hi ya'll! I'm a compose noob (but a fair amount o...

# compose

[Kevin Hester]

hi ya'll! I'm a compose noob (but a fair amount of kotlin experience) who is trying to convert my app over to compose - partly as an experiment and partly because I love reactive frameworks.

A question: What is the best "compose way" to run code when the view changes? i.e. based on changes to a "screen" model variable it nicely changes which content gets generated. But when I change to my "bluetooth scan screen" I need to start the android BTLE scan operation (with a callback that gets invoked to add elements to my model "list of bluetooth devices"). When that screen goes away (because the screen variable got changed). I need to run some code to stop and destroy the BLE scanner class.

when (screen) {
    is Screen.Home -> HomeContent()
    is Screen.SelectRadio -> BTScanScreen()
    // Question: how to get hooks invoked when this screen gets shown/removed?
    // i.e. I need to start/stop a bluetooth scan operation. depending on the
    // appearance/disappearance of this screen.
}

[Adam Powell]

You're probably looking for either onCommit or onActive : https://developer.android.com/reference/kotlin/androidx/compose/package-summary.html#onactive

[Kevin Hester]

OOH SUPER COOL - that is perfect. Thanks so much!

[Adam Powell]

do note that these are lifecycle of the composition, not related to activity lifecycle. If you want things to stop as part of onStop in the LifecycleObserver sense, you'll need to combine those two things together. Some out of the box API will be around for this later

[Kevin Hester]

thanks for that extra note. You're awesome (and great framework you've made). I think onActive with its onDispose callback is perfect for my case. After I have it working and cleaned up a bit, I'll send the .kt to you. Feel free to use it if you want to provide a small self contained demo of how to make Compose work with sideeffectish low level android services.