Question

我以这种方式扩展了MKPointAnnotation类：

class CustomPointAnnotation: MKPointAnnotation{

    let eventID: Int
    let coords: CLLocationCoordinate2D
    var title: String? // error here
    let location:String

    init(eventID:Int, coords:CLLocationCoordinate2D, location:String, title:String?) {

        self.eventID = eventID
        self.coords = coords
        self.title = title
        self.location = location

        super.init()
    }
}

我得到一个错误：

Cannot override with a stored property 'title'

（我想如果将成员coords重命名为coordinate也会遇到相同的错误）。

因此，我尝试了以下操作：

private var _title:String?

override var title: String? {
        get { return _title }
        set { _title = newValue }
    }

但是，当我在self.title = title的正文中添加init时，我得到：

'self' used in property access 'title' before 'super.init' call

如果我将super.init()移到上方，则会出现两种错误：

Property 'self.eventID' not initialized at super.init call (1 error)
Immutable value 'self.coords' may only be initialized once (repeated for every property)

声明title属性的正确方法是什么？是否有可能覆盖它？我发现了许多与此主题有关的问题，但没有扩展内置类的示例。感谢您的帮助

Answer 1

您需要在初始化程序中设置_title，而不是title。由于这是title的私有支持属性，因此，当您首次访问title时，它将具有正确的值，而无需直接设置。

class CustomPointAnnotation: MKPointAnnotation {

    let eventID: Int
    let coords: CLLocationCoordinate2D
    let location:String

    private var _title:String?

    override var title: String? {
        get { return _title }
        set { _title = newValue }
    }

    init(eventID:Int, coords:CLLocationCoordinate2D, location:String, title:String?) {

        self.eventID = eventID
        self.coords = coords
        self._title = title
        self.location = location

        super.init()
    }
}

Answer 2

您为什么需要再次重新声明var title: String?？通过将MKPointAnnotation子类化，您已经可以访问title。（coords也是如此）。

您可以在super.init()

之后设置标题

init(eventID: Int, coords: CLLocationCoordinate2D, location: String, title: String?) {

        self.eventID = eventID
        self.coords = coords
        self.location = location

        super.init()
        self.title = title
    }

如果出于可读性考虑，要将coordiante重命名为coords，建议使用扩展名：

extension CustomPointAnnotation {
    var coords: CLLocationCoordinate2D {
        get { return coordinate }
        set { coordinate = newValue }
    }
}

并像标题一样在super.init()之后分配它。

Answer 3

将注释类设置为

import MapKit


class DGPointAnnotation: NSObject, MKAnnotation {

    var coordinate: CLLocationCoordinate2D
    var title:String?
    var id:Int?
    var sectionId:Int?
    var lat:Double?
    var lng:Double?
    var imageUrl: String?
    var isPartner:Bool?
    var url: String?
    var type:String?
    var subType:Int?


    init(coordinate: CLLocationCoordinate2D) {
        self.coordinate = coordinate
    }
}

在您的视图控制器中，具有MKMapViewDelegate并添加以下代码。

let mapView = MKMapView()
mapView.frame = CGRect(x: 0, y: 0, width: self.view.frame.width, height: 400)
mapView.mapType = MKMapType.standard
self.view.addSubview(mapView)
loadMarkers()



func loadMarkers(){
    if let markers = theMarkersObj{
        for marker in markers{
            let latLimitMIN : Double = -90.00
            let latLimitMAX : Double = 90.00
            let longLimitMIN : Double = -180.00
            let longLimitMAX : Double = 180.00

            let lat = marker.lat ?? 0.0
            let lng = marker.lng ?? 0.0

            let centerLocation = CLLocationCoordinate2DMake(CLLocationDegrees(lat), CLLocationDegrees(lng));
            let mynumLat:Double = Double(lat)
            let mynumLong:Double = Double(lng)

            let point = DGPointAnnotation(coordinate: centerLocation)
            point.id = marker.id
            point.sectionId = marker.sectionId
            point.title = marker.title ?? ""
            let mapSpan = MKCoordinateSpanMake(0.5, 0.5)
            let mapRegion = MKCoordinateRegionMake(centerLocation, mapSpan)
            if (!(mynumLat < latLimitMIN) && !(mynumLat > latLimitMAX) && !(mynumLong < longLimitMIN) && !(mynumLong > longLimitMAX)) {
                self.mapView.setRegion(mapRegion, animated: true);
            }
            self.mapView.addAnnotation(point)
            self.mapView.delegate = self


        }
    }
    //print(myMapView?.annotations.count)
}

用存储的属性覆盖

3 个答案: