伴侣对象的情况下对象

Question

我使用Scala的2.12，我试了一段代码，在2.11版本编码的，它不会再编译：

object MusicController { 
    sealed trait ControllerMsg 
    case object Play extends ControllerMsg 
    case object Stop extends ControllerMsg 
} 

// Music Controller 
class MusicController extends Actor { 
    def receive = { 
     case Play => 
      println("Music Started ...") 
     case Stop => 
      println("Music Stopped ...") 
    } 
} 

我有以下的编译器错误：

not found: value Play 
[error]   case Play => 
not found: value Stop 
[error]   case Stop => 

Answer 1

您需要导入MusicController的对象来说

object MusicController { 
    sealed trait ControllerMsg 
    case object Play extends ControllerMsg 
    case object Stop extends ControllerMsg 
} 

// Music Controller 
class MusicController extends Actor { 
    import MusicController._ // <-- IMPORT THIS 
    def receive = { 
     case Play => 
      println("Music Started ...") 
     case Stop => 
      println("Music Stopped ...") 
    } 
}