ReactiveX in scala-swing doesn't work?

Question

I'm newbie to reactivex, and try to use it with scala-swing.

My code is quite simple, but it doesn't work:

import rx.lang.scala.Observable

import scala.swing.{Frame, MainFrame, SimpleSwingApplication, TextField}

object HelloReactiveX extends SimpleSwingApplication {

  val input = new TextField()

  override def top: Frame = new MainFrame {
    title = "Hello, reactivex"
    contents = input
  }

  val stream = Observable[String] { subscriber =>
    println("before input.subscribe")
    input.subscribe {
      case _ => {
        println("input changed: " + input.text)
        subscriber.onNext(input.text)
      }
    }
    println("after input.subscribe")
  }

  stream.subscribe(t => println("###: " + t))

}

The dependency is:

"org.scala-lang.modules" %% "scala-swing" % "1.0.1",
"io.reactivex" %% "rxscala" % "0.25.0",

The strange thing is there is nothing printed to the console!

Is there anything wrong in my code?

PS: The live project is here https://github.com/freewind/scala-swing-demo/blob/fc79c5b65e6fecc21d3894888d336d8f5204f62e/src/main/scala/scalaswing/HelloReactiveX.scala