gradle-android-scala-plugin

gradle-android-scala-plugin adds scala language support to official gradle android plugin. See also sample projects at https://github.com/saturday06/gradle-android-scala-plugin/tree/master/sample

Table of Contents generated with DocToc

• Supported versions
• Installation
  • 1. Add buildscript's dependency
  • 2. Apply plugin
  • 3. Add scala-library dependency
  • 4. Put scala source files
  • 5. Implement a workaround for DEX 64K Methods Limit
    • 5.1. Option 1: Use ProGuard
    • 5.2. Option 2: Use MultiDex
      • 5.2.1. Setup application class if you use customized one
• Configuration
• Complete example of build.gradle with manually configured MultiDexApplication
• Changelog

Supported versions

Scala	Gradle	Android Plugin	compileSdkVersion	buildToolsVersion
2.11.12	4.10.2	3.2.1	21, 22, 23	21.1.2, 22.0.1

If you want to use older build environment, please try android-scala-plugin-1.3.2

Installation

1. Add buildscript's dependency

build.gradle

buildscript {
    
    repositories {
        maven {
            url "https://dl.bintray.com/wire-android/third-party"
        }
    }   

    dependencies {
        classpath "com.android.tools.build:gradle:3.6.4"
        classpath "com.wire.gradle:gradle-android-scala-plugin:1.6"
    }
}

2. Apply plugin

build.gradle

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

3. Add scala-library dependency

The plugin decides scala language version using scala-library's version.

build.gradle

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

4. Put scala source files

Default locations are src/main/scala, src/androidTest/scala. You can customize those directories similar to java.

build.gradle

android {
    sourceSets {
        main {
            scala {
                srcDir "path/to/main/scala" // default: "src/main/scala"
            }
        }

        androidTest {
            scala {
                srcDir "path/to/androidTest/scala" // default: "src/androidTest/scala"
            }
        }
    }
}

5. Implement a workaround for DEX 64K Methods Limit

The Scala Application generally suffers DEX 64K Methods Limit. To avoid it we need to implement one of following workarounds.

5.1. Option 1: Use ProGuard

If your project doesn't need to run androidTest, You can use proguard to reduce methods.

Sample proguard configuration here:

proguard-rules.txt

-dontoptimize
-dontobfuscate
-dontpreverify
-dontwarn scala.**
-ignorewarnings
# temporary workaround; see Scala issue SI-5397
-keep class scala.collection.SeqLike {
    public protected *;
}

From: hello-scaloid-gradle

5.2. Option 2: Use MultiDex

Android comes with built in support for MultiDex. You will need to use MultiDexApplication from the support library, or modify your Application subclass in order to support versions of Android prior to 5.0. You may still wish to use ProGuard for your production build.

Using MultiDex with Scala is no different than with a normal Java application. See the Android Documentation and MultiDex author's Documentation for details.

It is recommended that you set your minSdkVersion to 21 or later for development, as this enables an incremental multidex algorithm to be used, which is significantly faster.

build.gradle

repositories {
    jcenter()
}

android {
    defaultConfig {
        multiDexEnabled true
    }
}

dependencies {
    implementation "org.scala-lang:scala-library:2.11.7"
    implementation "com.android.support:multidex:1.0.2"
}

Change application class.

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="jp.leafytree.sample">
    <application android:name="android.support.multidex.MultiDexApplication">
</manifest>

If you use customized application class, please read next section.

To test MultiDexApplication, custom instrumentation test runner should be used. See also https://github.com/casidiablo/multidex/blob/publishing/instrumentation/src/com/android/test/runner/MultiDexTestRunner.java

build.gradle

android {
    defaultConfig {
        testInstrumentationRunner "com.android.test.runner.MultiDexTestRunner"
    }
}

dependencies {
    implementation "org.scala-lang:scala-library:2.11.7"
    implementation "com.android.support:multidex:1.0.2"
    androidTestImplementation "junit:junit:4.12"
}

5.2.1. Setup application class if you use customized one

Since application class is executed before multidex configuration, Writing custom application class has stll many pitfalls.

The application class must extend MultiDexApplication or override Application#attachBaseContext like following.

MyCustomApplication.scala

package my.custom.application

import android.app.Application
import android.content.Context
import android.support.multidex.MultiDex

object MyCustomApplication {
  var globalVariable: Int = _
}

class MyCustomApplication extends Application {
  override protected def attachBaseContext(base: Context) = {
    super.attachBaseContext(base)
    MultiDex.install(this)
  }
}

You need to remember:

NOTE: The following cautions must be taken only on your android Application class, you don't need to apply this cautions in all classes of your app

• The static fields in your application class will be loaded before the MultiDex#installbe called! So the suggestion is to avoid static fields with types that can be placed out of main classes.dex file.
• The methods of your application class may not have access to other classes that are loaded after your application class. As workaround for this, you can create another class (any class, in the example above, I use Runnable) and execute the method content inside it. Example:

  override def onCreate = {
    super.onCreate

    val context = this
    new Runnable {
      override def run = {
        variable = new ClassNeededToBeListed(context, new ClassNotNeededToBeListed)
        MyCustomApplication.globalVariable = 100
      }
    }.run
  }

This section is copyed from README.md for multidex project

Configuration

You can configure scala compiler options as follows:

build.gradle

tasks.withType(ScalaCompile) {
    // If you want to use scala compile daemon
    scalaCompileOptions.useCompileDaemon = true
    // Suppress deprecation warnings
    scalaCompileOptions.deprecation = false
    // Additional parameters
    scalaCompileOptions.additionalParameters = ["-feature"]
}

Complete list is described in http://www.gradle.org/docs/current/dsl/org.gradle.api.tasks.scala.ScalaCompileOptions.html

Complete example of build.gradle with manually configured MultiDexApplication

build.gradle

buildscript {
    repositories {
        mavenCentral()
        maven {
            url "https://dl.bintray.com/wire-android/third-party"
        }
    }

    dependencies {
        classpath "com.android.tools.build:gradle:3.6.4"
        classpath "com.wire.gradle:gradle-android-scala-plugin:1.6"
    }
}

repositories {
    jcenter()
}

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

android {
    compileSdkVersion "android-22"
    buildToolsVersion "22.0.1"

    defaultConfig {
        targetSdkVersion 22
        testInstrumentationRunner "com.android.test.runner.MultiDexTestRunner"
        versionCode 1
        versionName "1.0"
        multiDexEnabled true
    }

    flavorDimensions "default"

    productFlavors {
        dev {
            minSdkVersion 21 // To reduce compilation time
        }

        prod {
            minSdkVersion 9
        }
    }

    sourceSets {
        main {
            scala {
                srcDir "path/to/main/scala" // default: "src/main/scala"
            }
        }

        androidTest {
            scala {
                srcDir "path/to/androidTest/scala" // default: "src/androidTest/scala"
            }
        }
    }
}

dependencies {
    implementation "org.scala-lang:scala-library:2.11.7"
    implementation "com.android.support:multidex:1.0.2"
    androidTestImplementation "junit:junit:4.12"
}

tasks.withType(ScalaCompile) {
    scalaCompileOptions.deprecation = false
    scalaCompileOptions.additionalParameters = ["-feature"]
}

Changelog

• 1.4 Support android plugin 1.1.3. Manual configuration for dex task is now unnecessary (contributed by sgrif)
• 1.3.2 Fix unexpected annotation processor's warnings
• 1.3.1 Support android plugin 0.12.2
• 1.3 Incremental compilation support in scala 2.11
• 1.2.1 Fix binary compatibility with JDK6
• 1.2 Incremental compilation support in scala 2.10 / Flavors support
• 1.1 MultiDexApplication support
• 1.0 First release