Ios Swift MapKit-注释不会显示在地图视图中

我正在尝试使用MapKit framework创建一个MapView，它查找当前用户位置并显示附近的餐馆。但是，当我试图显示注释时，它们不会显示

我尝试打印（response.mapItems）来检查它是否有效，结果很好，因为它打印了控制台中找到的一些餐馆的信息

因此，我不知道为什么这些没有在地图上标注

以下是我编写的代码：

import UIKit
import MapKit
import CoreLocation

class RestaurantViewController: UIViewController, CLLocationManagerDelegate {

@IBOutlet weak var map: MKMapView!

let manager = CLLocationManager()

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

    let location = locations[0]

    let span:MKCoordinateSpan = MKCoordinateSpanMake(0.025, 0.025)
    let myLocation:CLLocationCoordinate2D = CLLocationCoordinate2DMake(location.coordinate.latitude, location.coordinate.longitude)
    let region:MKCoordinateRegion = MKCoordinateRegionMake(myLocation, span)

    map.setRegion(region, animated: true)

    self.map.showsUserLocation = true
}

override func viewDidLoad() {
    super.viewDidLoad()

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

    let request = MKLocalSearchRequest()
    request.naturalLanguageQuery = "restaurant"

    request.region = map.region

    let search = MKLocalSearch(request: request)
    search.start { (response, error) in

        guard let response = response else {
            return
        }

        for item in response.mapItems {
            print(response.mapItems) - Console shows some restaunrant outputs that were correctly fetched
            let annotation = MKPointAnnotation()
            annotation.coordinate = item.placemark.coordinate
            annotation.title = item.name

            DispatchQueue.main.async {
                self.map.addAnnotation(annotation)
            }

        }

    }
}

}

---

实现viewForAnnotation

   func mapView(_ mapView: MKMapView,viewFor annotation: MKAnnotation) -> MKAnnotationView?

---

在这里查看我的演示

如果您的注释实现有点不成功，请允许我解释一下应该如何实现

向地图添加注释依赖于两件事

符合

MKAnnotation

的类

MKAnnotationView

的子类

您的地图添加了注释，但它不知道如何显示注释，因此什么也不显示。您可以通过实现

viewForAnimation

告诉它如何显示它们。请看我下面的示例：

class PinAnnotation: NSObject, MKAnnotation {

    var coordinate: CLLocationCoordinate2D

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

class PinAnnotationView: MKAnnotationView {

    @available(*, unavailable)
    override init(annotation: MKAnnotation?, reuseIdentifier: String?) {
        super.init(annotation: annotation, reuseIdentifier: reuseIdentifier)
    }

    @available(*, unavailable)
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }

    init(annotation: PinAnnotation) {
        super.init(annotation: annotation, reuseIdentifier: nil)

        self.frame = CGRect(x: 0, y: 0, width: 30, height: 30)

        self.image = UIImage(named: "mypinimage") // or whatever.
    }
}

这里我们有我上面提到的两个对象的定义

func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
        if let imageAnnotation = annotation as? ImageAnnotation {
            let view = ImageAnnotationView(annotation: imageAnnotation)
            return view
        }

        return nil
    }

---

这里是我上面提到的

viewForAnnotation

的实现。

我想问一下它到底是如何工作的，因为我不知道该怎么做。response.mapItems和用户位置之间的距离是分开的吗？

func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
        if let imageAnnotation = annotation as? ImageAnnotation {
            let view = ImageAnnotationView(annotation: imageAnnotation)
            return view
        }

        return nil
    }