var userId: Int by intPrefVar(default = -1)
var name: String by stringPrefVar()
}
Live Demo
https://github.com/chibatching/Kotpref

PaperParcel
Android Parcelable boilerplate annotation processor

PaperParcel
Parcelable
class UserDO protected constructor(ìn`: Parcel) : Parcelable {
private val id: Int
private val username: String
private val passoword: String
...
override fun writeToParcel(dest: Parcel, flags: Int) {
dest.writeInt(id)
dest.writeString(username)
dest.writeString(passoword)
}
companion object {
val CREATOR: Parcelable.Creator<UserDO> = object : Parcelable.Creator<UserDO> {
override fun createFromParcel(ìn`: Parcel): UserDO {
return UserDO(ìn`)
}
override fun newArray(size: Int): Array<UserDO?> {
return arrayOfNulls(size)
}
}
}
}

PaperParcel
@PaperParcel data class UserDO(var id: Int, var username: String, var password: String) : PaperParcelable {
companion object {
@JvmField val CREATOR = PaperParcelUserDO.CREATOR
}
}
https://github.com/grandstaish/paperparcel

Thanks your
for listening!
eman.cz

eMan Dev Meetup: Kotlin For Android (part 03/03) 18.5.2017

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eMan Dev Meetup: Kotlin For Android (part 03/03) 18.5.2017