由于 Swift 不断更新它的 API 规范并且在它的弃用中不够优雅，答案中存在一些严重的不一致......所以我决定在这里问这个问题。

我当前的代码说明了通过异步函数更新注释，该函数从互联网上下载图像作为远程 URL。它可以获取 data 数据类型的 UIImage 没问题。但是，我不太明白发生了什么，也不太明白为什么我们需要以这种方式出列和设计解决方案。

问题是，为什么我们需要以这种方式设计我们的注释，而我们只需将注释 View 转换为注释而不用担心每次更新？

请查看以下代码并启发我:

import Foundation
import UIKit
import MapKit
import CoreLocation

class MapView: UIViewController, MKMapViewDelegate, CLLocationManagerDelegate {

    var locationManager:CLLocationManager!
    var firstCenter = false

    var regionRadius: CLLocationDistance = 1000
    var mapView: MKMapView!
    var av:MKPinAnnotationView!

    override func viewDidLoad() {
        super.viewDidLoad()

        view.backgroundColor = UIColor.white

        mapView = MKMapView(
            frame:
            CGRect(
                x: 0,
                y: 0,
                width: view.frame.width,
                height: view.frame.height
            )
        )

        mapView.mapType = MKMapType.standard
        mapView.isZoomEnabled = true
        mapView.isScrollEnabled = true
        mapView.delegate = self

        view.addSubview(mapView)

        mapView.center = view.center

        locationManager = CLLocationManager()
        locationManager.delegate = self
        locationManager.requestAlwaysAuthorization()
        locationManager.requestWhenInUseAuthorization()

        if  CLLocationManager.locationServicesEnabled() {
            print("Looking for locations")
            locationManager.desiredAccuracy = kCLLocationAccuracyBest
            locationManager.startUpdatingLocation()
        }
    }

    public func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
        let userLocation = locations[0]

        if firstCenter == false {
            centerMapOnLocation(location: userLocation)
            firstCenter = true

            let location2d = CLLocationCoordinate2D(latitude: userLocation.coordinate.latitude, longitude: userLocation.coordinate.longitude)

            let url = URL(string: "https://graph.facebook.com/" + FB.id + "/picture?width=50&height=50")

            DispatchQueue.global().async {
                let data = try? Data(contentsOf: url!)
                DispatchQueue.main.async {
                    let image = UIImage(data: data!)

                    let a = PinAnnotation()
                    a.title = "Netflix and Chill"
                    a.coordinate = location2d
                    a.image = image

                    self.mapView.addAnnotation(a)
                    self.mapView.showAnnotations(self.mapView.annotations, animated: true)
                }
            }
        }
    }

    public func locationManager(_ manager: CLLocationManager, didFailWithError error: Error) {
        print("Error \(error)")
    }

    public func centerMapOnLocation(location: CLLocation) {
        let coordinateRegion = MKCoordinateRegionMakeWithDistance(location.coordinate,regionRadius * 2.0, regionRadius * 2.0)

        mapView.setRegion(coordinateRegion, animated: true)
    }

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

        var annotationView = mapView.dequeueReusableAnnotationView(withIdentifier: "pin")

        if annotationView != nil {
            annotationView?.annotation = annotation
        } else {
            annotationView = MKAnnotationView(
                annotation: annotation,
                reuseIdentifier: "pin"
            )
        }

        annotationView?.cornerRadius = 25

        let anno = annotation as? PinAnnotation
        annotationView?.image = anno?.image

        return annotationView
    }

}

class PinAnnotation: MKPointAnnotation {
    var image:UIImage!
}

谢谢你的时间，克里斯

最佳答案

他们之所以这样设计是出于性能方面的考虑。这是他们官方文档的直接引用。

“出于性能原因，您通常应该在 map View 中重用 MKAnnotationView 对象。随着注释 View 移出屏幕， map View 将它们移动到内部管理的重用队列。随着新注释移到屏幕上，您的代码会提示提供相应的注释 View ，您应该始终尝试在创建新 View 之前将现有 View 出列。在性能关键操作(例如滚动)期间，出列可以节省时间和内存。”

关于ios - Swift 3 - 理解 MKAnnotationView 和 mapView() 函数，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/41027322/