在展开可选值时意外发现 MKMapView 为 nil

Question

我编写了这个函数来在地图上绘制叠加层，当我在 MapViewController 的 viewDidLoad 中调用它时它工作正常。

func drawTripLocations(locs: Array<Location>){
  var loclist: Array<CLLocationCoordinate2D> = []
             if (locs.count > 3){
                    for loc in locs{
                        if (loc.gps == 1){
                            let cord = CLLocationCoordinate2D(latitude: loc.lat!, longitude: loc.lon!)
                            loclist.append(cord)
                }
            }
        }

          if(loclist != nil && loclist.count > 1){

        /*   if let overlays = self.mainMapView?.overlays {
         self.mainMapView.removeOverlays(overlays)
         self.mainMapView.delegate = self
         }
         if let annotations = self.mainMapView?.annotations {
         self.mainMapView.removeAnnotations(annotations)
         self.mainMapView.delegate = self
         }*/

        let startmark = loclist.first
        let endmark = loclist.last


        let polyline = MKPolyline(coordinates: loclist, count: loclist.count)
            print(polyline.pointCount)
        let mapAnnotation = MKPointAnnotation();

        self.addDefaultMapPin("Start" , coordinates: startmark!)
        self.addDefaultMapPin("end" , coordinates: endmark!)

        self.mainMapView.add(polyline)
        zoomPolyline(polyline)

    }

}

我需要使用此函数根据 TableViewController 中的新位置绘制叠加层，因为我已在此视图控制器中编写了一个函数：

    func getPathLocations(loclist: Array<Location>, stloc: Location, endloc: Location){

    var locations: Array<Location> = []

    if loclist != nil && loclist.count > 1{
        for loc in loclist{
            if((Double(loc.tm!) > Double(stloc.tm!) && loc.ign) && (Double(loc.tm!) <= Double(endloc.tm!)) ){
                locations.append(loc)
            }
        }
    }
    print(locations.count)

    let mainstoryboard: UIStoryboard = UIStoryboard.init(name: "Main", bundle: nil)
            let mapViewController: MapViewController = mainstoryboard.instantiateViewController(withIdentifier: "MapViewController") as! MapViewController

        mapViewController.drawTripLocations(locs: locations)
}

我面临的问题是当我从其他 viewController.

调用此函数时，drawTripLocations() 中的 mainMapView 对象始终为 nil

Answer 1

是的，因为 MapViewController 视图尚未加载并且 mainMapView 是 nil。当您按下/呈现视图控制器时，将加载视图。

选项 1

通过访问 view 属性来加载视图 UIViewController

let mainstoryboard = UIStoryboard.init(name: "Main", bundle: nil)
let mapViewController = mainstoryboard.instantiateViewController(withIdentifier: "MapViewController") as! MapViewController
_ = mapViewController.view // this will make sure view is loaded
mapViewController.drawTripLocations(locs: locations)

选项 2（更好的一个）

在你的MapViewController中添加一个属性

var locations:Array<Location>?

并在呈现/推送之前设置位置（而不是调用 drawTripLocations）MapViewController。

let mainstoryboard = UIStoryboard.init(name: "Main", bundle: nil)
let mapViewController = mainstoryboard.instantiateViewController(withIdentifier: "MapViewController") as! MapViewController
mapViewController.locations = locations

并且在 MapViewController

的 viewDidLoad 方法中

override func viewDidLoad() {
    // other code
    if let locations = locations {
        drawTripLocations(locs: locations)
    }
}

在展开可选值时意外发现 MKMapView 为 nil

MKMapView is unexpectedly found nil while unwrapping an Optional value

mkmapview

swift