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Tuesday, April 22, 2014

Android API 8 is incompatible with mutable collections from Scala 2.11

I've found that newly introduced class scala.collection.mutable.AnyRefMap and mutable.LongMap are using java.util.Arrays.copyOf(...), that is available only on Android API level 9 and above. This means that your Android app might not work with Froyo devices if you build it with Scala 2.11. Because the current market share of the API level < 9 is less than 1 percent, this limitation is not serious.

However, if you stick to support older Android devices, here is a workaround:
  • Add -dontwarn scala.collection.mutable.** in your proguard settings.
  • Do not use scala.collection.mutable.LongMap and mutable.AnyRefMap. Make sure these classes not be called in transitive way.

Sunday, April 20, 2014

Scaloid 3.3 is released

Today I released Scaloid 3.3. This version achieves some feature enhancements including:

Scala 2.11 support

Scala 2.11 is out! We release this version of Scaloid in both of Scala 2.10 and 2.11.

Press-and-Hold action

We support press-and-hold action listener for any subtype of android.view.View object.

Any return type of event listener is accepted

Please refer to issue #78

Scaloid is released to central maven repository.

For a maven project:
or for an sbt project:
libraryDependencies += "org.scaloid" %% "scaloid" % "3.3-8"

Saturday, April 19, 2014

Press-and-hold action on Android

Sometimes we need to receive repeated callback when a user pressing a button continuously. For example, when we make a number picker, press-and-hold on "+" button will constantly increase the number.

Android does not support this explicitly, but we can handle this behavior with postDelayed event. Here is a link to a code snippet doing this:

This works fine, but a little remaining problem is that this code should be encapsulated to be reused in other places. I wrote the following trait doing the encapsulation:

trait PressAndHoldable {
  def basis: android.view.View

  class PressAndHoldListener(interval: Int, onPressed: () => Unit) extends View.OnTouchListener with View.OnLongClickListener {
    var autoIncrementing: Boolean = false
    private val repeatUpdateHandler = new android.os.Handler()

    override def onTouch(v: View, event: MotionEvent): Boolean = {
      if (event.getAction == MotionEvent.ACTION_UP && autoIncrementing) {
        autoIncrementing = false

    override def onLongClick(p1: View): Boolean = {
      autoIncrementing = true RptUpdater)

    class RptUpdater extends Runnable {
      override def run() {
        if (autoIncrementing) {
          repeatUpdateHandler.postDelayed(this, interval)

  def onPressAndHold(interval: Int, onPressed: => Unit) {
    val listener = new PressAndHoldListener(interval, () => onPressed)

This trait is added on Scaloid 3.3 release. So you can just use onPressAndHold method for any android.view.View objects:
val num = STextView("0")
SButton("Increase").onPressAndHold(100, num.text = (num.text.toString.toInt + 1).toString)