NavigationMapView.routeLineTracksTraversal only works inside NavigationViewController

[1ec5]

NavigationMapView.routeLineTracksTraversal is billed as an option to enable the “erasing route line” or “vanishing route line” feature on any NavigationMapView (#1307). But this property only works when the map view is embedded inside a NavigationViewController, because the only thing that reads the property is in RouteMapViewController. Nor does the feature work in CarPlay, which has a CarPlayNavigationViewController instead of a NavigationViewController.

mapbox-navigation-ios/MapboxNavigation/RouteMapViewController.swift

Lines 460 to 462 in aaed03d

	if mapView.routeLineTracksTraversal {
	mapView.fadeRoute(progress.fractionTraveled)
	}

Unusually, NavigationMapView.fadeRoute(_:) is an internal method not exposed publicly, so there’s no workaround for an application that implements its own custom UI for turn-by-turn navigation.

mapbox-navigation-ios/MapboxNavigation/NavigationMapView.swift

Line 603 in aaed03d

func fadeRoute(_ fractionTraveled: Double) {

We should rename fadeRoute(_:) to updateRoute(for:), have it take a RouteProgress instead of a raw number, and expose it publicly. Since routeLineTracksTraversal is dependent on functionality outside of NavigationMapView, namely progress updates, we should either move it to NavigationViewController or move that conditional inside updateRoute(for:). Finally, we should call updateRoute(for:) from within CarPlayNavigationViewController.progressDidChange(_:) too.

/cc @mapbox/navigation-ios @d-prukop @avi-c @captainbarbosa