Hi, I'm trying to setup a channel producer like explained here (https://kotlinlang.org/docs/reference/coroutines/channels.html) - keyword: coroutines - but I don't know how I have to use a scope so that the

produce

method is available within `scan`:

@ObsoleteCoroutinesApi
    @ExperimentalCoroutinesApi
    @RequiresPermission(Manifest.permission.BLUETOOTH_ADMIN)
    fun scan(filters: List<ScanFilter>?, settings: ScanSettings): ReceiveChannel<ScanResult> {
        requireSafeSettings(settings)
        return produce(context) { // unresolvable reference
            val scanResultsChannel = Channel<ScanResult>(capacity = UNLIMITED)
            val scanCallback = ScanCallback(scanResultsChannel)
            scanner.startScan(filters, settings, scanCallback)
            scanResultsChannel.consumeEach { send(it) }
            scanResultsChannel.invokeOnClose { scanner.stopScan(scanCallback) }

            if (SDK_INT >= O_MR1 && scanCallback.isScanningTooFrequently()) {
                scanResultsChannel.close(ScanFailedException(SCAN_FAILED_SCANNING_TOO_FREQUENTLY))
            }
        }
    }

I call this method within

ScannerLiveData

class that extends from LiveData:

fun startScan() {
        if (isScanning) {
            return
        }

        scanChannel = scanner.scan(null, settings)

        scanChannel.consumeEach {  // unresolvable reference
            // Todo
        }

        isScanning = true
    }

My

ScannerLiveData

object gets injected in my

ScannerViewModel

where I simply call

startScan()

. I don't know how to provide a scope to use the

scan

method. I know there is a predefined

viewModelScope

...The only idea I have is to pass this scope down to

scan

method. Can someone help?

You have to think in term of lifecycle : should

ScannerLiveData

instances live longer that its

ViewModel

? If no, create instances of

ScannerLiveData

by passing the scope of the viewmodel. Otherwise, you have to define your own scope for your LiveData and cancel it when it is not longer required.

ScannerLiveData

doesn't live longer so I would pass the viewmodel scope to

ScannerLiveData

via constructor but will I have to pass the scope to

scan

method too?

Are you trying to reuse code from there? https://github.com/Beepiz/BleScanCoroutines

yes but you are using coroutines with experimental state so I couldn't use it with a newer Kotlin version

Yes, I didn't update it yet because I wasn't so happy with the API. I'll try to take time to make an update this night, I use a modified version successfully in a private project, it's good enough.

@Lilly Yes, you can start your producer coroutine with the following :

return scope.produce { ... }

Note that you need to pass a parameter to

produce

only if you want the producer coroutine to have some context (for example, move away from the main thread by passing

<http://Dispatchers.IO|Dispatchers.IO>

)

@louiscad Alright Sir. Btw...I'm not soo familiar with coroutines yet like you but is it neccessary to create the extra

scanResultsChannel

. Isn't there a possibility to just have one channel, i.e. create a channel outside of your library and pass it to

scan

and then to

ScanCallback

? @tseisel Thanks Sir and ty for the interesting bonus information 🙂

@Lilly I just released version 0.2.0 of BleScanCoroutines, with a simpler API, and it uses only one channel!

haha nice man! I will have a look tomorrow 🙂

@Lilly I'm not sure why you use coroutines here if it's to just end up with a pair of start and stop functions. My library is made so you scan, consuming the channel, taking advantage of being in a coroutine, and when you stop the channel, it is automatically closed. The scope of the consumption should be whatever best fit your needs, which would be one from ViewModel (cancelled in onCleared, which is automatically fone for you if you use the recently released viewmodel-ktx), or a child of it `from a

coroutineScope { … }

, or a coroutine builder. Note that

Flow

(aka. cold streams from kotlinx.coroutines) is coming and should be a better fit for that API, and when the API is stable enough, I'll likely update BleScanCoroutines for it.

@louiscad Hmm I can't consume the channel without a coroutine. When I try to iterate over the channel I get the message to use it within a coroutine.

scanChannel = scanner.scanChannel(null, settings)
        for (result in scanChannel) deviceDiscovered(result)

Btw I'm using the

viewModelScope

provided by

viewmodel-ktx

, just wasn't sure if it gets canceled automatically, but you're right.

@Lilly I was talking about using the raw API, without my library, when mentioning start/stop functions pair

@louiscad Sorry I can't follow you...do you suggest not to use your library in my case?

Yes, if you don't need a channel and don't need it in the coroutine world

Alright, thanks for your investigation. Btw I will use your BleGattCoroutine library. Keep going with the great work 🙂

I'm glad it's helpful 🙂