KrakDroid: Scala on Android

Scala Android

Konrad Malawski / @ktosoplGDG / PJUG / KSUG / SCKRK

KrakDroid 14.12.2012Sunday, December 16, 12

http://blog.project13.pl

http://blog.project13.pl

http://twitter.com/ktosopl

http://twitter.com/ktosopl

http://krakow.gtug.pl

http://krakow.gtug.pl

http://java.pl

http://java.pl

http://sckrk.com

http://sckrk.com

http://krakdroid.pl

http://krakdroid.pl

Sunday, December 16, 12


Scala is


Scala is


Scala is


Scala is


Scala is

Simple


Scala is

Simple , but Hard.


Scala is Simple.


Scala is Simple.


Scala is Hard.

http://apocalisp.wordpress.com/2010/10/26/type-level-programming

-in-scala-part-7-natural-transformation%C2%A0literals/Sunday, December 16, 12

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/Sunday, December 16, 12







Scala is


Scala is

A Functional,


Scala is

A Functional,Object Oriented,


Scala is

A Functional,Object Oriented,Statically Typed,


Scala is


Scalable,


Scala is


Scalable,Language...


Scala is


Scalable,Language...

...running on the JVM and DVM!


Android


findViewByIdpublic 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); // ... }}





is null at first...





initialized in method...




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


Robo Guicepublic class MakeANoteActivity extends Activity 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;

// ... }

So many words...


Robo Guicepublic class MakeANoteActivity extends RoboActivity implements View.OnClickListener{ public static final String PHOTO_PATH = "picture_path"; public static final String PHOTO_ATTACHED = "photo_attached";





// ... }

Type changes in XML, but not here...

ClassCastException!


Robo Guicepublic class MakeANoteActivity extends RoboActivity implements View.OnClickListener{ public static final String PHOTO_PATH = "picture_path"; public static final String PHOTO_ATTACHED = "photo_attached";





// ... }

Guice is eager. Startup can take a few seconds!


Stairway to Scala


Another look at the Java codepublic class MakeANoteActivity extends RoboActivity implements View.OnClickListener

{ public static final String PHOTO_PATH = "picture_path"; public static final String PHOTO_ATTACHED = "photo_attached";





// ... }


public class MakeANoteActivity extends RoboActivity implements View.OnClickListener

{ public static final String PHOTO_PATH = "picture_path"; public static final String PHOTO_ATTACHED = "photo_attached";





// ... }

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?


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



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


public is default.







ScalaActivity gives us some magic methods








It’s so easy, YOU can implement it!








It’s so easy, YOU can implement it!







Instead of “...Helper”,use Traits.







Type Inference







Who’s missing here?







lazy initialization







Needs Context







What’s the type here?!?








Typed Resource - “a better R”









XML Type changes... Type here changes!




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: Button = findView(TR.share)





You can be explicit though!







What if... Scala?

Like @InjectResource, but smarter

Manifests vs. Type Erasure







Does String have a toast() method?

Implicit Conversion


Typed Resource


Typed Resource = Better R
















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) // ...

}








}







}

Wrappers







}







}


TR in Actionclass MakeANoteActivity extends ScalaActivity with View.OnClickListener with PhotoOperations with CalibrationOperations{ val PhotoPath = "picture_path" val PhotoAttached = "photo_attached"

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


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 ContextImplicit != Explicit

def toastMyName(name: String, ctx: Context) { import android.widget.Toast._ makeText(ctx, msg, LENGTH_LONG).show()}

toastMyName(”Siegfried”, getContext)





Explicit Parameter





Explicit ParameterExplicit Parameter





Import inside a method!






def toastMyName(name: String)(implicit ctx: Context) { import android.widget.Toast._ makeText(ctx, msg, LENGTH_LONG).show()}



Implicit ParametersImplicit != Explicit


Implicit Parameter







toastMyName("Siegfried")




implicit val context: Context = getContext





implicit val context: Context = getContext


toastMyName("Siegfried")(context)


An Implicit Context

class ScalaActivity extends Activity with ImplicitContext


An Implicit Context

trait ImplicitContext { this: Activity => implicit val ctx = getContext}



An Implicit Context



“I can be only mixed intoan Activity.”


An Implicit Context



“I can be only mixed intoan Activity.”

So I know this method!






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


Java




Java

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



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


Java






Java


Oh! List<Thing>, sure!




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


Java

Scala






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


Java

Scala



List[Thing]!


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








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) }


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



implicit





implicit Manifest





the type signature


Manifests vs. Type Erasuredef findResource[T](id: Int)(implicit ctx: Context, m: Manifest[T]): T = m.toString match { case "java.lang.String" => ctx.getString(id).asInstanceOf[T] case "java.util.ArrayList[java.lang.String]" => newArrayList(ctx.getString(id).asInstanceOf[T])



see the type... at runtime



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





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



java.lang.String has this...?


Implicit Conversions



Implicit != Explicit


Implicit ConversionsImplicit != Explicit









Implicit Context, remember?




What if we could...




"Siegfried".toast()

What if we could...





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




Decorator




DecoratorConstructor




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







trait ScalaToasts {

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




trait ScalaToasts {


Implicit Conversion: String => Toastable




trait ScalaToasts {


asToastable("Hello!").toast()





trait ScalaToasts {






trait ScalaToasts {


class ExampleActivity extends Activity with ImplicitContext with ScalaToasts




trait ScalaToasts {






trait ScalaToasts {

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





trait ScalaToasts {






trait ScalaToasts {






trait ScalaToasts {






trait ScalaToasts {



asToastable("Hello!").toast()




Collections


POJO


POJOpublic class Person { private final String name; private final String nick;

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; }}


POJOpublic class Person { private final String name; private final String nick;

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)



val name: String

POSO**Actually just a Case Class



Case Classes



Case Classes



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

Case Classes




Case Classes

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




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

Case Classes






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

Case Classes






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

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

Case Classes

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 BestGiven a list of People,

return all the Hero names.


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 bestGiven a list of People,



Java + Guava at their best

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

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



Scala Collections at WorkGiven a list of People,



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

Scala Collections at WorkGiven a list of People,



And there’s more!


Simple Threading


Simple Threading

implicit val handler = new Handler


Simple Threading


inUiThread { // ...}


Simple Threading


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



Simple Threading


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


Implicit Conversion on Int


on___

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

Java


on___

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

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

Java

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!


SharedPreferencesobject KanbaneryPreferences {

private val KeyLogin = "login"

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

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





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





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

}





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



block(editor)

editor.commit()}


SharedPreferences



block(editor)

editor.commit()}


SharedPreferences



block(editor)

editor.commit()}

withSharedPreferencesEditor { _.putString(KeyLogin, number) }


String interpolation(scala 2.10)







Won’t compile!


Let me warn you...


Let me warn you...

Scala is addictive.


Let me warn you...

Scala is addictive.


Scala is addictive.


Scala is addictive.


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!


http://www.scala-lang.org/


http://www.scalakoans.org/


http://www.blog.project13.pl


https://github.com/jberkel/android-plugin


https://github.com/ktoso/kanbanery-tv


https://github.com/pocorall/scaloid


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!















KrakDroid 14.12.2012Sunday, December 16, 12


KrakDroid 14.12.2012

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Technology

KrakDroid: Scala on Android