swift - 当我离开应用程序时，如何保存我的 MapView 注释？

Question

func addPin(_ sender: UILongPressGestureRecognizer) {

    let location = sender.location(in: self.mapView)
    let locCoord = self.mapView.convert(location, toCoordinateFrom: self.mapView)

    let annotation = MKPointAnnotation()

    annotation.coordinate = locCoord
    annotation.title = titleTextField.text

    self.mapView.addAnnotation(annotation)

    print("This will become the annotation title: \(titleTextField.text).")
    print(annotation.coordinate.latitude, annotation.coordinate.longitude)

}

我是 swift 新手，想知道如何在离开应用程序后保存我的注释。另外，如果用户没有拿起手指，如何阻止形成多个注释？

Answer 1

您可能需要做的是将 MKPointAnnotation 存储为 UserDefaults 中的 Data。为此，您将根据所有 mapView 的注释创建一个字典数组:

func addPin(_ sender: UILongPressGestureRecognizer) {

    let location = sender.location(in: self.mapView)
    let locCoord = self.mapView.convert(location, toCoordinateFrom: self.mapView)

    let annotation = MKPointAnnotation()

    annotation.coordinate = locCoord
    annotation.title = titleTextField.text

    self.mapView.addAnnotation(annotation)

    //Create a dictionary from the annotation
    let newAnnotationDict = [
        "lat": locCoord.latitude
        "lng": locCoord.longitude
        "title": annotation.title
    ]

    //Pull the stored annotations data
    var annotationsArray: [[String:Any]]!
    var annotationsData = UserDefaults.standard.data(forKey: "StoredAnnotations")

    //If the data is nil, then set the new annotation as the only element in the array
    if annotationsData == nil {
        annotationsArray = [newAnnotationDict]
    } else {
        //If it isn't nil, then convert the data into an array of dicts
        do {
            //Convert this data into an array of dicts
            annotationsArray = try JSONSerialization.jsonObject(with: annotationsData, options: []) as! [[String:Any]]
            annotationsArray.append(newAnnotationDict)
        } catch {
            print(error.localizedDescription)
        }

    }

    do {

        //Use JSONSerialization to convert the annotationsArray into Data
        let jsonData = try JSONSerialization.data(withJSONObject: annotationsArray, options: .prettyPrinted)

        //Store this data in UserDefaults
        UserDefaults.standard.set(jsonData, forKey: "StoredAnnotations")
    } catch {
        print(error.localizedDescription)
    }

    print("This will become the annotation title: \(titleTextField.text).")
    print(annotation.coordinate.latitude, annotation.coordinate.longitude)

}

然后，当再次打开 View Controller 时，您需要从 UserDefaults 中提取此 Data 并将其解析为 MKPointAnnotation< 的数组 对象。

class MapViewController: UIViewController {

    //Whenever the view loads, check if there were any annotations stored last time
    override func viewDidLoad() {
        super.viewDidLoad()

        //Check if the data for "StoredAnnotations" exists
        if UserDefaults.standard.data(forKey: "StoredAnnotations") != nil {

            var storedAnnotationObjects = [MKPointAnnotation]()

            do {

                //Get the data from UserDefaults
                let storedAnnotationsData = UserDefaults.standard.data(forKey: "StoredAnnotations")!

                //Convert this data into an array of dictionaries
                let storedAnnotationsArray = try JSONSerialization.jsonObject(with: storedAnnotationsData, options: []) as! [[String:Any]]

                for dict in storedAnnotationsArray {
                    //Initialize a new annotation and set the annotation's properties
                    let newAnnotation = MKPointAnnotation()
                    newAnnotation.coordinate = CLLocationCoordinate2D(latitude: dict["lat"] as! CGFloat, longitude: dict["lng"] as! CGFloat)
                    newAnnotation.title = dict["title"] as! String
                    newAnnotationObjects.append(newAnnotation)
                }

                //Add the annotation to the mapView
                self.mapView.annotations = storedAnnotationObjects
            } catch {
                print(error.localizedDescription)
            }
        }
    }

    ...

}

如果注释被删除，您需要将存储的数据类似地转换为字典数组，并删除适当的对象并更新数据。