从 'CLLocation?' 向下转换为 'CLLocation' 只解包可选值；您是要使用“！”吗？

Question

我试图在地图视图上显示用户当前位置，但在位置管理器功能的第一行出现错误

这是我的代码

import UIKit
import MapKit

class FirstViewController: UIViewController, CLLocationManagerDelegate {

@IBOutlet weak var mapkitView: MKMapView!
var locationManager: CLLocationManager!

override func viewDidLoad()
{
    super.viewDidLoad()

    if (CLLocationManager.locationServicesEnabled())
    {
        locationManager = CLLocationManager()
        locationManager.delegate = self
        locationManager.desiredAccuracy = kCLLocationAccuracyBest
        locationManager.requestAlwaysAuthorization()
        locationManager.startUpdatingLocation()
    }
}

func locationManager(manager: CLLocationManager, didUpdateLocations locations: [CLLocation])
{
    let location = locations.last as! CLLocation

    let center = CLLocationCoordinate2DMake(latitude: location.coordinate.latitude, longitude: location.coordinate.longitude)

    let region = MKCoordinateRegion(center: center, span: MKCoordinateSpan(latitudeDelta: 0.01, longitudeDelta: 0.01))

    self.mapkitView.setRegion(region, animated: true)
}
}

我得到的错误是“从 'CLLocation?' 向下转换到 'CLLocation' 只解包选项；你是想使用 '!' 吗？[=13=]

上线让location=locations.lastas！ CLLocation

Answer 1

您正在强制转换 Optional CLLocation 到 CLLocation，这就是为什么 Swift 建议简单地强制展开它：

let location = locations.last!

如果 locations 为空，这个版本（和你的）将会崩溃。

因此，我建议永远不要强行打开任何东西，而是使用 guard：

guard let location = locations.last else {
    return
}

从 'CLLocation?' 向下转换为 'CLLocation' 只解包可选值；您是要使用“！”吗？

Downcast from 'CLLocation?' to 'CLLocation' only unwraps optionals; did you mean to use '!'?

cllocation

ios

swift