當我將其添加到我的應用程序的viewDidLoad中時，我的annonation不可見

Question

我正在開發一個應用程序，用戶必須在地圖上標記位置，然後保存它。然後，我的應用程序將其歸檔，當用戶想要查看該位置時，該應用程序應該檢索該位置的座標，並在存在座標時在地圖上添加一個annonation。下面是我創建的顯示信息的用戶selected-

@IBOutlet var mapGestureRecognizer: UIGestureRecognizer! 
var item: itemData? 

// Item Outlets 
@IBOutlet weak var itemInfoView: UIView! 
@IBOutlet weak var itemNameTextField: UITextField! 
@IBOutlet weak var itemDescriptionLabel: UITextView! 
@IBOutlet weak var mapView: MKMapView! 

// Item Location Outlets 
@IBOutlet weak var itemLocationView: UIView! 
@IBOutlet weak var itemLocationTextView: UITextView! 

let dropPin = MKPointAnnotation() 

override func viewDidLoad() { 
    super.viewDidLoad() 

    self.mapView.delegate = self 

    // Data loading 
    itemNameTextField.delegate = self 
    itemDescriptionLabel.delegate = self 
    itemLocationTextView.delegate = self 

    // Press recognizer 

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

     let annotationView = MKAnnotationView(annotation: annotation, reuseIdentifier: "myAnnotationView") 
     // configure the view 

     return annotationView 
    } 

    if let item = item { 

     itemNameTextField.text = item.itemName 
     itemDescriptionLabel.text = item.itemDescription 
     itemLocationTextView.text = item.itemPlace 

     dropPin.coordinate = mapView.convert(item.mapPoint, toCoordinateFrom: mapView) 
     dropPin.title = "Location of \(item.itemName)" 
     mapView.addAnnotation(dropPin) 
     print("Set the location of item pin to \(String(describing: dropPin.coordinate))") 


    } 

    // Styles 
    itemInfoView.layer.cornerRadius = 3 
    itemInfoView.layer.shadowColor = UIColor(red:0/255.0, green:0/255.0, blue:0/255.0, alpha: 1.0).cgColor 
    itemInfoView.layer.shadowOffset = CGSize(width: 0, height: 1.75) 
    itemInfoView.layer.shadowRadius = 1.7 
    itemInfoView.layer.shadowOpacity = 0.45 

    itemLocationView.layer.cornerRadius = 3 
    itemLocationView.layer.shadowColor = UIColor(red:0/255.0, green:0/255.0, blue:0/255.0, alpha: 1.0).cgColor 
    itemLocationView.layer.shadowOffset = CGSize(width: 0, height: 1.75) 
    itemLocationView.layer.shadowRadius = 1.7 
    itemLocationView.layer.shadowOpacity = 0.45 

    } 

override func didReceiveMemoryWarning() { 
    super.didReceiveMemoryWarning() 

} 
let annotation = MKPointAnnotation() 
//let point = mapView.convert(coordinate, toPointTo: overlayView) 
func action(gestureRecognizer:UIGestureRecognizer){ 

    if let item = item { 
     dropPin.coordinate = mapView.convert((item.mapPoint), toCoordinateFrom: mapView) 
     dropPin.title = "Location of \(item.itemName)" 
     mapView.addAnnotation(dropPin) 
     print("Set the location of item pin to \(String(describing: dropPin.coordinate))") 
    } 

    else { 
     let itemName = itemNameTextField.text 
     let touchPoint = gestureRecognizer.location(in: mapView) 
     let newCoordinates = mapView.convert(touchPoint, toCoordinateFrom: mapView) 
     annotation.coordinate = newCoordinates 
     annotation.title = "Location of \(itemName!)" 
     mapView.addAnnotation(annotation) 
    } 

} 

@IBAction func mapLocationPress(_ sender: UILongPressGestureRecognizer) { 
     action(gestureRecognizer: mapGestureRecognizer) 

} 

所有打印我創建工作報表一段代碼，讓我知道，應用程序確實保存座標，它是否正確轉換它們。但是，當應用程序加載viewDidLoad的if let item = item部分中的信息時，該引腳不會像它應該放在地圖上一樣。

有沒有人看到我的代碼爲什麼沒有按照它應該的方式工作？謝謝！

如果你需要我的完整代碼，告訴我，我會把它放到我的問題。

Answer 1

您需要使用

func mapView(mapView: MKMapView, viewForAnnotation annotation: MKAnnotation) -> MKAnnotationView? { 
     let annotationView = MKAnnotationView(annotation: annotation, reuseIdentifier: "myAnnotationView") 
     // configure the view 

     return annotationView 
} 

您viewDidLoad()功能

外

Answer 2

你應該把mapViewFunc出viewDidLoad，但如果你想將它留在viewDidLoad

嘗試

func viewDidLoad() { 
    super.viewDidLoad() 
    DispatchQueue.main.async { 
     // add pin 
    } 
}