SwiftUI地图视图初始化报错：self变量未初始化问题求助

我正在开发一款在地图上显示溜冰场的App，参考了Hacking with Swift的Map View标注教程，当前尝试添加自定义标注（暂使用City类）时，在init函数中出现两个错误：

• Variable 'self.iceRink' used before being initialized
• Variable 'self.region' used before being initialized

完整错误代码 #

import SwiftUI
import CoreLocation
import MapKit

struct IceRink: Identifiable {
    let id = UUID()
    let name: String
    let lat: Double
    let lng: Double
}

struct City: Identifiable {
    let id = UUID()
    let name: String
    let coordinate: CLLocationCoordinate2D
}

struct IceRinkView: View {
    @State private var iceRink: IceRink
    @State private var region: MKCoordinateRegion
    private let annotations: [City]
    
    init(iceRink: IceRink) {
        self.iceRink = iceRink
        region = MKCoordinateRegion(center: CLLocationCoordinate2D(latitude: iceRink.lat, longitude: iceRink.lng), span: MKCoordinateSpan(latitudeDelta: 10, longitudeDelta: 10))
        
        annotations = [
                City(name: "London", coordinate: CLLocationCoordinate2D(latitude: 51.507222, longitude: -0.1275)),
                City(name: "Paris", coordinate: CLLocationCoordinate2D(latitude: 48.8567, longitude: 2.3508)),
                City(name: "Rome", coordinate: CLLocationCoordinate2D(latitude: 41.9, longitude: 12.5)),
                City(name: "Washington DC", coordinate: CLLocationCoordinate2D(latitude: 38.895111, longitude: -77.036667)),
                City(name:  iceRink.name, coordinate: CLLocationCoordinate2D(latitude: iceRink.lat, longitude: iceRink.lng))
            ]
    }
    
    var body: some View {
        VStack {
            Text(iceRink.name)
            
            Map(coordinateRegion: $region, annotationItems: annotations) {
                MapPin(coordinate: $0.coordinate)
            }
            .frame(width: 300, height: 300)
        }
    }
}

struct IceRinkView_Previews: PreviewProvider {
    static var previews: some View {
        let iceRink = IceRink(name: "Cardiff", lat: 51.48439917004662, lng: -3.177987950883214)
        IceRinkView(iceRink: iceRink)
    }
}

错误截图 #

问题原因与修复方案 #

错误根源在于**@State属性的初始化方式错误以及存储属性初始化顺序不符合Swift要求**：

1. iceRink是从外部传入的固定数据，不需要用@State修饰（@State仅用于视图内部可修改的状态），应改为普通let属性。
2. 对于@State修饰的region，必须通过_region = State(initialValue: ...)的方式在init中初始化，直接赋值会触发初始化顺序错误。

修改后的正确代码 #

import SwiftUI
import CoreLocation
import MapKit

struct IceRink: Identifiable {
    let id = UUID()
    let name: String
    let lat: Double
    let lng: Double
}

struct City: Identifiable {
    let id = UUID()
    let name: String
    let coordinate: CLLocationCoordinate2D
}

struct IceRinkView: View {
    private let iceRink: IceRink // 移除@State，改为固定常量
    @State private var region: MKCoordinateRegion
    private let annotations: [City]
    
    init(iceRink: IceRink) {
        self.iceRink = iceRink
        // 正确初始化@State属性
        self._region = State(initialValue: MKCoordinateRegion(
            center: CLLocationCoordinate2D(latitude: iceRink.lat, longitude: iceRink.lng),
            span: MKCoordinateSpan(latitudeDelta: 10, longitudeDelta: 10)
        ))
        
        annotations = [
                City(name: "London", coordinate: CLLocationCoordinate2D(latitude: 51.507222, longitude: -0.1275)),
                City(name: "Paris", coordinate: CLLocationCoordinate2D(latitude: 48.8567, longitude: 2.3508)),
                City(name: "Rome", coordinate: CLLocationCoordinate2D(latitude: 41.9, longitude: 12.5)),
                City(name: "Washington DC", coordinate: CLLocationCoordinate2D(latitude: 38.895111, longitude: -77.036667)),
                City(name: iceRink.name, coordinate: CLLocationCoordinate2D(latitude: iceRink.lat, longitude: iceRink.lng))
            ]
    }
    
    var body: some View {
        VStack {
            Text(iceRink.name)
            
            Map(coordinateRegion: $region, annotationItems: annotations) {
                MapPin(coordinate: $0.coordinate)
            }
            .frame(width: 300, height: 300)
        }
    }
}

struct IceRinkView_Previews: PreviewProvider {
    static var previews: some View {
        let iceRink = IceRink(name: "Cardiff", lat: 51.48439917004662, lng: -3.177987950883214)
        IceRinkView(iceRink: iceRink)
    }
}

内容的提问来源于stack exchange，提问作者marmite