Observation of state change of View by Flow

Main.kt

// in Activity
override fun onCreate(savedInstanceState: Bundle?) {
  super.onCreate(savedInstanceState)  
  lifecycleScope.launchWhenCreated {
      editNickName.textChangeAsFlow()
        .map { it?.isNotEmpty() ?: false }
        .collect {
            sendButton.isEnabled = it
        }
}

// if you want to get 1 hot stream and n cold stream,
// you can use broadcastIn()
override fun onCreate(savedInstanceState: Bundle?) {
  super.onCreate(savedInstanceState)  
  lifecycleScope.launchWhenCreated {
    val textChange = editNickName.textChangeAsFlow().broadcastIn(this).asFlow()
    launch {
      textChange
          .map { it?.isNotEmpty() ?: false }
          .collect {
              sendButton.isEnabled = it
          }
    }
    launch {
      textChange
          .map { 140 - (it?.length ?: 0) }
          .collect { remain ->
              editNickNameLimit.text = "remain: $remain"
          }
    }
  }
}

TextViewExtension.kt

fun TextView.textChangeAsFlow() =
    flowViaChannel<String?> { channel ->
        channel.offer(text.toString())
        val textWatcher = addTextChangedListener {
            channel.offer(it?.toString())
        }
        channel.invokeOnClose {
            removeTextChangedListener(textWatcher)
        }
    }