SwiftUI中LocationManager类override init初始化报错求助

问题描述 #

实现基于CoreLocation的LocationManager类时，引入PlaceLibrary实例后，override init()报错：

Property 'self.placeLibrary' not initialized at super.init call

尝试在super.init()前后添加self.placeLibrary = placeLibrary均无效。

错误原因 #

1. Swift初始化规则限制：子类的所有存储属性必须在调用super.init()之前完成初始化。原代码中placeLibrary是未初始化的非可选存储属性，且在super.init()前还尝试访问placeLibrary.testPlace，违反了初始化规则。
2. @ObservedObject使用错误：@ObservedObject是用于View中观察ObservableObject的属性包装器，在LocationManager这类非View类中不需要使用，直接持有实例即可。
3. 无效的赋值语句：原代码中self.placeLibrary = placeLibrary的右侧placeLibrary未定义，属于无效赋值。

解决方案 #

方案1：通过初始化参数传入PlaceLibrary实例 #

修改LocationManager的初始化方法，接收PlaceLibrary作为参数，在super.init()前完成属性初始化，同时移除@ObservedObject包装器：

import Foundation
import CoreLocation
import Combine
import SwiftUI

class LocationManager: NSObject, ObservableObject, CLLocationManagerDelegate {

    private let locationManager = CLLocationManager()
    
    // 直接持有PlaceLibrary实例，移除@ObservedObject
    let placeLibrary: PlaceLibrary
    
    @Published var locationStatus: CLAuthorizationStatus?
    @Published var lastLocation: CLLocation?
    @Published var distanceFromNearest: Double = 0.0
    @Published var nearestObject: String = ""
    
    // 修改初始化方法，接收PlaceLibrary参数
    init(placeLibrary: PlaceLibrary) {
        // 先初始化自身存储属性，再调用super.init()
        self.placeLibrary = placeLibrary
        super.init()
        locationManager.delegate = self
        locationManager.desiredAccuracy = kCLLocationAccuracyBest
        locationManager.requestWhenInUseAuthorization()
        locationManager.startUpdatingLocation()
    }
    
    var statusString: String {
        guard let status = locationStatus else {
            return "unknown"
        }
        
        switch status {
        case .notDetermined: return "notDetermined"
        case .authorizedWhenInUse: return "authorizedWhenInUse"
        case .authorizedAlways: return "authorizedAlways"
        case .restricted: return "restricted"
        case .denied: return "denied"
        default: return "unknown"
        }
    }

    func locationManager(_ manager: CLLocationManager, didChangeAuthorization status: CLAuthorizationStatus) {
        locationStatus = status
        print(#function, statusString)
    }
    
    func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
        guard let location = locations.last else { return }
        lastLocation = location
        
        for (idx, _) in placeLibrary.testPlace.enumerated() {
            let currentLocation = CLLocation(latitude: location.coordinate.latitude, longitude: location.coordinate.longitude)
            let comparedLocation = CLLocation(latitude: placeLibrary.testPlace[idx].lat, longitude: placeLibrary.testPlace[idx].long)

            placeLibrary.testPlace[idx].proximity = currentLocation.distance(from: comparedLocation)
        }
        
        placeLibrary.testPlace = placeLibrary.testPlace.sorted(by: { $0.proximity < $1.proximity })
        
        print(placeLibrary.testPlace)
    }
}

在View中使用时，需先创建PlaceLibrary实例，再传入LocationManager：

struct ContentView: View {
    @StateObject private var placeLibrary = PlaceLibrary()
    @StateObject private var locationManager: LocationManager
    
    init() {
        _locationManager = StateObject(wrappedValue: LocationManager(placeLibrary: placeLibrary))
    }
    
    var body: some View {
        Text("Location Status: \(locationManager.statusString)")
    }
}

方案2：将PlaceLibrary设为单例 #

如果PlaceLibrary在全局只需要一个实例，可以将其改为单例，这样LocationManager可以直接在初始化时获取单例：

修改PlaceLibrary：

class PlaceLibrary: ObservableObject{
    // 单例实例
    static let shared = PlaceLibrary()
    
    @Published var testPlace = [
        Place(lat: 46.1810, long: 6.2304, Name: "Place 1", proximity: 0.0),
        Place(lat: 46.1531, long: 6.2951, Name: "Place 2", proximity: 0.0),
        Place(lat: 46.1207, long: 6.3302, Name: "Place 3", proximity: 0.0)
    ]
    
    // 私有初始化方法，避免外部创建实例
    private init() {}
}

修改LocationManager的初始化：

override init() {
    self.placeLibrary = PlaceLibrary.shared
    super.init()
    locationManager.delegate = self
    locationManager.desiredAccuracy = kCLLocationAccuracyBest
    locationManager.requestWhenInUseAuthorization()
    locationManager.startUpdatingLocation()
}

这样在View中可以直接初始化LocationManager：

struct ContentView: View {
    @StateObject private var locationManager = LocationManager()
    
    var body: some View {
        Text("Location Status: \(locationManager.statusString)")
    }
}

内容的提问来源于stack exchange，提问作者flyer74