rememberCameraPositionState() should accept inputs

[svenjacobs]

I noticed that in version 2.7.0 of maps-compose the function rememberCameraPositionState does not accept any inputs although it just delegates to rememberSaveable, which has vararg inputs: Any?. Is this a deliberate design decision?

I have a situation where the value actually should be recreated because latitude and longitude change after the user has selected a different location.

I'm happy to provide a pull request if this is a desired change.

[svenjacobs]

The same applies to rememberMarkerState(). Maybe there are more remember*() functions in the library that I don't use.

[bubenheimer]

I think the idea, at least in the case of MarkerState, is to handle any changes via LaunchedEffect, so that the underlying GoogleMap model Marker will not be recreated, but updated:

    val markerState = rememberMarkerState()

    LaunchedEffect(coords) { markerState.position = coords }

I expect it will change at some point to make it less edgy: #149

[svenjacobs]

Good point. In case of rememberCameraPositionState() I tried to work around it by using

val pos = remember(latitude, longitude) { LatLng(latitude, longitude) }
val cameraPositionState = rememberSaveable(pos, saver = CameraPositionState.Saver) {
    CameraPositionState(
        position = CameraPosition.fromLatLngZoom(pos, 17f),
    )
}

which works as expected but applying the same pattern to rememberMarkerState() did not work. The inner workings of Marker probably don't take state changes into account at the moment.

[arriolac]

rememberCameraPositionState does accept inputs—both key, the key to use for rememberSaveable, and init, a function literal with receiver so you can provide the same init values CameraPositionState accepts. But perhaps I'm misunderstanding?

So you should be able to do:

val cameraPositionState = rememberCameraPositionState {
  position = CameraPosition.fromLatLngZoom(pos, 17f)
}

Same comment for MarkerState.

[svenjacobs]

The functions have a key argument, that's correct, but not an inputs argument. Quoting documentation of rememberSaveable:

inputs: A set of inputs such that, when any of them have changed, will cause the state to reset and init to be rerun

key: An optional key to be used as a key for the saved value. If not provided we use the automatically generated by the Compose runtime which is unique for the every exact code location in the composition tree

I'm talking about inputs because I'd like to reset the state when for instance latitude or longitude change.

val position = rememberCameraPositionState(latitude, longitude) { ... }

[arriolac]

Gotcha—yes I misunderstood your question. I don't see any reasons for inputs not to be exposed in Maps Compose remember*() functions. Feel free to send a PR for it @svenjacobs

[svenjacobs]

I can create a PR for rememberCameraPositionState but for rememberMarkerState it is a bit more complicated. See comments here, here and this issue.

[arriolac]

Adding inputs to rememberMarkerState will not recreate the Marker so in theory you can expose inputs to both remember functions. But, recreating CameraPositionState needs to set the associated GoogleMap and MarkerState needs to set the correct internal Marker. These side effects make implementing this feature not so straightforward actually.. I suggest holding off on the pull request for that reason.

[PeterAttardo]

I just ran into the same issue, and it took me about three hours of debugging to realize that key in remember and key in rememberSaveable aren't the same, and that despite rememberSaveable calling through to remember, it doesn't pass key to key but rather inputs to key. This is mostly hidden from the typical compose user because remember and rememberSaveable behave the same as long as you use positional arguments, which users will default to 99% of the time.

maps-compose's lack of a positional inputs means that the positional argument gets funneled into rememberSaveable's key argument, which most users have probably never used before, and aren't expecting. The above naming confusion means that even if they check the signature of rememberCameraPositionState, they won't notice anything amiss, because of the natural assumption that key means key universally throughout compose's remember paradigm; not realizing that in rememberSaveable key is not key, but rather inputs is key.

Providing a 1:1 match with rememberSaveable's signature will at least minimize the confusion, and keep the remaining fault with the underlying compose naming, where it belongs.