Swift 使用 NotificationCenter 在 View Controller 之间传递数据

Question

我正在尝试使用通知将用户输入坐标的数据从一个 VC 传递到另一个 VC。当我运行代码时，它不会在 MapView 上添加注释，所以我有一种预感，我可能没有设置通知以正确发送输入的坐标，但我不确定哪里出错了。

接受坐标输入的类文件:

import UIKit
import CoreLocation

var locations: [Dictionary<String, Any>] = [] // here I initialize my empty array of locations

class OtherVC: UIViewController {

    @IBOutlet weak var latitudeField: UITextField!
    @IBOutlet weak var longitudeField: UITextField!

    @IBOutlet weak var titleTextField: UITextField!
    var coordinates = [CLLocationCoordinate2D]()

    override func viewDidLoad() {
        super.viewDidLoad()
    }




    @IBAction func addToMap(_ sender: Any) {
        let lat = latitudeField.text!
        let long = longitudeField.text!
        let title = titleTextField.text!
        var location: [String: Any] = ["title": title, "latitude": lat, "longitude": long]
        locations.append(location) 
        NotificationCenter.default.post(name: NSNotification.Name("MapViewController.coordinate.updated"), object: locations, userInfo: nil)

    }


} 

接收通知并放置注解的类文件:

import UIKit
import MapKit
class MapViewController: UIViewController, MKMapViewDelegate {


    @IBOutlet weak var mapView: MKMapView!



    override func viewDidLoad() {
        super.viewDidLoad()
        mapView.delegate = self
    }

    func add(notification: NSNotification) {

        let dict = notification.object as! NSDictionary

        // takes the coordinates from the notification and converts such that the map can interpret them
        let momentaryLat = (dict["latitude"] as! NSString).doubleValue
        let momentaryLong = (dict["longitude"] as! NSString).doubleValue
        let annotation = MKPointAnnotation()
        annotation.title = dict["title"] as? String
        annotation.coordinate = CLLocationCoordinate2D(latitude: momentaryLat as CLLocationDegrees, longitude: momentaryLong as CLLocationDegrees)
        mapView.addAnnotation(annotation)
        self.mapView.centerCoordinate = annotation.coordinate
    }


    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
        let identifier = "pinAnnotation"
        var annotationView = mapView.dequeueReusableAnnotationView(withIdentifier: identifier) as? MKPinAnnotationView

    if annotationView == nil {
        annotationView = MKPinAnnotationView(annotation: annotation, reuseIdentifier: identifier)
        annotationView?.canShowCallout = true
    }

    annotationView?.annotation = annotation
    return annotationView
    }
} 

Answer 1

它与 Objective-C API 相同，但使用 Swift 的语法。

NSNotificationCenter.defaultCenter().addObserver(
self,
selector: #selector(batteryLevelChanged),
name: UIDeviceBatteryLevelDidChangeNotification,
object: nil)

或者在 Swift 3 中:

NotificationCenter.default.addObserver(
self,
selector: #selector(self.batteryLevelChanged),
name: .UIDeviceBatteryLevelDidChange,
object: nil)

如果您的观察者没有继承自 Objective-C 对象，您必须在您的方法前加上 @objc 才能将其用作选择器。

@objc func batteryLevelChanged(notification: NSNotification){     
//do stuff