void MapRegionChanged(object sender, MKMapViewChangeEventArgs e)
{
Dictionary <string, AirportAnnotation> current = new Dictionary <string, AirportAnnotation> ();
List <AirportAnnotation> added = new List <AirportAnnotation> ();
// Query for the list of airports in the new region
foreach (var airport in Airports.GetAirports(mapView.Region))
{
AirportAnnotation aa;
if (annotations.ContainsKey(airport.FAA))
{
// This airport is already in view...
aa = annotations[airport.FAA];
annotations.Remove(airport.FAA);
}
else
{
// This is a new annotation, keep track of it in 'added'
aa = new AirportAnnotation(airport);
added.Add(aa);
}
current.Add(aa.Airport.FAA, aa);
}
if (annotations.Count > 0)
{
// Remove annotations that are no longer in view
mapView.RemoveAnnotations(annotations.Values.ToArray());
annotations.Clear();
}
if (added.Count > 0)
{
mapView.AddAnnotation(added.ToArray());
added.Clear();
}
annotations = current;
}
IEnumerable <Airport> GetAirports(MKCoordinateRegion region)
{
if (visited)
{
foreach (var code in LogBook.GetVisitedAirports())
{
Airport airport = Airports.GetAirport(code, AirportCode.FAA);
if (airport != null)
{
yield return(airport);
}
}
}
else
{
foreach (var airport in Airports.GetAirports(region))
{
yield return(airport);
}
}
yield break;
}