Android is a fast-growing mobile operating system with millions of users worldwide. Scala is a modern programming language designed to express common programming patterns in a concise, elegant, and type-safe way. Why not combine both of them?

1. Scaladroids
Ostap Andrusiv

2. About me

3. Agenda
What is android? What is scala?
Scala your android?

4. Why Scala?Why Scala?

5. Scala
Concise
Type-safe
Functional && OO

6. RSSReader
~400
~150
LOC

7. Expressions & Values
pif@pif:~/ $ scala
scala> 20 + 22
res1: Int = 42
scala> val fourtyTwo = 100 - 58
fourtyTwo: Int = 42
scala> fourtyTwo = -1
<console>:8: error: reassignment to val
scala> var number = 42
number: Int = 42
scala> number = -1
number: Int = -1

8. Functions
pif@pif:~/ $ scala
scala> def add42(a: Int) =
| a + 42
add42: (a: Int)Int
scala> add42(50 + 5*5*2)
res0: Int = 142
scala> def minusOne() =
| -1
minusOne: ()Int
scala> 43 + minusOne
res1: Int = 42

9. Java Class
public class RSSEntry {
private String name;
private String description;
private String link;
public RSSEntry(String name, String description, String link) {
super();
this.name = name;
this.description = description;
this.link = link;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
// ... 50 LINES more !!!

10. 1

11. Scala class
class RSSEntry(name: String, description: String, link: String) {
// that's it! Nothing more!
case class RSSEntry(name: String, description: String, link: Stri
// class + equals(), hashCode() & lots of other useful stuff
object RSSEntry {
def customize() = ...
}

12. Basic Inheritance & Traits
class RSSEntry(name: String, desc: String) {}
// that's it! Nothing more!
class AuthoredRSSEntry(name: String, desc: String, author: String
extends RSSEntry(name, desc
trait HtlmView {
def asHTLMString() : String
}
trait PlainView {
def asPlainText() : String
}
class NiceRSSEntry(name: String, desc: String)
extends RSSEntry(name, desc
with HtmlView
with PlainView {
// ... asHTLMString & asPlainText

13. Collections FTW!
Task: From all #ADD tweets,
find those programmers,
who know .NET and give them Coockies!!!
Java: // ~50 lines of mess and pain in the ass...
Scala:
tweets
.filter (_ contains "#ADD13")
.flatMap(_ split " " )
.filter (_ startsWith "@" )
.map (t => person(t))
.filter (_ langs contains (".net"))
.foreach(giveCookies _)
//import scala.collection.JavaConverters._

14. Scaladroiding...
* -- S for Scala

15. Layout
<LinearLayout xmlns:android="http://schemas.android.com/ap...
android:layout_width... >
<TextView android:id="@+id/text_name"
android:textSize... />
<TextView android:id="@+id/text_descr"
android:textSize... />
</LinearLayout>
// ... in R.java:
public final class R {
// ...
public static final class id {
// ...
public static final int text_descr=0x7f090003;
public static final int text_name=0x7f090002;
}

16. Layout Usage
// ... in Java:
TextView itemName = (TextView) findViewById(R.id.text_name);
TextView itemDesc = (TextView) findViewById(R.id.text_descr);
itemName.setText(item.getShortName());
itemDesc.setText(item.getShortDescription());
// ... in Scala:
val itemName = findViewById(R.id.text_name).asInstanceOf[TextView
val itemDesc = findViewById(R.id.text_descr).asInstanceOf[TextVie
itemName.setText(item.getShortName)
itemDesc.setText(item.getShortDescription)

17. TypedResource TR.scala
object TR {
val itemName = TypedResource[android.widget.Button](R.id.text_n
// ...
}
// ==> ... in Scala:
val itemName = findViewById(R.id.text_name).asInstanceOf[TextView
val itemDesc = findViewById(R.id.text_descr).asInstanceOf[TextVie
val itemName = findView(TR.itemName)
val itemDesc = findView(TR.itemDesc)

18. Event Handlers & Listeners
// ... in Java:
Button b = (Button) findViewById(R.id.action_check);
b.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// ... make user happy :)
}
});
// ... in Scala:
val b = findView(TR.buttonCheck)
b setOnClickListener(new View.OnClickListener {
override def onClick(v: View) {
// ... make user happy :)
}
})
// hmmm... no benefit from this :( ?

19. Event Handlers & Listeners
// ... in Scala:
val b = findView(TR.buttonCheck)
b setOnClickListener(new View.OnClickListener {
override def onClick(v: View) {
// ... make user happy :)
}
})
// hmmm... no benefit from this :( ?
// this is java-like scala! Rewrite it:
b onClick { /* make user happy */ }
// b has no onClick method!!! Where is it from?

20. Implicits
// ... in Scala:
class ShortString(s: String) {
def short =
if (s.length > 10)
s.substring(0,7) + “...”
else
s
}
new ShortString(“Very very long greeting”).short
// Very ve...
implicit def string2Shortstr(s: String) = new ShortString(s)
“Very very long greeting”.short
// Very ve...

21. "Pimp My Library" Ninja!

22. Implicits
// ... in Scala:
class ClickableView(v: View) {
def onClick(u: Unit) {
v.setOnClickListener(new View.OnClickListener() {
override def onClick(v: View) = u
})
}
}
implicit def view2ClickView(v: View) = new ClickableView(v)
// ... later in Scala:
b onClick { “make user happy”.toast }
// oh... implicit ..toasts?

23. Implicits
// ... in Java:
Toast.makeText(ctx, "Toast!", Toast.LENGTH_LONG).show();
// ... in Scala:
class ToastableString(s: String) {
def toast(ctx: Context) =
Toast.makeText(ctx, s, Toast.LENGTH_LONG).show
}
// ... later in Scala:
“make user happy”.toast(getApplicationContext)
// find 1 difference:
“make user happy”.toast
// wtf? Where can we get context?

24. // ... magic is in Scala:
trait Toasty {
class ToastString(s: String) {
def toast(implicit ctx: Context) =
Toast.makeText(ctx, s, Toast.LENGTH_LONG).show
}
implicit def string2ToastString(s: String) = new ToastString(s)
}
class NiceActivity extends Activity with Toasty {
implicit val ctx = getApplicationContext
“make users happy”.toast
}
Implicits

25. Shared Preferences
// ... in Java:
SharedPreferences.Editor sp = ctx.getSharedPreferences(KEY, 0).ed
editor.putString("hello", "world");
editor.commit();
// ... in Scala:
AppSharedPrefs.hello = "Julia"
(AppSharedPrefs.hello + ", you look awesome!").toast

26. Menus
// ... in Java:
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.entries, menu);
return true;
}
// ... in Scala:
trait Menus {
override def onCreateOptionsMenu(menu: Menu) = {
getMenuInflater.inflate(R.menu.entries, menu)
true
}
}
class EntriesActivity extends ListActivity with Menus

27. Closable
// ... in Java:
try {
// do some tricky work...
finally {
tricky.close();
}
// ... in Scala:
trait Closers {
def closeAfter[A <: {def close():Unit}, B](param:A)(f: A => B):
try { f(param) } finally { param.close }
}
}
// work with DB cursors:
closeAfter(db.query(...params...)) {
cu =>
// analyze cursor data
}

28. Async Tasks
// ... in Javish Scala:
new AsyncTask[String, Void, Object] {
override def doInBackground(params: String*) : Object = {
// download data
}
}.execute()

29. Async Tasks
// ... in Scala:
async {
// download data
}
// same applies to Handlers, post, threads, etc.

30. Scala Issues on Android
Maps API
wrapper or
v2 API
Solutions:
ProGuard

31. Magic behind

32. Magic behind

34. Let the Scala be with you!
? *Thanks!
Coursera
Twitter Scala School
Twitter Effective Scala
Odersky Book
stackoverflow