Swift 2 MKMapViewDelegate rendererForOverlay选项

在 Swift 1.2中我有这个：

class UVC: NSViewController,MKMapViewDelegate {
    // ...

    // **************************************
    // MARK: MapView Delegate
    // **************************************
    func mapView(mapView: MKMapView,rendererForOverlay overlay: MKOverlay) -> MKOverlayRenderer! {
        if overlay is OSGBTiles {
            return OSGBTilesRenderer(tileOverlay: overlay as! OSGBTiles)
        } else if overlay is ESRI {
            return ESRIRenderer(shapeFileOverlay: overlay as! ESRI)
        } else if overlay is MKTileOverlay {
            return MKTileOverlayRenderer(overlay: overlay)
        } else {
            print("UnkNown overlay")
        }
        return nil
    }
}

Swift 2已将mapView：rendererForOverlay的定义更改为现在返回MKOverlayRenderer而不是MKOverlayRenderer！,现在不允许我返回nil(不出所料)因为MKOverlayRenderer不是NilLiteralConvertible.但是,文档(在Xcode 7中)仍然说：

Return Value

The renderer to use when presenting the specified overlay
on the map. If you return nil,no content is drawn for the specified
overlay object.

如果通过我不认识的叠加层,我应该返回什么？

解决方法

根据最新的MKMapView.h,新的函数声明现在是：

// Current renderer for overlay; returns nil if the overlay is not shown.
@available(iOS 7.0,*)
func rendererForOverlay(overlay: MKOverlay) -> MKOverlayRenderer?