Is it possible to pass a value from a BroadcastRec...

# compose

[Nat Strangerweather]

Is it possible to pass a value from a BroadcastReceiver to a Composable? If so, how? If I use an intent and putExtra, my Composable is not in an Activity so I'm stuck. 🤔

[nglauber]

You can do this (inside your composable function):

val context = AmbientContext.current
onActive {
    val broadcast = object: BroadcastReceiver() {
        override fun onReceive(context: Context?, intent: Intent?) {
            //intent?.getStringExtra("param") ?: ""
        }
    }
    context.registerReceiver(broadcast, IntentFilter("SOME_ACTION"))

    onDispose {
        context.unregisterReceiver(broadcast)
    }
}

[Adam Powell]

s/`onActive`/`DisposableEffect`/, but yes, in general, this.

[Adam Powell]

(onActive, onCommit, onDispose, etc. are going away soon in favor of the newer Effect composables)

[nglauber]

@Adam Powell is this the recommended solution?

val context = AmbientContext.current
val broadcast = remember {
    object: BroadcastReceiver() {
        override fun onReceive(context: Context?, intent: Intent?) {
            pressed(intent?.getStringExtra("key") ?: "")
        }
    }
}
DisposableEffect(subject = broadcast, effect = {
    context.registerReceiver(broadcast, IntentFilter("SOME_ACTION"))

    onDispose {
        context.unregisterReceiver(broadcast)
    }
})

[Adam Powell]

You can still keep the receiver inside the effect block (and I would) - context would be a valid subject here as it's what you're registering the receiver with. You should also consider what pressed is here. If it's a lambda param to the function you likely want something like:

val currentPressed by rememberUpdatedState(pressed)
val context = AmbientContext.current
DisposableEffect(context) {
  val broadcast = ... currentPressed(...) ...
  ...
}

[nglauber]

Great! this pressed is a lambda, but i just use this name to help here quickly… 😛

[Adam Powell]

rememberUpdatedState is specifically for this kind of usage, when you need composition to update something used by a long-lived object without recreating that long-lived object and potentially restarting some sort of heavyweight registration or subscription. Also useful for things like LaunchedEffect that suspend over time if you don't want to restart the whole coroutine.

[Adam Powell]

(and by extension, Modifier.pointerInput {})

[nglauber]

Great! I tried it here and worked fine 👏

[Nat Strangerweather]

Oh wow, thanks for this! I've been trying to solve this for about two weeks... Lol. 😂

[Nat Strangerweather]

So here:

DisposableEffect(context) {
        val broadcast = object : BroadcastReceiver() {
            override fun onReceive(context: Context?, intent: Intent?) {
                val code = codesProvider.getInterruptionFilter(context!!)
            }
        }
        context.registerReceiver(broadcast, intentFilter)
        onDispose {
            context.unregisterReceiver(broadcast)
        }
    }

How does code reach the actual Composable to be used?

[nglauber]

once you do this and the sendBroadcast is called, your code will be received.

[Adam Powell]

For perhaps more complete context based on the above,

@Composable fun MyBroadcastReceiver(
    param1: T1,
    param2: T2,
    receiver: (code: Int) -> Unit
) {
    val context = AmbientContext.current
    val currentReceiver by rememberUpdatedState(receiver)
    DisposableEffect(context, param1, param2) {
        val intentFilter = IntentFilter().apply {
            // add actions/filter params based on param1/param2
        }
        val broadcast = object : BroadcastReceiver() {
            override fun onReceive(context: Context?, intent: Intent?) {
                val code = codesProvider.getInterruptionFilter(context!!)
                currentReceiver(code)
            }
        }
        context.registerReceiver(broadcast, intentFilter)
        onDispose {
            context.unregisterReceiver(broadcast)
        }
    }
}

[Adam Powell]

Note:
1. The use of rememberUpdatedState to let composition change the receiver callback that is invoked with code when the BroadcastReceiver receives a broadcast without unregistering and reregistering the underlying BR
2. Parameters to the constructed IntentFilter become keys to the DisposableEffect, because we do need to unregister and reregister the BR if the IntentFilter we need to build changes

[Adam Powell]

functions like the above are common, and similar to the kinds of bridging functions between callbacks and coroutines that you would build with suspendCancellableCoroutine