Android Keyboard Status Observable

KeyboardManager.kt

/**
 * Manages access to the Android soft keyboard.
 */
class KeyboardManager @Inject constructor(private val activity: Activity) {

  /**
   * Observable of the status of the keyboard. Subscribing to this creates a
   * Global Layout Listener which is automatically removed when this 
   * observable is disposed.
   */
  fun status() = Observable.create<KeyboardStatus> { emitter ->
    val rootView = activity.findViewById<View>(android.R.id.content)

    // why are we using a global layout listener? Surely Android 
    // has callback for when the keyboard is open or closed? Surely
    // Android at least lets you query the status of the keyboard? 
    // Nope! https://stackoverflow.com/questions/4745988/                                            
    val globalLayoutListener = ViewTreeObserver.OnGlobalLayoutListener {

      val rect = Rect().apply { rootView.getWindowVisibleDisplayFrame(this) }

      val screenHeight = rootView.height

      // rect.bottom is the position above soft keypad or device button.
      // if keypad is shown, the rect.bottom is smaller than that before.
      val keypadHeight = screenHeight - rect.bottom

      // 0.15 ratio is perhaps enough to determine keypad height.
      if (keypadHeight > screenHeight * 0.15) {
        emitter.onNext(KeyboardStatus.OPEN)
      } else {
        emitter.onNext(KeyboardStatus.CLOSED)
      }
    }

    rootView.viewTreeObserver.addOnGlobalLayoutListener(globalLayoutListener)

    emitter.setCancellable {
      rootView.viewTreeObserver.removeOnGlobalLayoutListener(globalLayoutListener)
    }
                                                                                
  }.distinctUntilChanged()
}

enum class KeyboardStatus {
  OPEN, CLOSED
}