[MS-923] Adding internal counter for the amount of loaded candidates in the MatchViewModel

[alexandr-simprints]

Issue description

The MatchViewModel observes the LoadingCandidates event from the Matcher UseCase and emits it to the LiveData's Observer. The LoadingCandidates event that might be emitted multiple times a second.

We've observed that the UI layer processed less than 5% of the events sent to the LiveData:

• 43819 events emitted by the Use Case
• 43819 events forwarded to the LiveData by the ViewModel (0% loss)
• 2372 - received by the observer (MatchFragment, >90% loss)

Not only the events were being lost, the Observer stopped receiving them after some arbitrary threshold - after ~20 events on some devices, ~4000 events on others.

Fix

It was identified that by removing the state reference to itself for update, the issue disappears.

MatcherUseCase.MatcherState.CandidateLoaded -> {
    (_matchState.value as? MatchState.LoadingCandidates)?.let { currentState ->
        _matchState.postValue(currentState.copy(loaded = currentState.loaded + 1)) // changing this line
    }
}

was changed to

MatcherUseCase.MatcherState.CandidateLoaded -> {
    (_matchState.value as? MatchState.LoadingCandidates)?.let { currentState ->
        candidatesLoaded++
        _matchState.postValue(currentState.copy(loaded = candidatesLoaded))
    }
}

This way the new state does need to access old state for update, and no longer exhausts resources to send updates to the LiveData observer.

• CoSync works ✅
• SID local database works ✅

Video before the update:

callback-issue.mp4

Video after the update:

Local database

flow-counter.mp4

CoSync

cosync-counter-id.mp4

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud