CompositeOnFocusChangeListener.kt

class CompositeOnFocusChangeListener constructor(
  vararg listeners: OnFocusChangeListener
) : OnFocusChangeListener, MutableSet<OnFocusChangeListener> by listeners.toMutableSet() {

  override fun onFocusChange(view: View, hasFocus: Boolean) {
    forEach { it.onFocusChange(view, hasFocus) }
  }
}

fun View.addOnFocusChangeListener(listener: OnFocusChangeListener) {
  val compositeFocusChangeListener =
    (onFocusChangeListener as? CompositeOnFocusChangeListener) ?: CompositeOnFocusChangeListener().apply {
      onFocusChangeListener?.let(::add)
      onFocusChangeListener = this
    }
  compositeFocusChangeListener.add(listener)
}

fun View.removeOnFocusChangeListener(listener: OnFocusChangeListener) {
  (onFocusChangeListener as? CompositeOnFocusChangeListener)?.remove(listener)
}