Loosing reference to state when listening to characteristics

Issue

So I've tried multiple solutions to store states but for some reason I can't figure out why I'm loosing the (latest) state of some context. I'm using the following function to get an update on a specific characteristic (I also tried the .monitor() directly on the characteristic).

// This is in the BluetoothProvider
device.monitorCharacteristicForService(
    service.uuid,
    characteristic.uuid,
    onUpdate)

Further I have a function to check the state:

// This is in the BluetoothProvider
const updating = () => {
    if (currentMatch != null && currentPerson != null) {
        console.log('found person')
    } else {
        console.log('no person')
    }
}

The properties are stored in a reducer with an API/Data MatchProvider provider:

const { currentMatch, currentPerson } = useContext(MatchDataContext)

The onUpdate function:

const onUpdate = (
    error: BleError | null,
    characteristic: Characteristic | null
) => {
    updating()
}

The provider is in the the correct place:

<MatchProvider>
    <BluetoothProvider>
      <Routes>
      </Routes>
    </BluetoothProvider>
  </MatchProvider>

I've tried moving it to another component/provider/redux it doesn't matter. The onUpdate function just can't get the correct state. The UI works perfectly and the state is stored but the onUpdate method never gets the value.

Solution

Eventually I found the fix, what I did was add the following to the BluetoothProvider

const matchRef = useRef(currentMatch);
const personRef = useRef(currentPerson);

React.useEffect(() => {
    matchRef.current = currentMatch
    personRef.current = currentPerson
}, [currentMatch, currentPerson]);

This allowed me to listen to the updates from the MatchDataContext and store the references. Because down the file I had a subscription that was triggered when the bluetooth device received a new message, and this wasn't up-to-date on the latest state.

const onUpdate = (
    error: BleError | null,
    characteristic: Characteristic | null
) => {
    if (matchRef.current != null && personRef.current != null) {
        console.log('using match', JSON.stringify(matchRef.current, null, 2))
    }
}

For some reason all debugging tools indicated that the value was there, in the BluetoothProvider but when I called the property it was null.

Answered By - Leon