Android keyboard state observer.

KeyboardObserver.kt

/**
 * Android keyboard state observer.
 * For portrait orientation only.
 * https://bit.ly/3flvZar
 * 2020 intelligence.worker@gmail.com.
 *
 * Example of usage:
 * viewLifecycleOwner.lifecycleScope.launch {
 *      this@MyFragment.view?.run {
 *          KeyboardObserver().observe(your_root_view_here).distinctUntilChanged().collect { ... }
 *      }
 * }
 */
class KeyboardObserver {

    private var mRootView: View? = null

    fun observe(rootView: View): Flow<KeyboardData> = callbackFlow {
        mRootView = rootView

        val listener = ViewTreeObserver.OnGlobalLayoutListener {
            mRootView?.run {
                val rootHeight = rootView.height
                val rect = Rect().apply { rootView.getWindowVisibleDisplayFrame(this) }
                val keyboardHeight = rootHeight - (rect.bottom - rect.top)
                if (keyboardHeight > rootHeight * MIN_KEYBOARD_HEIGHT_RATIO) {
                    offer(KeyboardData(KeyboardStatus.OPENED, keyboardHeight))
                } else {
                    offer(KeyboardData(KeyboardStatus.CLOSED, keyboardHeight))
                }
            }
        }
        mRootView?.viewTreeObserver?.addOnGlobalLayoutListener(listener)

        awaitClose {
            mRootView?.viewTreeObserver?.removeOnGlobalLayoutListener(listener)
        }
    }

    companion object {
        // ratio is perhaps enough to determine keypad height
        const val MIN_KEYBOARD_HEIGHT_RATIO = 0.15
    }
}

enum class KeyboardStatus {
    OPENED, CLOSED
}

data class KeyboardData(
    val status: KeyboardStatus,
    val keyboardHeight: Int
) {
    val isClosed: Boolean
        get() = status == KeyboardStatus.CLOSED

    val isOpened: Boolean
        get() = status == KeyboardStatus.OPENED
}