How to force to execute Future callback function in Android UIThread.

UIDemoActivity.scala

import scala.concurrent._
import ExecutionContext.Implicits.global
import android.util.Log
import android.widget.TextView

class UIDemoActivity extends Activity {

  override def onCreate(bundle: Bundle) {
    super.onCreate(bundle)
    val tv = new TextView(this)
    setContentView(tv)

    //pass ExecutionaContext.Implicits.global Implicitly.
    val x: Future[Long] = future {
       Log.d("FutureTest", "Future task is executed at:"+Thread.currentThread().getName)
      val args = List.range(1, 1000000L)
      args.sum
    }
    Log.d("FutureTest", "Future instance is created at:"+Thread.currentThread().getName)
    
    //pass UIExecutionContext eplicitly.
    val mine = new UIExecutionContext(this)
    x.onSuccess {
      case count =>
         Log.d("FutureTest", "Future task callback is executed at:"+Thread.currentThread().getName)
        tv.setText(tv.getText + " onSuccess!:"+count.toString )
    }(mine)
    
    /**
     * LogCat.
     * Future instance is created at:main
     * Future task is executed at:ForkJoinPool-1-worker-5
     * Future task callback is executed at:main
     */
  }
}

UIExecutionContext.scala

import concurrent.ExecutionContext
import android.app.Activity

class UIExecutionContext(activity:Activity) extends ExecutionContext{
  def execute(runnable: Runnable): Unit = activity.runOnUiThread(runnable)

  def reportFailure(t: Throwable): Unit = t match{
    case NonFatail(e) => e.printStackTrace()
    case _ => throw t
  }
}