RxAndroidBle - How to disconnect all connected devices?

Question

I am using awesome rxandroidble library for BLE control.
I keep connection between activities. Before I start scanning, I want to disconnect all connected devices first. Sometimes It is not working if there are many connections. This is the solution I am using:

public void doScan() {

    if (isScanning()) return;

    // disconnect all connected devices first:
    while(BleController.getDefault().getDisconnectTriggerSubject().hasObservers()){
        BleController.getDefault().getDisconnectTriggerSubject().onNext(null);
    }

    scanSubscription = rxBleClient.scanBleDevices(
            new ScanSettings.Builder()
                    .setScanMode(ScanSettings.SCAN_MODE_LOW_LATENCY)
                    .setCallbackType(ScanSettings.CALLBACK_TYPE_ALL_MATCHES)
                    .build(),
            new ScanFilter.Builder()
                    // add custom filters if needed
                    .build()
    )
            .filter(rxBleScanResult -> !TextUtils.isEmpty(rxBleScanResult.getBleDevice().getName()))
            .observeOn(AndroidSchedulers.mainThread())
            .doOnUnsubscribe(this::clearSubscription)
            .subscribe(resultsAdapter::addScanResult, this::onScanFailure);

    updateButtonUIState();

}

BleController is initialized with the main application's context and keeps the connectionObservable, disconnectTriggerSubject, rxBleClient.

What can be the better solution? Any help would be appreciated!

score 2 · Accepted Answer · answered Jan 16 '18 at 10:15

From your post I can see that you are mixing the BLE scanning/connection logic with the UI/Activity logic. This may be a problem to manage connections correctly.

What you could do is to put all the BLE logic to your BleController which already has a good name but it seems that in your situation is rather a BleObjectsContainer.

For instance you could only expose from the BleController only observables that are fulfilling your specific use-cases in a way that the Activities do not need to handle. i.e. Your BleController could handle scanning:

private final BehaviorRelay<Boolean> isScanningPublishRelay = BehaviorRelay.create(false); // a relay (that cannot emit an error) that emits when a scan is ongoing

private Observable<ScanResult> scanDevicesWithNonNullNameObs = rxBleClient.scanBleDevices(new ScanSettings.Builder().build())
        .filter(scanResult -> !TextUtils.isEmpty(scanResult.getBleDevice().getName()))
        .doOnSubscribe(() -> isScanningPublishRelay.call(true)) // when scan is subscribed/started emit true
        .doOnUnsubscribe(() -> isScanningPublishRelay.call(false)) // when scan is stopped emit false
        .subscribeOn(AndroidSchedulers.mainThread()) // the above emissions will happen on the same thread. should be serialized
        .unsubscribeOn(AndroidSchedulers.mainThread()) // the above emissions will happen on the same thread. should be serialized
        .share(); // share this observable so no matter how many places in the code will subscribe the scan is started once and `isScanningPublishRelay` is called once

public Observable<ScanResult> scanDevicesWithNonNullName() { // getter for the scan observable
    return scanDevicesWithNonNullNameObs;
}

And besides of scanning it would also handle your specific use-cases for each Activity that needs it:

class ScanInProgress extends Throwable {
    // ...
}

public Observable<YourActivityUseCaseModel> doYourSpecificStuff(Observable<RxBleConnection> connectionObservable) {
    return Observable.merge(
            connectionObservable,
            isScanningPublishRelay
                    .takeFirst(aBoolean -> aBoolean)
                    .flatMap(ignored -> Observable.error(new ScanInProgress())) // this will only emit an error when a scan is ongoing
    )
            .flatMap(...); // do the rest of your stuff
}

This way in your activities you would only need to subscribe to whatever model they need and handle the BLE in a single place that is dedicated for it (BleController).

In the above example you need to provide the Observable<RxBleConnection> but it can be achieved in many different ways and could managed in BleController as well so it would not be exposed in the interface.

Thank you very much for your answer. It is very useful. I have never used `BehaviorRelay` and `Observable.merge()`. And yes, later I will refactor my code, all the ble controls will be inside of the controller, and any activity will just checks connection, scans, connects, writes command, .... and subscribes `EventBus` events to get notification from device, connection status,... — mudin, Jan 17 '18 at 01:14
One more issue I have is sometimes it is scanning even scanning activity is stopped. what do you think? — mudin, Jan 17 '18 at 01:22
That one (or more) `Subsrcription` to scanning was not unsubscribed — Dariusz Seweryn, Jan 17 '18 at 07:13

RxAndroidBle - How to disconnect all connected devices?

1 Answers1