Support rendering of the MKOverlay class (#42)

Sources/MKMapView+Rx.swift

@@ -244,7 +244,7 @@ extension Reactive where Base: MKMapView {
         (_ source: O)
         -> Disposable
         where O.E == [A] {
-            return self.annotations(dataSource: RxMapViewReactiveDataSource())(source)
+            return self.annotations(dataSource: RxMapViewReactiveAnnotationDataSource())(source)
     }
 
     public func annotations<
@@ -263,6 +263,32 @@ extension Reactive where Base: MKMapView {
             }
     }
 
+  // MARK: Binding overlay to the Map
+  public func overlays<
+    A: MKOverlay,
+    O: ObservableType>
+    (_ source: O)
+    -> Disposable
+    where O.E == [A] {
+      return self.overlays(dataSource: RxMapViewReactiveOverlayDataSource())(source)
+  }
+
+  public func overlays<
+    DataSource: RxMapViewDataSourceType,
+    O: ObservableType>
+    (dataSource: DataSource)
+    -> (_ source: O)
+    -> Disposable
+    where O.E == [DataSource.Element],
+    DataSource.Element: MKOverlay {
+      return { source in
+        return source
+          .subscribe({ event in
+            dataSource.mapView(self.base, observedEvent: event)
+          })
+      }
+  }
+
     /// Installs delegate as forwarding delegate on `delegate`.
     /// Delegate won't be retained.
     ///

Sources/RxMapViewReactiveDataSource.swift

@@ -11,7 +11,7 @@ import MapKit
 import RxSwift
 import RxCocoa
 
-public class RxMapViewReactiveDataSource<S: MKAnnotation>
+public class RxMapViewReactiveAnnotationDataSource<S: MKAnnotation>
     : RxMapViewDataSourceType {
     public typealias Element = S
 
@@ -29,5 +29,25 @@ public class RxMapViewReactiveDataSource<S: MKAnnotation>
             }
         }.on(observedEvent)
     }
+}
 
+public class RxMapViewReactiveOverlayDataSource<S: MKOverlay>
+: RxMapViewDataSourceType {
+  public typealias Element = S
+
+  var currentOverlay: [S] = []
+
+  public func mapView(_ mapView: MKMapView, observedEvent: Event<[S]>) {
+    Binder(self) { _, newOverlays in
+      DispatchQueue.main.async {
+        let diff = Diff.calculateFrom(
+          previous: self.currentOverlay,
+          next: newOverlays)
+        self.currentOverlay = newOverlays
+        mapView.addOverlays(diff.added)
+        mapView.removeOverlays(diff.removed)
+      }
+      }.on(observedEvent)
+  }
 }
+