SwiftUI中MapKit能否从Firestore读取经纬度动态设置地图坐标

首先明确：完全可以用Firestore读取的动态坐标设置Map视图，不需要只能用静态值，你遇到的两个问题都有明确的修复方案： #

1. 修复BusinessAddressRowViewModel的shared报错 #

你代码里的public static let shared = BusinessAddressRowViewModel()完全多余，你的整个数据流是由BusinessAddressRepository监听Firestore变更，再由BusinessAddressViewModel自动生成每个地址对应的BusinessAddressRowViewModel实例，根本不需要单例，直接删除这一行即可解决参数缺失的报错。 #

2. 修复BusinessMapView不能用ViewModel坐标的问题 #

你遇到的「属性初始化不能访问其他实例属性」是Swift语法限制，有两种成熟的方案解决：

方案一：自定义视图初始化方法给@State赋初始值 #

直接在视图的init方法中，用传入的ViewModel坐标给region设置初始值，代码如下：

struct BusinessMapView: View {
    @ObservedObject var businessAddressRowViewModel: BusinessAddressRowViewModel
    @State private var region: MKCoordinateRegion
    
    // 自定义初始化方法
    init(viewModel: BusinessAddressRowViewModel) {
        self.businessAddressRowViewModel = viewModel
        // 下划线访问@State的内部存储值，完成初始化
        self._region = State(initialValue: MKCoordinateRegion(
            center: CLLocationCoordinate2D(
                latitude: viewModel.businessAddress.latitude,
                longitude: viewModel.businessAddress.longitude
            ),
            span: MKCoordinateSpan(latitudeDelta: 5.0, longitudeDelta: 5.0)
        ))
    }
            
    var body: some View {
        Map(coordinateRegion: $region)
    }
}

方案二：监听地址变更自动更新地图（更适合动态数据场景） #

如果你的业务地址可能会在Firestore中更新，建议用onReceive监听ViewModel的@Published属性变更，自动同步地图区域：

struct BusinessMapView: View {
    @ObservedObject var businessAddressRowViewModel: BusinessAddressRowViewModel
    @State private var region = MKCoordinateRegion(
        center: CLLocationCoordinate2D(latitude: 0, longitude: 0),
        span: MKCoordinateSpan(latitudeDelta: 5.0, longitudeDelta: 5.0)
    )
            
    var body: some View {
        Map(coordinateRegion: $region)
            .onReceive(businessAddressRowViewModel.$businessAddress) { newAddress in
                // 地址变更时自动更新地图区域
                region.center = CLLocationCoordinate2D(
                    latitude: newAddress.latitude,
                    longitude: newAddress.longitude
                )
            }
    }
}

调用方式 #

你在BusinessAddressView的列表中，点击某一行地址跳转地图，或者在地址行中嵌入小地图时，直接把对应位置的BusinessAddressRowViewModel实例传入即可：

// 列表中跳转示例
NavigationLink {
    BusinessMapView(viewModel: businessAddressRowViewModels[indexPath.row])
} label: {
    BusinessAddressRow(viewModel: businessAddressRowViewModels[indexPath.row])
}

内容的提问来源于stack exchange，提问作者jonthornham