注释不会在地图上加载

Question

一段时间以来，我一直试图在地图上找到注释的方向。我最近发现了如何做到这一点，但现在并非我的所有注释都会出现在地图上，只有一个注释会出现。我在Cloudkit中使用公共数据库来存储我的所有用户信息。自从我为整个视图控制器提供变量annotation = MKPointAnnotation()以来，我的所有注释都没有在地图上显示。

这就是我获取方向的方式：

let annotation = MKPointAnnotation()

@IBAction func getDirections(_ sender: Any) {
    let view = annotation.coordinate        
    print("Annotation: \(String(describing: view ))")
    let currentLocMapItem = MKMapItem.forCurrentLocation()
    let selectedPlacemark = MKPlacemark(coordinate: view, addressDictionary: nil)
    let selectedMapItem = MKMapItem(placemark: selectedPlacemark)
    let mapItems = [selectedMapItem, currentLocMapItem]
    let launchOptions = [MKLaunchOptionsDirectionsModeKey: MKLaunchOptionsDirectionsModeDriving]
    MKMapItem.openMaps(with: mapItems, launchOptions:launchOptions)
}

这就是我展示我的注释的方式：

func fetch() {
    let truePredicate = NSPredicate(value: true)
    let eventQuery = CKQuery(recordType: "User", predicate: truePredicate)
    let queryOperation = CKQueryOperation(query: eventQuery)
    queryOperation.recordFetchedBlock = { (record : CKRecord!) in

        self.truck.append(record)

        self.annotation.title = record?["username"] as? String
        self.annotation.subtitle = record?["hours"] as? String
        if let location = record?["location"] as? CLLocation {
            self.annotation.coordinate = location.coordinate
        }

        print("recordFetchedBlock: \(record)")

        self.mapView.addAnnotation(self.annotation)
    }

    queryOperation.queryCompletionBlock = { (cursor, error) in

        print("queryCompletionBlock: \(self.truck)")
    }

    database.add(queryOperation)
}

我现在收到这个错误：

This application is modifying the autolayout engine from a background thread after the engine was accessed from the main thread. This can lead to engine corruption and weird crashes. 

Answer 1

正如@Surjeet所说，在主线程中编写所有UI更改。

DispatchQueue.main.async {
    self.mapView.addAnnotation(self.annotation)
}