Scala and Android

Gotchas

• Android -> kind of Java 7 -> Scala 2.11.8 max
• virtually requires proguard and/or multidex
• proguard 5.1 doesn't "like" Scala versions prior to 2.11.5

Gradle - less invasive approach

Gradle

• IntelliJ support for WYSIWYG
• all normal tutorials and docs could be easily applied
• no Scala formatters, coverage etc

gradle-android-scala-plugin

buildscript {
  dependencies {
      classpath "com.android.tools.build:gradle:1.3.1"
      classpath "jp.leafytree.gradle:gradle-android-scala-plugin:1.4"
  }
}

apply plugin: "com.android.application"
apply plugin: "jp.leafytree.android-scala"

dependencies {
  compile "org.scala-lang:scala-library:2.11.7"
}

gradle-android-scala-plugin

• existed since 2014
• supports Scala 2.10.5 and 2.11.7
• no support for Scala compiler plugins
• requires manual config of multidex and/or proguard
• last update 5 months ago

SBT - complete Scala experience

sbt-android

addSbtPlugin("org.scala-android" % "sbt-android" % "1.6.15")

androidBuild
platformTarget := "android-21"

sbt-android

• existed since 2012
• allows to use any Scala version (though 2.11.5 min would be best)
• requires manual config of multidex and/or proguard
• last update few days ago

sbt-android-gradle

• imports all settings from Gradle project into SBT
• we could maintaining project in Gradle and then reflect changes to SBT
• we can migrate Gradle to SBT and then remove Gradle build
• changes made manually would not be maintained so we would have to reapply

Different flavors of UI development

Ol' good XML/Java

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="wrap_content" android:padding="20dip">
  <TextView android:layout_width="match_parent" android:text="ID"
      android:id="@+id/userid" android:layout_height="wrap_content" />
  <EditText android:layout_width="match_parent"
      android:layout_height="wrap_content" android:id="@+id/userId" />
  <Button android:layout_width="match_parent"
      android:layout_height="wrap_content" android:id="@+id/signin"
      android:text="Sign in"/>
</LinearLayout>

Ol' good XML/Java

EditText userId = (EditText)findByViewId(R.id.userid);
Button signin = (Button)findByViewId(R.id.signin);
signin.setOnClickListener(new View.OnClickListener() {
  public void onClick(View v) {
    signin(userId.getText());
  }
});

Ol' good XML/Java

• all tools support them
• documentation is using them, so no need to translating concepts into sth else
• verbose

Scaloid

new SVerticalLayout {
    STextView("ID")
    val userId = SEditText()
    SButton("Sign in", signin(userId.text))
  }.padding(20 dip)

Scaloid

• less verbosity
• uses Scala features to create DSL
• has online converted from XML to Scaloid (for supported features)
• wraps everything in new classes/traits - it is hard to mix Scaloid with Java code
• some methods run on an UI thread
• no support for some newer SDK features (e.g. android.support.v4.widget.DrawerLayout)
• last update 2 months ago

Macroid

var userId = slot[EditText]

l[VerticalLinearLayout](
  w[TextView] <~ text("ID"),
  w[EditText] <~ wire(userId),
  w[Button] <~ text("Sign in") <~ On.click(signin(userId.get.getText))
) ~> padding(all = 20 dp)

Macroid

• maintained by 47deg
• as little verbosity as with Scaloid
• works with all Android components
• really nice support for async - UI actions as IO monad (unfortunately they don't work with for-comprehension)
• thread safety (as opposed to vanilla Android SDK)
• last update 3 months ago

Macroid

val action: Ui[Button] =
  (startButton <~ disable) ~
  (stopButton <~ enable)

import macroid.FullDsl._
runUi(action)

Protify

Functional programming on Android

Android

• stateful API
• allows and uses nulls
• imposes flow of data and way of handling actions
• many libraries use globals

Slick

• version 2 works
• SQLite driver
• see: github.com/pulsation/slick-android-example

Scalaz and Cats

• :)

Mutability and statefulness

Mutability and statefulness

• purely functional programming virtually impossible
• nothing prevent us from creating an abstraction layer