Android my Scala @ JFokus 2013

Scala Android

Konrad Malawski / @ktosopl
GeeCON / GDG / PJUG / KSUG / SCKRK
JFokus 06.02.2013
Wednesday, February 6, 13

Konrad Malawski
twitter: ktosopl


This will be...


This will Not be...


This will Not be...

a Java rant,
about app design.


This will be about...


This will be about...

shifting cognitive load
writing less code
fokus on goals, not means


Scala is


Scala is

Simple ,
but Hard.


Scala is Simple.


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,
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 RoboActivity
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
{
Guice is eager.
public static final String PHOTO_PATH Startup can take a few seconds!
= "picture_path";





// ...
}


Robo Guice
{

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



// ...
}


Stairway to Scala


Collections
(the gateway drug)


Collections


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;
}
}


public class Person {
private final String name;
private final String nick;
POJO
POSO*
*Actually just a Case Class
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) {
case class Person(name: String, nick: String)
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

val name: String



Case Classes

val person = Person("Bruce Wayne", "Manbat") // whoops!
val fixed = person.copy(nick = "Batman")
val self = Person(nick = "Ktoso" , name = "Konrad")

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

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

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


Scala Collections at Work
Given a list of People,
return all the Hero names.

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


Back to Android


Another look at the Java code
public class MakeANoteActivity extends RoboActivity

{





// ...
}


What if... Scala?
class class MakeANoteActivity ScalaActivity
publicMakeANoteActivity extendsextends RoboActivity
with
View.OnClickListener
with PhotoOperations with CalibrationOperations
{
val PhotoPath
public static final "picture_path"
= String PHOTO_PATH = "picture_path";
val PhotoAttached = String PHOTO_ATTACHED = "photo_attached";
public static final "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 username = findResource[String](R.string.my_username)
val friends = findResource[List[String]](R.string.friends)

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


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


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)


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


What if... Scala?
{
val PhotoPath = "picture_path"
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
lazy val save = findView(TR.save_button) Implicit Parameters


}


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


}


<TableLayout
android:id="@+id/login_table"

android:layout_gravity="center"

android:layout_height="wrap_content"

android:layout_width="wrap_content">

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

object TR {
val login_table = TypedResource[TableLayout](R.id.login_table)

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

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

}


<TableLayout
android:id="@+id/login_table"

android:layout_gravity="center"

android:layout_height="wrap_content"

android:layout_width="wrap_content">

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

object TR {
val login_table = TypedResource[TableLayout](R.id.login_table)

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

// ...
}


Types

You always have the type information at hand.

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


Menus


Menus = callbacks


Java

@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.game_menu, menu);
return true;
}

Menus = callbacks


Menus = callbacks Java

@Override
return true;
}

@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);
}
}



public class AnActivity extends Activity {

}

}



th is?
to ﬁx
ways
tyle
}
Ja v a-s public class AnActivity extends Activity {

}

Delegate! Delegate! Delegate! Java

public class GameMenu {
public boolean onCreateOptionsMenu(Menu menu) { /*...*/ }
public boolean onOptionsItemSelected(MenuItem item) { /*...*/ }
}

GameMenu gameMenu = ...

return gameMenu.onCreateOptionsMenu(menu);
}

return gameMenu.onOptionsItemSelected(item)
}

}


super class monster Java

public abstract class WithGameMenuActivity extends Activity {
public boolean onCreateOptionsMenu(Menu menu) { /*...*/ }
public boolean onOptionsItemSelected(MenuItem item) { /*...*/ }
}

public class AnActivity extends WithGameMenuActivity {

}




th is?
to ﬁx
ays
-styl ew
cala public class AnActivity extends Activity {
}
S

}

Converting is simple
@Override
override def onCreateOptionsMenu(Menu menu) =
val inflater = getMenuInflater()
menu)
return true;
true
}

@Override
override def onOptionsItemSelected(MenuItem item) =
item.getItemId() match {
switch (item.getItemId()) {
casecase R.id.new_game:
R.id.new_game => newGame(); true
case R.id.help
newGame(); => showHelp(); true
case _ return true; super.onOptionsItemSelected(item)
=>
} case R.id.help:
showHelp();
return true;
default:
return super.onOptionsItemSelected(item);
}
}


The Menu Trait Scala

trait GameMenu {

override def onCreateOptionsMenu(Menu menu) = {
inflater.inflate(R.menu.game_menu, menu)
true
} Uhm... but we're not an Activity here!
case R.id.new_game => newGame(); true
case R.id.help => showHelp(); true
case _ => super.onOptionsItemSelected(item)
}

}


The Menu Trait Scala

trait GameMenu {
Now we're sure "I'm in an Activity"
this: Activity =>

override def onCreateOptionsMenu(Menu menu) = {
inflater.inflate(R.menu.game_menu, menu)
true
}
case R.id.new_game => newGame(); true
case R.id.help => showHelp(); true
case _ => super.onOptionsItemSelected(item)
}

}


The Menu Traits

class MyGame extends Activity with GameMenu
with SomeContextMenu


An Implicit Context


Passing around Context

Toast.makeText(ctx, msg, LENGTH_LONG).show();

Intent intent = new Intent(context, LocalService.class);


An Implicit Context

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

Implicit != Explicit
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) {{
def toastMyName(name: String, ctx: Context)

} }



Implicit Parameters

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

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


Implicit Parameters

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

}

implicit val context: Context = getContext

toastMyName("Siegfried")

toastMyName("Siegfried")(context)


An Implicit Context
class ScalaActivity
extends Activity
with ImplicitContext

“I can be only mixed into
an Activity.”

trait ImplicitContext {
this: Activity =>

implicit val ctx = getContext
}

So I know this method!


Implicit Conversions


Implicit Context, remember?

toastMyName("Siegfried")

What if we could...

"Siegfried".toast()


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

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


}
Implicit Conversion: String => Toastable

trait ScalaToasts {

implicit def asToastable(str: String) =
new Toastable(str)
}
asToastable("Hello!").toast()


}
Implicit Conversion: String => Toastable

trait ScalaToasts {

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

class ExampleActivity
extends Activity
with ScalaToasts


}

trait ScalaToasts {

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

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


And there’s more!


Simple Threading

implicit val handler = new Handler

inUiThread {
// ...
}

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

Not a replacement for proper design


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

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


SharedPreferences

KanbaneryPreferences.projectId = 1337

val name: Option[Long] = KanbaneryPreferences.projectId


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()
}

withSharedPreferencesEditor {
_.putString(KeyLogin, number)
}


Let me warn you...

Scala is addictive.


Scala is addictive.


Scala my Android?


Scala my Android?

- Android Library projects?
- Not "Java level" IDE support?
- Debugging?
- ProGuard-ing time?
- Increased cognitive load?


Scala my Android?

+ No boilerplate
+ Focus on the app/domain
+ No need for reﬂection
+ Less cognitive load?
+ Scala libraries
+ SBT (build tool)


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.*
• Fully Open Source
• New version soon! Pull and play with it!
• Scaloid https://github.com/pocorall/scaloid
• Many of the things we've seen, a bit more; some awesome, some less

Mailing lists rock!


I love feedback! <3

Konrad Malawski / @ktosopl
GeeCON / GDG / PJUG / KSUG / SCKRK
JFokus 06.02.2013

Android my Scala @ JFokus 2013

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