KrakDroid: Scala on Android

Scala Android

Konrad Malawski / @ktosopl
GDG / PJUG / KSUG / SCKRK
KrakDroid 14.12.2012
Sunday, December 16, 12

Scala is


Scala is

Simple


Scala is

Simple ,
but Hard.


Scala is Simple.


Scala is Hard.

http://apocalisp.wordpress.com/2010/10/26/
type-level-programming
-in-scala-part-7-natural-transformation%C2%A0literals/

Scala is Hard.
object
Param
{

implicit
def
pToT[A[_],
B[_]](f:
(p:
Param[A])
=>
B[p.T]):
A~>B
=
new
(A
~>
B)
{

def
apply[s](a:
A[s]):
B[s]
=
{

val
v:
Param[A]
{
type
T
=
s}
=
new
Param[A]
{

type
T
=
s

def
in
=
a

}

f(v)

}

}

}

http://apocalisp.wordpress.com/2010/10/26/
type-level-programming
-in-scala-part-7-natural-transformation%C2%A0literals/

Scala is
A Functional,


Scala is
A Functional,
Object Oriented,


Scala is
A Functional,
Object Oriented,
Statically Typed,


Scala is
A Functional,
Object Oriented,
Statically Typed,
Scalable,


Scala is
A Functional,
Object Oriented,
Statically Typed,
Scalable,
Language...


Scala is
A Functional,
Object Oriented,
Statically Typed,
Scalable,
Language...

...running on the JVM and DVM!


Android


ﬁndViewById
public class MyActivity extends Activity {

ListView comments;
Button newComment;

@Override
void onCreate(Bundle bundle) {
super.onCreate(bundle);
comments = (ListView) findViewById(R.id.comments);
newComment = (Button) findViewById(R.id.new_comment);
// ...
}
}


ﬁndViewById

ListView comments;
is null at ﬁrst...
Button newComment;

@Override
// ...
}
}


ﬁndViewById

ListView comments;
Button newComment;
initialized in
@Override method...
// ...
}
}


ﬁndViewById

ListView comments;
Button newComment;

@Override
// ...
}
}
Explicit casting!


Robo Guice
So many
public class MakeANoteActivity
extends Activity
words...
implements View.OnClickListener
{
public static final String PHOTO_PATH = "picture_path";
public static final String PHOTO_ATTACHED = "photo_attached";

@Inject SessionManager sessionManager;
@Inject LocationHelper locationHelper;
@Inject PhotoHelper photoHelper;
@Inject Application context;

@Inject CalibrationHelper calibrationHelper;

@InjectView(R.id.attach_photo) Button attachPhoto;
@InjectView(R.id.note_text) EditText noteText;
@InjectView(R.id.save_button) Button save;
@InjectView(R.id.date) TextView dateText;
@InjectView(R.id.share) Button share;

@InjectResource(R.string.im_aircasting) String imAircasting;
@InjectResource(R.string.share_with) String shareWith;

// ...
}


Robo Guice
extends RoboActivity
{

@Inject LocationHelper locationHelper; Type changes in XML,
@Inject PhotoHelper photoHelper; but not here...
ClassCastException!



// ...
}


Robo Guice
extends RoboActivity
{

@Inject LocationHelper locationHelper; Guice is eager.
@Inject PhotoHelper photoHelper; Startup can take a few seconds!




// ...
}


Stairway to Scala


Another look at the Java code
public class MakeANoteActivity extends RoboActivity

{





// ...
}


What if... Scala?
public class MakeANoteActivity extends RoboActivity

{





// ...
}


What if... Scala?
class MakeANoteActivity extends ScalaActivity
with View.OnClickListener
with PhotoOperations with CalibrationOperations
{
val PhotoPath = "picture_path"
val PhotoAttached = "photo_attached"

lazy val sessionManager = SessionManager.get
lazy val locationManager = LocationManager.get

lazy val attachPhoto = findView(TR.attach_photo)
lazy val noteText = findView(TR.note_text)
lazy val save = findView(TR.save_button)
lazy val dateText = findView(TR.date)
lazy val share = findView(TR.share)

val imAircasting = findResource[String](R.string.im_aircasting)
val shareWith = findResource[String](R.string.share_with)

def toastConferenceName() = "KrakDroid".toast()
}


What if... Scala?
{
public is default. = "picture_path"
val PhotoPath



val username = findResource[String](R.string.my_username)
val friends = findResource[List[String]](R.string.friends)

}


What if... Scala?
{
ScalaActivity gives us some
magic methods



}


What if... Scala?
It’s so easy,
with View.OnClickListener YOU can implement it!
{
ScalaActivity gives us some
magic methods



}


What if... Scala?
Instead of “...Helper”,
{ use Traits.




}


What if... Scala?
{
Type Inference




}


What if... Scala?
{


Who’s missing here?



}


What if... Scala?
{


lazy initialization


}


What if... Scala?
{


Needs Context


}


What if... Scala?
{

What’s the type here?!?



}


What if... Scala?
{

Typed Resource - “a better R”



}


What if... Scala?
{



XML Type changes... Type here changes!

}


What if... Scala?
{


lazy val share: Button = findView(TR.share)

You can be explicit though!

}


What if... Scala?
{


lazy val share = Like @InjectResource, but
findView(TR.share) smarter


}
Manifests vs. Type Erasure


What if... Scala?
{



Does String have a toast()
val username = findResource[String](R.string.my_username) method?

}

Implicit Conversion


Typed Resource


Typed Resource = Better R


{




}


{


lazy val share = findView(TR.share) Typed Resource


}



case class TypedResource[T](id: Int)
case class TypedLayout(id: Int)

object TR {
val columns_pager = TypedResource[ViewPager](R.id.columns_pager)

val workspaces = TypedResource[ExpandableListView](R.id.workspaces)

val subtask_txt = TypedResource[TextView](R.id.subtask_txt)
// ...

}



case class TypedResource[T](id: Int)
case class TypedLayout(id: Int) Wrappers

object TR {
val columns_pager = TypedResource[ViewPager](R.id.columns_pager)

val workspaces = TypedResource[ExpandableListView](R.id.workspaces)

val subtask_txt = TypedResource[TextView](R.id.subtask_txt)
// ...

}


TR in Action
{

lazy val sessionManager = SessionManager.get // magic here but
lazy val locationManager = LocationManager.get // we’ll see this later!


// magic here too, but we’ll implement this in a few slides!
val imAircasting = findResource[String](R.string.im_aircasting)

// ...
}


Types


Types

You always have the type information at hand.


Types

You always have the type information at hand.

(IntelliJ IDEA, Ensmine/Emacs, Eclipse)
⌘ SHIFT I
ALT =


An Implicit Context


An Implicit Context

Implicit != Explicit


An Implicit Context

def toastMyName(name: String, ctx: Context) {
import android.widget.Toast._

makeText(ctx, msg, LENGTH_LONG).show()
}

toastMyName(”Siegfried”, getContext)


An Implicit Context


}
Explicit Parameter



An Implicit Context
Import inside a method!


}



An Implicit Context

def toastMyName(name: String)(implicit ctx: Context) {

}


Implicit Parameters


makeText(ctx, msg, LENGTH_LONG).show() Implicit Parameter
}


Implicit Parameters


}


Implicit Parameters


}

toastMyName("Siegfried")


Implicit Parameters


}

implicit val context: Context = getContext



Implicit Parameters


}

implicit val context: Context = getContext


toastMyName("Siegfried")(context)


An Implicit Context
class ScalaActivity
extends Activity
with ImplicitContext


An Implicit Context
class ScalaActivity
extends Activity

trait ImplicitContext {
this: Activity =>

implicit val ctx = getContext
}


An Implicit Context
class ScalaActivity
extends Activity

“I can be only mixed into
an Activity.”

this: Activity =>

}


An Implicit Context
class ScalaActivity
extends Activity

“I can be only mixed into
an Activity.”

this: Activity =>

}

So I know this method!



List<Thing> t = marshaller.parseList("[]")

Java


Uhm... List<Object>...?


Java




Java
List<Thing> t = marshaller.parseList("[]", Thing.class)




Java Oh! List<Thing>, sure!







Scala val t: List[Thing] = marshaller.parseList("[]")






Scala val t: List[Thing] = marshaller.parseList("[]")

List[Thing]!


def findResource[T](id: Int)(implicit ctx: Context, m: Manifest[T]): T =
m.toString match {
case "java.lang.String" =>
ctx.getString(id).asInstanceOf[T]

case other =>
throw new UnableToResolveResource(ofType = other, id = id)
}



m.toString match {
ctx.getString(id).asInstanceOf[T] implicit

case other =>
}



m.toString match {
ctx.getString(id).asInstanceOf[T] implicit Manifest

case other =>
}



m.toString match {
ctx.getString(id).asInstanceOf[T] the type signature

case other =>
}



m.toString match {
ctx.getString(id).asInstanceOf[T] see the type... at runtime

case "java.util.ArrayList[java.lang.String]" =>
newArrayList(ctx.getString(id).asInstanceOf[T])

case other =>
}



m.toString match {


case "Int" =>
ctx.getString(id).toInt.asInstanceOf[T]

case other =>
}



m.toString match {


case "Int" =>
ctx.getString(id).toInt.asInstanceOf[T]

case other => java.lang.String has this...?
}



Implicit Conversions


Implicit Context, remember?





What if we could...




What if we could...

"Siegfried".toast()


class Toastable(msg: String) {
def toast()(implicit ctx: Context) = ???
}


Decorator

}


Decorator
Constructor
}


}

new Toastable("Hello!").toast()


}

trait ScalaToasts {

implicit def asToastable(str: String) =
new Toastable(str)
}


}
Implicit Conversion: String => Toastable

trait ScalaToasts {

new Toastable(str)
}


}
Implicit Conversion: String => Toastable

trait ScalaToasts {

new Toastable(str)
}
asToastable("Hello!").toast()


}

trait ScalaToasts {

new Toastable(str)
}

class ExampleActivity
extends Activity
with ScalaToasts


}

trait ScalaToasts {

new Toastable(str)
} "Hello!".toast()

extends Activity
with ScalaToasts


}

trait ScalaToasts {

new Toastable(str)
} "Hello!".toast()

extends Activity asToastable("Hello!").toast()
with ScalaToasts


Collections


POJO


public class Person {
private final String name;
private final String nick;
POJO
public Person(String name, String nick) {
this.name = name;
this.nick = nick;
}

public String getName() {
return name;
}

public String getNick() {
return nick;
}

@Override
public boolean equals(Object o) {
if (this == o) return true;
if (!(o instanceof Person)) return false;

Person person = (Person) o;

if (name != null ? !name.equals(person.name) : person.name != null) return false;
if (nick != null ? !nick.equals(person.nick) : person.nick != null) return false;

return true;
}

@Override
public int hashCode() {
int result = name != null ? name.hashCode() : 0;
result = 31 * result + (surname != null ? surname.hashCode() : 0);
return result;
}
}


POSO*
*Actually just a Case Class

case class Person(name: String, nick: String)


POSO*
*Actually just a Case Class

val name: String



Case Classes



Case Classes

val person = Person("Bruce Wayne", "Manbat") // whoops!


Case Classes

val fixed = person.copy(nick = "Batman")


Case Classes


val self = Person(nick = "Ktoso" , name = "Konrad")


Case Classes



val Person(name, hero) = person
val hello = ”Hello” + name + ” ” + surname


Case Classes



val Person(name, hero) = person
val hello = ”Hello” + name + ” ” + surname

fixed.toString should equal (”Person(Bruce Wayne, Batman)”)

Still thinking assertThat().isEqualTo() is clean?


Given a list of People,
return all the Hero names.



public List<String> heroNames(List<Person> allPersons) {
List<String> donePersons =
new ArrayList<String>(allPersons.size());

for (Person person : allPersons) {
if (person.isHero()) {
donePersons.add(person.getName());
}
}

return ImmutableList.copyOf(donePersons);
}


Java with Guava at their Best


Java with Guava at their Best
return FluentIterable
.from(people)
.filter(new Predicate<Person>() {
@Override
public boolean apply(Person person) {
return person != null && person.isHero();
}
})
.transform(new Function<Person, String>() {
@Override
public String apply(Person input) {
return input.getName();
}
})
.toImmutableList();


Java + Guava at their best


Java + Guava at their best

return FluentIterable
.from(people)
.filter(isSuperHero)
.transform(heroToName)
.toImmutableList();

Java, yet pretty slick :-)
I <3 Guava.


Scala Collections at Work


Scala Collections at Work

def heroNames(people: List[Person]) =
people filter(_.isHero) map { _.name}


And there’s more!


Simple Threading


Simple Threading

implicit val handler = new Handler


Simple Threading


inUiThread {
// ...
}


Simple Threading


inUiThread {
// ...
}

inFutureWithProgressDialog(timeout = 10.seconds) {
// ...
}


Simple Threading


inUiThread {
// ...
}

inFutureWithProgressDialog(timeout = 10.seconds) {
// ...
} Implicit Conversion on Int


on___
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Java // ...
}
});


on___
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Java // ...
}
});

button onClick { view =>
Scala // ...
}


SharedPreferences


SharedPreferences

KanbaneryPreferences.projectId = projectId


SharedPreferences


val name: Option[Long] = KanbaneryPreferences.projectId


SharedPreferences


val name: Option[Long] = KanbaneryPreferences.projectId

What? No implicits?! Assume it works! Skip!


SharedPreferences
object KanbaneryPreferences {

private val KeyLogin = "login"

private def sharedPreferences(implicit ctx: Context) = ???

def login(implicit ctx: Context) =
sharedPreferences.getString(KeyLogin, "")


SharedPreferences
object KanbaneryPreferences {

private val KeyLogin = "login"

private def sharedPreferences(implicit ctx: Context) = ???

def login_=(number: String)(implicit ctx: Context) {
withSharedPreferencesEditor {
_.putString(KeyLogin, number)
}

}


SharedPreferences

def withSharedPreferencesEditor
(block: SharedPreferences.Editor => Unit)
(implicit ctx: Context) {

val editor = sharedPreferences.edit()

block(editor)

editor.commit()
}


SharedPreferences

def withSharedPreferencesEditor
(block: SharedPreferences.Editor => Unit)
(implicit ctx: Context) {

val editor = sharedPreferences.edit()

block(editor)

editor.commit()
}

withSharedPreferencesEditor {
_.putString(KeyLogin, number)
}


String interpolation
(scala 2.10)


String interpolation
(scala 2.10)

Won’t compile!


Let me warn you...


Let me warn you...

Scala is addictive.


Scala is addictive.


def links =
• Scala Lang http://www.scala-lang.org/
• Scala Koans http://www.scalakoans.org
• Blog.Project13.pl - http://www.blog.project13.pl
• SBT Android Plugin - https://github.com/jberkel/android-plugin
• Kanbanery for Android - https://github.com/ktoso/kanbanery-tv
• Check pl.project13.scala.android.*
• Now OpenSource, in Scala, and Lunar Logic is helping to dev :-)
• New version soon! Pull and play with it!
• Scaloid https://github.com/pocorall/scaloid
• Though I don’t think their impl. is very clean some things are v. nice!


def links =
• Scala Lang http://www.scala-lang.org/
• Scala Koans http://www.scalakoans.org
• Blog.Project13.pl - http://www.blog.project13.pl
• SBT Android Plugin - https://github.com/jberkel/android-plugin
• Kanbanery for Android - https://github.com/ktoso/kanbanery-tv
• Check pl.project13.scala.android.*
• Now OpenSource, in Scala, and Lunar Logic is helping to dev :-)
• New version soon! Pull and play with it!
• Scaloid https://github.com/pocorall/scaloid
• Though I don’t think their impl. is very clean some things are v. nice!

Mailing lists rock!


Konrad Malawski / @ktosopl

I love feedback! <3 Konrad Malawski / @ktosopl

KrakDroid: Scala on Android

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