MKPlacemark上的参数类型错误

Question

我正试图用swift编写一个创建MKMapItem的函数，但遇到了String错误。这是代码：

func mapItem() -> MKMapItem {
    let addressDictionary = [String(kABPersonAddressStreetKey): subtitle]
    let placemark = MKPlacemark(coordinate: coordinate, addressDictionary: addressDictionary)
    let mapItem = MKMapItem(placemark: placemark)
    mapItem.name = title
    return mapItem
}

我在尝试创建placemark:时出现以下错误

无法将类型为"[String:String？]"的值转换为预期的参数类型"[String:AnyObject]？

全类代码：

class Bar: NSObject, MKAnnotation {
    // MARK: Properties
    let id: Int
    let title: String
    let locationName: String
    let url: String
    let imageUrl: String
    let tags: String
    let coordinate: CLLocationCoordinate2D
    // MARK: Initialisation
    init(id: Int, adress: String, name: String, url: String, tags: String, imageUrl: String, coordinate: CLLocationCoordinate2D) {
        // Affectation des attributs
        self.id = id
        self.title = name
        self.locationName = adress
        self.url = url
        self.imageUrl = imageUrl
        self.tags = tags
        self.coordinate = coordinate
    }
    // MARK: Subtitle
    var subtitle: String {
        return locationName
    }
    // MARK: Helper
    func mapItem() -> MKMapItem {
        var addressDictionary : [String:String]?
        addressDictionary = [String(kABPersonAddressStreetKey): subtitle]
        let placemark = MKPlacemark(coordinate: coordinate, addressDictionary: addressDictionary)
        let mapItem = MKMapItem(placemark: placemark)
        mapItem.name = title
        return mapItem
    }    
}

Answer 1

替换此字符串：

  let title: String?

替换此代码：

 var subtitle: String? {
        return locationName
    }

您需要将字幕转换为AnyObject，如下所示：

let addressDict = [String(kABPersonAddressStreetKey): self.subtitle as! AnyObject]

并且"func-mapItem（）->MKMapItem｛｝"的完整代码将是：

func mapItem() -> MKMapItem {
    let addressDict = [String(kABPersonAddressStreetKey): self.subtitle as! AnyObject]
    let placemark = MKPlacemark(coordinate: self.coordinate, addressDictionary: addressDict)
    let mapItem = MKMapItem(placemark: placemark)
    mapItem.name = self.title
    return mapItem
  }

Answer 2

您的副标题属性看起来像一个可选的String，但MKPlacemark初始值设定项需要addressDictionary的类型为[String : AnyObject]?的参数。

这是什么意思？

所需的参数类型是一个字典，其中键为String，值为AnyObject，因此它可以是任何类型。除了零值以外的任何值！但是您的subtitle属性可能为零，因此会出现此错误。

在使用之前先解开你的价值：

func mapItem() -> MKMapItem {
    var addressDictionary : [String:String]?
    if let subtitle = subtitle {
        // The subtitle value used here is a String,
        // so addressDictionary conforms to its [String:String] type
        addressDictionary = [String(kABPersonAddressStreetKey): subtitle
    }
    let placemark = MKPlacemark(coordinate: coordinate, addressDictionary: addressDictionary)
    let mapItem = MKMapItem(placemark: placemark)
    mapItem.name = title
    return mapItem
}

如果subtitle为零，也可以返回可选的MKMapItem对象。选择权在你；）