swift - 为什么我在应用程序标签上的地标前收到 "optional"字样？

Question

编辑:自请求以来，现在已发布完整代码。

为什么我在应用标签上的地标前会看到“可选”一词？

我最初像这样\(p.thoroughfare!) 展开了每个属性，并且它起作用了，但只有当有是 subThoroughfare 时。我无法解包 \(subThoroughfare) 因为我不知道在哪里做，因此当 没有 subThoroughfare 时应用程序崩溃了。

    import UIKit
    import CoreLocation

    class ViewController: UIViewController, CLLocationManagerDelegate {

var manager:CLLocationManager!


@IBOutlet var latitudeLabel: UILabel!
@IBOutlet var longitudeLabel: UILabel!
@IBOutlet var courseLabel: UILabel!
@IBOutlet var speedLabel: UILabel!
@IBOutlet var altitudeLabel: UILabel!
@IBOutlet var addressLabel: UILabel!

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.

    manager = CLLocationManager()
    manager.delegate = self
    manager.desiredAccuracy - kCLLocationAccuracyBest
    manager.requestWhenInUseAuthorization()
    manager.startUpdatingLocation()


}

//NOTE: [AnyObject] changed to [CLLocation]

func locationManager(manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {

    print(locations)

    //userLocation - there is no need for casting, because we are now using CLLocation object

    var userLocation:CLLocation = locations[0]

    self.latitudeLabel.text = "\(userLocation.coordinate.latitude)"

    self.longitudeLabel.text = "\(userLocation.coordinate.longitude)"

    self.courseLabel.text = "\(userLocation.course)"

    self.speedLabel.text = "\(userLocation.speed)"

    self.altitudeLabel.text = "\(userLocation.altitude)"

    CLGeocoder().reverseGeocodeLocation(userLocation, completionHandler: { (placemarks, error) -> Void in

        if (error != nil) {

            print(error)

        } else {

            if let p = placemarks?[0] {

                var subThoroughfare : String = ""

                if (p.subThoroughfare != nil) {

                    subThoroughfare = p.subThoroughfare!

                }

                self.addressLabel.text = "\(subThoroughfare) \(p.thoroughfare) \n \(p.subLocality) \n \(p.subAdministrativeArea) \n \(p.postalCode) \n \(p.country)"

            }


        }

    })

Answer 1

你得到了 Optional("string") 因为你没有解包这些可选变量。

如果 var str:String? 为 nil 并且您设置了 myLabel.text = str，您的标签文本将为空!如果它有一个值，比如说 str = "yaw!" 并且您设置了 myLabel.text = str，标签将显示 yaw!/p>

现在，如果您的字符串是 nil 并且您使用字符串插值 myLabel.text =\(str)，您的标签文本将显示 nil .如果您设置 str = "yaw!" 和 myLabel.text =\(str)，标签将显示 Optional("yaw!")

要解决您的问题，您必须以安全的方式解包您的变量:

创建一个 var 来保存完整的字符串，然后将非 nil 值添加到该字符串。

    var fullString:String = ""
    if let _ = p.subThoroughfare { fullString += "\(p.subThoroughfare!)" } // Check if the attribute is not nil before adding it to the string

将第 2 行复制到每个属性 p.thoroughfare、p.subLocality 等

最后，设置 self.addressLabel.text = fullString