I’m trying to create a flow from an EditText change in Android, I’m using `flow {…}` builder, So I’m...

# coroutines

[Mohamed Ibrahim]

I’m trying to create a flow from an EditText change in Android, I’m using flow {…} builder, So I’m creating a watcher inside it here is the code, my question is how I clear inner listeners when flow canceled ?

fun EditText.textChangesFlow(): Flow<TextViewTextChangeEvent> {
    flow<TextViewTextChangeEvent> {
        val watcher = object : TextWatcher {
            override fun afterTextChanged(s: Editable?) {
                emit(TextViewTextChangeEvent(s.toString()))
            }

            override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {
            }

            override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {
            }
        }
        addTextChangedListener(watcher)
         //how to call this when flow is canceled or finished
        //removeTextChangedListener(watcher)

    }
}

[streetsofboston]

Add an awaitClose { … clear inner listeners here … } at the end of your flow { … } lambda:

flow<TextViewTextChangedEvent> {
    ...
    ...
    awaitClose { removeTextChangedListener(watcher) }
  }

[kevin.cianfarini]

You must use channelFlow not flow. Within the scope of channelFlow you can use awaitClose. You must also change emit to send

channelFlow<TextViewTextChangedEvent> {
    ...
    ...
    awaitClose { removeTextChangedListener(watcher) }
  }

[Mohamed Ibrahim]

Do I need to make textChangesFlow suspend function, I have a compile error with send() and emit()

[kevin.cianfarini]

The scope inside channel flow should be suspend. So I wouldn't think so

[streetsofboston]

But the callback afterTextChanged is not suspend. So yes, either use offer(…) or wrap it inside a launch: launch { send(…) } .

[Mohamed Ibrahim]

I used launch{...} but is it safe to call?

[streetsofboston]

Not sure what you mean by ‘safe’?

[streetsofboston]

But creating Coroutines (using launch or async) is cheap, if you were worrying about that.

[tseisel]

I'd suggest using callbackFlow instead of channelFlow. While both provide exactly the same behavior, callbackFlow makes the intent clearer in this case. Also, since 1.3.4 there is a lint warning with callbackFlow that notifies you if you forget about awaitClose.

[dekans]

@hellman wrote a blog post about it:
https://www.hellsoft.se/instant-search-with-kotlin-coroutines/