MKPlacemark上的参数类型错误

Question

我试图用MKMapItem编写一个函数，但是我得到了一个字符串错误。以下是代码：

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
}

当我试图创建placemark时，我得到了以下错误：

无法转换"String : String?“类型的值？参数类型"String : AnyObject？

完整的类代码：

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]

"func mapItem() -> MKMapItem { }“的完整代码是：

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subtitle属性看起来像一个可选字符串，但是MKPlacemark初始化程序需要一个类型为[String : AnyObject]?的addressDictionary参数。

那是什么意思？

预期的参数类型是一个字典，其中键是String，值是AnyObject类型，所以它可以是任何东西。任何东西除了零值！但是您的subtitle属性可以是零，因此您有此错误。

在使用之前，打开您的值：

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MKMapItem为零，也可以返回一个可选的subtitle对象。这是你的选择;)