我正在尝试在来自 Care Data 的 map 注释上显示多个对象。目前，我可以使用此功能获取标题和副标题来显示信息
func getData() -> [MKAnnotation]? {
do {
storedLocations = try context.fetch(Fish.fetchRequest())
var annotations = [MKAnnotation]()
for storedLocation in storedLocations {
let newAnnotation = MyAnnotation(coordinate: CLLocationCoordinate2D(latitude: storedLocation.latitude, longitude: storedLocation.longitude))
newAnnotation.coordinate.latitude = storedLocation.latitude
newAnnotation.coordinate.longitude = storedLocation.longitude
newAnnotation.title = storedLocation.species
newAnnotation.subtitle = storedLocation.length
newAnnotation.newTime = storedLocation.time
newAnnotation.newBait = storedLocation.bait
newAnnotation.newNotes = storedLocation.notes
newAnnotation.newWaterTempDepth = storedLocation.water
newAnnotation.newWeatherCond = storedLocation.weather
// print(storedLocation.length)
let newLength = storedLocation.length
let newTime = newAnnotation.newTime
// let newBait = storedLocation.bait
// let newNotes = storedLocation.notes
// let newWaterTempDepth = storedLocation.water
// let newWeatherCond = weatherCond
myLength = newLength!
myTime = newTime!
//
annotations.append(newAnnotation)
}
return annotations
}
catch {
print("Fetching Failed")
}
return nil
}
我试图在注释上显示所有存储的位置数据。
通过使用此扩展，我发现 here我可以向注释添加多行。 然而，它并非来自核心数据中存储的信息。这就是我为扩展设置 func 的方式
func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
guard !(annotation is MKUserLocation) else {
return nil
}
let reuseIdentifier = "pin"
var annotationView = map.dequeueReusableAnnotationView(withIdentifier: reuseIdentifier)
if annotationView == nil {
annotationView = MKAnnotationView(annotation: annotation, reuseIdentifier: reuseIdentifier)
annotationView?.canShowCallout = true
annotationView?.loadCustomLines(customLines: [myLength, myTime])
} else {
annotationView?.annotation = annotation
}
annotationView?.image = UIImage(named: "fish")
return annotationView
这是扩展。
extension MKAnnotationView {
func loadCustomLines(customLines: [String]) {
let stackView = self.stackView()
for line in customLines {
let label = UILabel()
label.text = line
stackView.addArrangedSubview(label)
}
self.detailCalloutAccessoryView = stackView
}
private func stackView() -> UIStackView {
let stackView = UIStackView()
stackView.axis = .vertical
stackView.distribution = .fillEqually
stackView.alignment = .fill
return stackView
}
}
这是我的注释
import UIKit
import MapKit
class MyAnnotation: NSObject, MKAnnotation {
var coordinate: CLLocationCoordinate2D
var title: String?
var subtitle: String?
var newLength: String?
var newTime: String?
var newBait: String?
var newNotes: String?
var newWaterTempDepth: String?
var newWeatherCond: String?
var detailCalloutAccessoryView: UIStackView?
init(coordinate: CLLocationCoordinate2D){
self.coordinate = coordinate
}
}
当我运行时我得到 this
我对编程非常陌生，非常感谢任何帮助，以及对我做错的事情的解释，提前谢谢您
最佳答案
'!'意味着强制展开
myLength = newLength! <- CRASH
由于这里的“newLength”为零，因此在强制解开它的地方将会发生崩溃。
例如您可以修复错误
myLength = newLength ?? 0
myTime = newTime ?? 0
另请参阅 What does "fatal error: unexpectedly found nil while unwrapping an Optional value" mean?
关于swift - 如何在 MKAnnotation 上显示核心数据中的多个项目，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/51366096/