您好我试图创建一个简单的应用程序，从我的Web服务器获取注释，然后使用它们传播地图。唯一的问题是当我在30秒后调用函数bob从另一个位置获取一个新的注释它给我上面的错误时，我尝试使用DispatchQueue.main.async修复它无济于事。任何帮助表示赞赏。
这是有问题的功能
// this is the test to see if it can add a new annotation after 30 seconds
if bob == 30{
let user_lat_temp = 26.7709
let user_lng_temp = -80.1067
DispatchQueue.main.async() {
// Do stuff to UI
self.GetAnnotations(lat: user_lat_temp, lng: user_lng_temp)
}
// reset it to see if it breaks
bob = 0
}
bob = bob + 1
print("bob: ", bob)
}
这是完整的代码
import UIKit
import MapKit
import CoreLocation
class ViewController: UIViewController, MKMapViewDelegate, CLLocationManagerDelegate {
@IBOutlet weak var mapView: MKMapView!
let access_token = ""
let manager = CLLocationManager()
var firstTime = 1
var user_lat = 0.0
var user_lng = 0.0
var bob = 0
override func viewDidLoad() {
super.viewDidLoad()
manager.delegate = self
manager.desiredAccuracy = kCLLocationAccuracyBest
manager.requestWhenInUseAuthorization()
manager.startUpdatingLocation()
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
let userLocation = locations[0]
user_lat = userLocation.coordinate.latitude
user_lng = userLocation.coordinate.longitude
self.mapView.showsUserLocation = true
if firstTime == 1{
GetAnnotations(lat: user_lat, lng: user_lng)
firstTime = 0
}
// this is the test to see if it can add a new annotation after 30 seconds
if bob == 30{
let user_lat_temp = 26.7709
let user_lng_temp = -80.1067
DispatchQueue.main.async() {
// Do stuff to UI
self.GetAnnotations(lat: user_lat_temp, lng: user_lng_temp)
}
// reset it to see if it breaks
bob = 0
}
bob = bob + 1
print("bob: ", bob)
}
func GetAnnotations(lat: Double, lng: Double){
guard let url = URL(string: "http://192.168.1.10:7888/api/?controller=location&action=get_locations") else {return}
var request = URLRequest(url: url)
request.httpMethod = "POST"
let postString = "access_token=\(access_token)&lat=\(lat)&lng=\(lng)";
request.httpBody = postString.data(using: String.Encoding.utf8)
URLSession.shared.dataTask(with: request) { (data, response, err) in
if let error = err {
print("the server is not responding \(error)")
}
if let response = response {
// if the user has a bad access token or is logged out
if let httpResponse = response as? HTTPURLResponse {
if httpResponse.statusCode == 401{
print("bad access token")
return
}
}else{
print("the server is not responding")
}
print(response)
guard let data = data else { return }
// parse the json for the locations
do {
let mapJSON = try JSONDecoder().decode(parseJsonLocations.self, from: data)
let user_id = mapJSON.user_info.user_id
print(user_id)
print(mapJSON.locations.count)
// do map
let distanceSpan:CLLocationDegrees = 10000
let userLocation:CLLocationCoordinate2D = CLLocationCoordinate2DMake(lat, lng)
self.mapView.setRegion(MKCoordinateRegionMakeWithDistance(userLocation, distanceSpan, distanceSpan), animated: true)
self.mapView.delegate = self
var i = 0
while i < mapJSON.locations.count {
let location_id = mapJSON.locations[i].location_id
let location_name = mapJSON.locations[i].location_name
let location_lat = mapJSON.locations[i].lat
let location_lng = mapJSON.locations[i].lng
let locationsLocation:CLLocationCoordinate2D = CLLocationCoordinate2DMake(location_lat, location_lng)
let subtitle = "location_id: \(location_id)"
let userAnnotation = Annotation(title: location_name, subtitle: subtitle, coordinate: locationsLocation)
self.mapView.addAnnotation( userAnnotation )
i = i + 1
}
} catch {
print("error trying to convert data to JSON")
print(error)
}
}
}.resume()
}
}
答案 0 :(得分：2)
在很多其他地方，你没有注意到你可能会遇到什么线索的问题。
你在说
if firstTime == 1 {
GetAnnotations( // ...
不确定你是否在主线上。
然后，在GetAnnotations中，你说的是
self.mapView.setRegion
// ... and all that follows ...
不确定你是否在主线上。
我并没有说你在那些时刻不在主线上，但也没有理由认为你也是。你应该检查并整理出来。
答案 1 :(得分：1)
你有正确的想法;显然在主队列上调度UI更新，遗憾的是你已经调度了错误的函数。
GetAnnotations（根据惯例应为getAnnotations）通过URLSession DataTask进行异步网络调用，并在完成处理程序中返回结果。对于像这样的网络操作，很有可能不会在主队列上调用完成处理程序，这就是这种情况。
由于完成处理程序未在主队列上执行并且您更新了UI，因此会收到错误消息。
您需要在主队列
上调度这些UI操作例如：
guard let data = data else { return }
DispatchQueue.main.async {
// parse the json for the locations
do {
let mapJSON = try JSONDecoder().decode(parseJsonLocations.self, from: data)
let user_id = mapJSON.user_info.user_id
print(user_id)
print(mapJSON.locations.count)
// do map
let distanceSpan:CLLocationDegrees = 10000
let userLocation:CLLocationCoordinate2D = CLLocationCoordinate2DMake(lat, lng)
self.mapView.setRegion(MKCoordinateRegionMakeWithDistance(userLocation, distanceSpan, distanceSpan), animated: true)
self.mapView.delegate = self
var i = 0
while i < mapJSON.locations.count {
let location_id = mapJSON.locations[i].location_id
let location_name = mapJSON.locations[i].location_name
let location_lat = mapJSON.locations[i].lat
let location_lng = mapJSON.locations[i].lng
let locationsLocation:CLLocationCoordinate2D = CLLocationCoordinate2DMake(location_lat, location_lng)
let subtitle = "location_id: \(location_id)"
let userAnnotation = Annotation(title: location_name, subtitle: subtitle, coordinate: locationsLocation)
self.mapView.addAnnotation( userAnnotation )
i = i + 1
}
} catch {
print("error trying to convert data to JSON")
print(error)
}
}
对于位置管理器委托调用，文档说明：
从您启动相应位置服务的线程调用委托对象的方法。该线程本身必须有一个活动的运行循环，就像在应用程序的主线程中找到的那样。
因此，只要您从主队列调用startUpdatingLocation，您的委托回调就会在主队列上