Developing
Android apps
with Kotlin
AVGeeks, June 2016
Shem Magnezi

Shem Magnezi
@shemag8 | shem8.github.com

Java is great
▣ Very popular.
▣ Great community.
▣ Lots of frameworks and libraries.
▣ Supported by big companies (Oracle &
Google).
▣ Portable, fast, well documented.
▣ Great IDEs
▣ You can write server side, web and mobile.

Yes but...
▣ Lot’s of boilerplate
▣ Null checks
▣ Exception handling
▣ Function pointers
▣ Data classes (POJO)
▣ Extension functions
▣ Operator overloading
▣ String interpolation
▣ And more...

On Android it even worse
▣ Barely support Java 8 (N+)
▣ Partially support Java 7 (KitKat+)
▣ There are some libraries that fill some of the
missing features (retro lambda, RX, etc..) but
it’s not the same.
▣ It mainly feel too ‘heavy’ for front end code.

Kotlin
Statically typed programming language
for the JVM, Android and the browser
100% interoperable with Java™

Kotlin?
▣ Open source, lead by JetBrains.
▣ JVM language (Like Scala, Groovy and Clojure)
▣ Can call Java code and vice versa.
▣ Fully integrated IDE.
▣ Small (600KB before ProGuard).
▣ Statically typed so no runtime overhead.
▣ Used by a lot of big companies, even by the
Android team (data binding).

Code!

1.
Basic syntax

when (x) {
in 1..10 -> print("x is in the range")
in validNumbers -> print("x is valid")
!in 10..20 -> print("x is outside the range")
else -> print("none of the above")
}
fun mul(x: Int, y: Int = 2): Int {
return x * y
}
fun mul(x: Int, y: Int = 2) = x * y
view.setOnClickListener({ //click handling })

if (obj is String) {
print(obj.length)
}
val items = listOf(1, 2, 3, 4)
items.first() == 1
items.last() == 4
items.filter { it % 2 == 0 } // returns [2, 4]
ints.forEach {
if (it == 0) return
print(it)
}

2.
Null Safety

‘’
I call it my billion-dollar mistake. It
was the invention of the null
reference in 1965 ... My goal was to
ensure that all use of references
should be absolutely safe... This has
led to innumerable errors,
vulnerabilities, and system crashes,
which have probably caused a
billion dollars of pain and damage in
the last forty years.
Tony Hoare

var a: String = "abc"
a = null // compilation error
var b: String? = "abc"
b = null // ok
val l = b?.length ?: -1

3.
Data Classes

data class User(val name: String, val age: Int)
You get for free:
▣ equals()
▣ hashCode()
▣ toString() of the form "User(name=John, age=42)",
▣ copy() function
▣ getters()

4.
Extensions
Functions

fun Date.isThuesday() Boolean {
return day == 2
}
if (date.isTuesday) {
...
}
fun Date.isThuesday() = day == 2

fun SQLiteDatabase.inTransaction(func: () -> Unit) {
beginTransaction()
try {
func()
setTransactionSuccessful()
} finally {
endTransaction()
}
}
db.inTransaction {
}

fun AppCompatActivity.navigate(frag: Fragment) {
val fragmentTransaction = supportFragmentManager.beginTransaction()
fragmentTransaction.replace(content.id, frag);
fragmentTransaction.commit();
}
fun Fragment.userError(msg: String?) {
Snackbar.make(view, msg, Snackbar.LENGTH_LONG).show()
}

fun SharedPreferences.edit(func:SharedPreferences.Editor.(): Unit) {
val editor = edit()
editor.func()
editor.apply()
}
fun SharedPreferences.Editor.set(pair: Pair<String, String>) = putString(pair.first, pair.second)
preferences.edit {
set("foo" to "bar")
set("fizz" to "buzz")
remove("username")
}

inline fun <T: View> T.afterMeasured(crossinline f: T.() -> Unit) {
viewTreeObserver.addOnGlobalLayoutListener(object : ViewTreeObserver.OnGlobalLayoutListener {
override fun onGlobalLayout() {
if (measuredWidth > 0 && measuredHeight > 0) {
viewTreeObserver.removeOnGlobalLayoutListener(this)
f()
}
}
})
}
recycler.afterMeasured {
val columnCount = width / columnWidth
layoutManager = GridLayoutManager(context, columnCount)
}

5.
Android
Extensions

// Using R.layout.activity_main from the main source set
import kotlinx.android.synthetic.main.activity_main.*
public class MyActivity : Activity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
textView.setText("Hello, world!") // Instead of findView(R.id.textView) as TextView
}
}

6.
Anko library

override 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
}
}
}

There is much more:
▣ kotlinlang.org
▣ blog.jetbrains.com/kotlin
▣ kotlinlang.org/docs/resources.html
▣ Kara- An MVC Framework
▣ Android Kotlin Extensions- A collection of Android Kotlin
extensions
▣ KAndroid- Kotlin library for Android
▣ Anko- Pleasant Android application development

Thanks!
Any questions?
You can find this presentation at: shem8.github.io
smagnezi8@gmail.com
Presentation template by SlidesCarnival | Photographs by Unsplash

Credits
Android Development with Kotlin - Jake Wharton
Droidcon SF - Better Android Development with Kotlin and
Gradle
Special thanks to all the people who made and released these
awesome resources for free:
▣ Presentation template by SlidesCarnival
▣ Photographs by Unsplash