Adding support for sharing multiple instances of MapboxNavigationObserver

[kmadsen]

Description

We're going to use MapboxNavigationApp.registerObserver to share subscriptions between different architectures. For example, android auto will register a MapboxNavigationObserver that may also be registered by drop in ui.

This pull request is adding safe ways to get and register MapboxNavigationObserver instances. Note that thread safety is not yet being address in this pull request.

Code samples

Register from multiple paths

Android Auto Session onCreate
and a Fragment onCreate

object AudioGuidanceObserver : MapboxNavigationObserver
if (MapboxNavigationApp.getObservers(MyObserver::class).isEmpty()) {
  MapboxNavigationApp.registerObserver(MyObserver)
}

This will ensure that only one MyObserver is registered. The unregister is tied to the MapboxNavigationApp.lifecycleOwner; meaning that when there are no lifecycles attached the MyObserver instance will be detached but still registered.

Sharing multiple subscriptions

The current MapboxNavigationApp.getObserver will crash when the observer is not found. There are implementations that we should support in case there are multiple/optional observers registered. For example, you may have registered multiple observers that are updating status on a map (nearby places while navigating for example).

MyFragment

// Periodically update the the waiting line size of ev charging stations
class EvStationObserver : MapboxNavigationObserver
val evStations = MapboxNavigationApp.getObservers(EvStationObserver::class)
evStations.forEach {
  // update map marker
}

// Clear all the instances of a specific observer type

class NearbyGasStationObserver : MapboxNavigationObserver
val evStations = MapboxNavigationApp.getObservers(NearbyGasStationObserver::class)
evStations.forEach {
  MapboxNavigationApp.unregister(evStations)
}

[codecov]

Codecov Report

Merging #5829 (9b5f7d3) into main (8472f8a) will increase coverage by 0.00%.
The diff coverage is 90.00%.

@@            Coverage Diff            @@
##               main    #5829   +/-   ##
=========================================
  Coverage     67.66%   67.67%           
- Complexity     3829     3835    +6     
=========================================
  Files           586      586           
  Lines         23572    23577    +5     
  Branches       2714     2716    +2     
=========================================
+ Hits          15951    15955    +4     
- Misses         6603     6604    +1     
  Partials       1018     1018           

Impacted Files	Coverage Δ
...x/navigation/core/lifecycle/MapboxNavigationApp.kt	0.00% <0.00%> (ø)
...tion/core/lifecycle/MapboxNavigationAppDelegate.kt	91.89% <100.00%> (+0.46%)	⬆️
...navigation/core/lifecycle/MapboxNavigationOwner.kt	89.74% <100.00%> (+0.55%)	⬆️

[kmadsen]

Another API i've considered is registering observers with a lifecycle. This would ensure 1 observer exists while a lifecycle is in an active state.

val observer1 = MapboxNavigationApp.register(fragmentLifecycle, State.STARTED, MyObserver::class)
val observer2 = MapboxNavigationApp.register(carSessionLifecycle, State.CREATED, MyObserver::class)
// observer1 == observer2

This is slightly complex to keep track of a multiple maps of Map<Class<extends MapboxNavigationObserver>, Set<Lifecycle>>, where the maps themselves are maintained lifecycle observers. Can be done, takes a bit of testing.

[tomaszrybakiewicz]

LGTM