Scala笔记1之配置使用Scala开发Android（基于Wire）

Scala配置步骤：

1. 打开AndroidStudio新建一个项目，为了能够尽可能踩坑涨姿势，选择支持Kotlin。
2. 只要正常的Android环境配置是OK，新建的项目肯定是没问题。配置如下：
   • gradle verison 5.4.1
   • kotlin version 1.3.50
   • gradle build tools 3.5.2
3. Scala配置
   • 根目录gradle配置Scala plugin

   classpath 'com.wire:gradle-android-scala-plugin:1.5.0'
   maven { url "https://dl.bintray.com/wire-android/third-party" }
   

   • 项目gradle应用plugin

   apply plugin: 'jp.leafytree.android-scala'
   

4. 解决上述配置产生的问题

解决配置问题

apply plugin: 'jp.leafytree.android-scala' 的问题

* What went wrong:
A problem occurred evaluating project ':app'.
> Failed to apply plugin [id 'jp.leafytree.android-scala']
   > Could not find matching constructor for: org.gradle.api.internal.file.DefaultSourceDirectorySetFactory(org.gradle.api.internal.file.BaseDirFileResolver, org.gradle.api.internal.file.collections.DefaultDirectoryFileTreeFactory)

应用Scala插件报错。

由于插件兼容的gradle过低导致的，降低项目配置的gradle version 即可。

gradle version 5.4.1 =》 4.10.2

PS: 由于Scala plugin 并未及时更新兼容最新版的Gradle version。SO 只能降低gradle 版本用来适配Scala plugin

gradle build tools 版本问题

* What went wrong:
A problem occurred evaluating project ':app'.
> Failed to apply plugin [id 'com.android.application']
   > Minimum supported Gradle version is 5.4.1. Current version is 4.10.2. If using the gradle wrapper, try editing the distributionUrl in /Users/qq/git/android/ScalaDemo/gradle/wrapper/gradle-wrapper.properties to gradle-5.4.1-all.zip

降低gradle版本之后，需要同步降低 gradle build tools 3.5.2 =》 3.2.1

Kotlin 插件版本

* What went wrong:
A problem occurred configuring root project 'ScalaDemo'.
> Could not resolve all artifacts for configuration ':classpath'.
   > Could not download httpclient.jar (org.apache.httpcomponents:httpclient:4.5.3)
      > Could not get resource 'https://jcenter.bintray.com/org/apache/httpcomponents/httpclient/4.5.3/httpclient-4.5.3.jar'.
         > Could not GET 'https://jcenter.bintray.com/org/apache/httpcomponents/httpclient/4.5.3/httpclient-4.5.3.jar'.
            > Remote host closed connection during handshake

需要同步修改 kotlin gradle plugin 1.3.50 => 1.3.10

ScalaCompileOptions

No such property: useAnt for class: org.gradle.api.tasks.scala.ScalaCompileOptions

当出现如上报错时，在项目目录的dependencies中配置如下：

dependencies{
    ScalaCompileOptions.metaClass.daemonServer = true
    ScalaCompileOptions.metaClass.fork = true
    ScalaCompileOptions.metaClass.useAnt = false
    ScalaCompileOptions.metaClass.useCompileDaemon = false
}

Setup Scala SDK

当尝试创建一个Scala Class时，AS会提示缺少Scala 的SDK，为了便于IDE做提示，我们需要点击之后，选择指定的Scala版本。如指定：2.11.12

Hello Word

完成上述配置之后，使用AS作为IDE的配置基本上差不多了。在新建的Scala文件中让Word Hello起来！

在熟悉的源码目录 java 目录下创建一个Scala Class文件即可。

class HelloWord {

  def hello(): Unit = {
    println("Hello Scala! ")
  }
}

然后通过AS默认生成的Java单元测试直接跑起来即可：

class ExampleUnitTest {
    @Test
    fun addition_isCorrect() {

        HelloWord().hello()

        assertEquals(4, 2 + 2)
    }
}

Hello Scala!

最终run的控制台中会输出如上。