I'm using MVVM with jetpack compose, and I need to...

# compose

[Pablo]

I'm using MVVM with jetpack compose, and I need to make a call to Geocoder in my viewmodel. But now, the Geocoder class returns the response on a Listenner. It sounds rare to use a listener like in the old days of android views, but inside a viewmodel of compose. Is correct to do it? I'm attaching the sample in the thread

[Pablo]

fun transformStringLocationIntoLatLng(context: Context, address: String, addressType: AddressType) {
    viewModelScope.launch(Dispatchers.IO) {
        _uiState.update { currentState -> currentState.copy(loading = true) }

        val geocoder = Geocoder(context)
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
            geocoder.getFromLocationName(address, 1, object : Geocoder.GeocodeListener {
                override fun onGeocode(addresses: List<Address>) {
                    if (addresses.isNotEmpty()) {
                        val location = addresses[0]
                        val latLng = LatLng(location.latitude, location.longitude)

                        when (addressType) {
                            AddressType.ORIGIN ->
                                _uiState.update { currentState -> currentState.copy(loading = false, originLocation = latLng)}
                            AddressType.DESTINATION ->
                                _uiState.update { currentState -> currentState.copy(loading = false, destinationLocation = latLng)}
                        }
                    }
                }
                override fun onError(errorMessage: String?) {
                    Log.d("XXXX", "GeocodeListener ERROR: $errorMessage")
                }
            })
        } else {
            val addresses = geocoder.getFromLocationName(address, 1)
            if (addresses?.isNotEmpty() == true) {
                val location = addresses[0]
                val latLng = LatLng(location.latitude, location.longitude)

                when (addressType) {
                    AddressType.ORIGIN ->
                        _uiState.update { currentState -> currentState.copy(loading = false, originLocation = latLng)}
                    AddressType.DESTINATION ->
                        _uiState.update { currentState -> currentState.copy(loading = false, destinationLocation = latLng)}
                }
            }
        }
    }
}

[François]

You can convert your listener in coroutine, it’s not difficult;

[Pablo]

you mean doing this?

[Pablo]

suspendCancellableCoroutine { continuation ->
        val geocoder = Geocoder(context, Locale.getDefault())
        try {
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
                geocoder.getFromLocationName(address, 1, object : Geocoder.GeocodeListener {
                    override fun onGeocode(addresses: List<Address>) {
                        if (addresses.isNotEmpty()) {
                            val location = addresses[0]
                            continuation.resume(LatLng(location.latitude, location.longitude))
                        } else {
                            continuation.resume(null)
                        }
                    }

                    override fun onError(errorMessage: String?) {
                        continuation.resumeWithException(Exception(errorMessage))
                    }
                })

[Pablo]

I still see that code using a listener.... so no changes, it is still using a listener inside mvvm and compose

[François]

Your listener is behind a Coroutine and make your viewmodel cleaner.
Move your new code outside your viewmodel

[Pablo]

can you clarify what you mean please¿?

[François]

If you’re API can only use listener, it’s fine.
• Wrap it inside a coroutine like you show
• Make a reusable function of it.

[Pablichjenkov]

Or maybe Flow.callbackFlow

[Pablo]

François but I can do more or less the same without using the corutine and I still have the listener wrapping it into a corutine so I feel that no changes

[Pablo]

Pablichenko how to achieve it with that

[Pablo]

maybe doing that the listenner dissapear?

[Pablo]

or maybe simply is correct to use a listener inside a MVVM compose viewmodel?

[Pablichjenkov]

Ask any llm for an example of it

[Pablichjenkov]

Or any direct text matcher like Google search

[Pablo]

well, for this case I prefeer human interaction

[Pablo]

knowing if is a correct approach to use a listener inside a MVVM compose viewmodel is not a simple google search

[Pablichjenkov]

There is nothing wrong with that. Just ensure you unsubscribe from the event source(in this case the location provider) when the ViewModel is cleared, onClear()

[Pablo]

ummm

[Pablo]

I don't think it's possible to unsubscribe it

[Pablo]

or at least don't see a method for that

[Pablo]

finally I migrated it to suspendCancellableCoroutine. Because then I can move it to a domain UseCase and simply calling it as a suspend function and update uistate with the result

[Pablo]

but now I wonder what will happen if the vm is closed, maybe it will magically unsubscribe the listener?

[Pablichjenkov]

Humm but is your listener receiving only one event or multiple events?
In the case of one event this is fine. I thought it received multiple calls hince my suggestion to use callbackFlow. But for a one event operation you don't need to unsubscribe or anything like that. This is enough.

[Pablichjenkov]

If you use viewModelScope to execute the coroutine it will cancel in onClear, you are good

[Pablo]

great

[Pablo]

thanks