krakdroid: scala on android

Scala Android

Konrad Malawski / @ktosoplGDG / PJUG / KSUG / SCKRK

KrakDroid 14.12.2012Sunday, December 16, 12

Sunday, December 16, 12

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/Sunday, December 16, 12

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

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!

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)

// ...}

You always have the type information at hand.

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

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

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("[]")

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

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

Oh! List<Thing>, sure!

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

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]

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 {

class ExampleActivity extends Activity with ImplicitContext with ScalaToasts

trait ScalaToasts {

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

trait ScalaToasts {

asToastable("Hello!").toast()

Collections

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

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

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

implicit val handler = new Handler

Simple Threading

inUiThread { // ...}

Simple Threading

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

Simple Threading

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

Implicit Conversion on Int

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

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

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

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_=(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...

Scala is addictive.

Let me warn you...

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!

KrakDroid 14.12.2012Sunday, December 16, 12

KrakDroid 14.12.2012

I love feedback! <3

krakdroid: scala on android

button button

photo button

scala issunday

scala issimplesunday

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oncreatebundle comments

comments newcomment

aircasting string

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