Question

根据this post，只要您拨打addAnnotation方法，就会调用mapView:viewForAnnotation

但是，以下代码只调用mapView:viewForAnnotation一次。我有几个注释，但＆＃34;视图称为＆＃34;只印了一次。我想这与线程有关吗？

import UIKit
import MapKit
import CoreLocation

class ViewController: UIViewController, UITextFieldDelegate, MKMapViewDelegate, CLLocationManagerDelegate {

    @IBOutlet var searchtext: UITextField!
    @IBOutlet var map: MKMapView!

    var locationManager = CLLocationManager()

    override func viewDidLoad() {
        super.viewDidLoad()

        self.searchtext.delegate = self

        locationManager.delegate = self
        self.map.delegate = self

        locationManager.desiredAccuracy = kCLLocationAccuracyBest
        locationManager.requestWhenInUseAuthorization()
        locationManager.startUpdatingLocation()
    }

    func textFieldDidBeginEditing(textField: UITextField!) {    //delegate method
        var allAnnotations = self.map.annotations
        self.map.removeAnnotations(allAnnotations)
    }

    func textFieldShouldReturn(textField: UITextField!) ->Bool {
        textField.resignFirstResponder()

        //...

        let session = NSURLSession.sharedSession()

        var task = session.dataTaskWithURL(url!, completionHandler: { (date, response, error) -> Void in
            if (error != nil) {
                println(error)
            }else {
                var placenum = 0
                //placenum is to see if all the places are in the visible rect. If so I will use showAnnotations to zoom (in) to the best-fitted view show them. If not, I will only show these in the visible rect
                for place in places {
                    //...
                    if (regionContains(self.map.region, coordinate)) {
                        placenum = placenum+1
                    }
                    self.map.addAnnotation(annotation)
                }

                if (placenum==places.count) {
                    self.map.showAnnotations(self.map.annotations, animated: true)
                }
            }

        })

        task.resume()

        return true
    }

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

        //...
        self.map.setRegion(region, animated: false)

        locationManager.stopUpdatingLocation()
    }

    func mapView(mapView: MKMapView!, viewForAnnotation annotation: MKAnnotation!) -> MKAnnotationView! {
        println("view called")

        return nil
    }

Answer 1

另外请确保将mapview的委托属性设置为self。

mapview.delegate = self

您也可以使用Connection Inspector（Interface Builder）将mapview的委托出口连接到ViewController

Answer 2

简而言之，当注释落在地图视图的可见部分内时，会调用viewForAnnotation。也就是说，（a）注释已添加到地图视图中，它随region或（b）region更改而下降，以便之前未显示的注释是。

顺便说一下，completionHandler的{{1}}将不在主线程上。必须将任何UI更新显式分派回主线程，例如

dataTaskWithURL

我建议确保在主线程上发生与地图视图的交互，如上所示。

顺便提一下，请记住，如果您在地图上显示用户位置，那么本身会导致dispatch_async(dispatch_get_main_queue()) { for place in places { //... placenum = placenum + 1 self.map.addAnnotation(annotation) } self.map.showAnnotations(self.map.annotations, animated: true) }被调用。因此，如果您只看到一次调用，则可能需要确认viewForAnnotation是annotation还是您添加的其中一个注释。

什么时候在Swift中调用mapView：viewForAnnotation？

2 个答案: