添加MapUserTrackingMode引发SwiftUI视图初始化错误问题

这两个错误和添加MapUserTrackingMode没有直接关联，本质是**@State属性的初始化方式不符合Swift结构体初始化规则**：

• Swift要求结构体的所有存储属性必须在self可用之前完成初始化，你当前在init里先赋值self.location，再用self.location初始化mapRegion，此时self还未完全初始化，编译器判定self.location被提前使用。
• 直接给@State属性赋值self.location = location不是正确的初始化方式，@State属性需要通过其底层的State结构体来初始化。

解决方案1：正确初始化@State底层存储 #

修改init方法，直接初始化@State对应的下划线前缀属性，同时避免依赖未完全初始化的self：

struct LocationInfoView: View {

  @State var location: CLLocationCoordinate2D
  @State private var mapRegion: MKCoordinateRegion
  @State private var trackingMode = MapUserTrackingMode.follow
  let markers: [Marker]

  init(location: CLLocationCoordinate2D) {
    // 初始化@State的底层存储
    _location = State(initialValue: location)
    // 用传入的参数直接创建区域，不依赖self.location
    let initialRegion = MKCoordinateRegion(center: location, span: MKCoordinateSpan(latitudeDelta: 0.00625, longitudeDelta: 0.00625))
    _mapRegion = State(initialValue: initialRegion)
    markers = [Marker(location: MapPin(coordinate: location))]
  }

  var body: some View {
    Map(
      coordinateRegion: $mapRegion,
      showsUserLocation: true,
      userTrackingMode: $trackingMode,
      annotationItems: markers) { marker in
        marker.location
      }
      .edgesIgnoringSafeArea(.bottom)
  }
}

struct Marker: Identifiable {
  let id = UUID()
  var location: MapPin
}

解决方案2：简化状态设计（如果location不需要修改） #

如果location只是初始化参数，不需要作为可修改的状态，直接去掉@State修饰，初始化逻辑会更简洁：

struct LocationInfoView: View {

  let location: CLLocationCoordinate2D // 移除@State
  @State private var mapRegion: MKCoordinateRegion
  @State private var trackingMode = MapUserTrackingMode.follow
  let markers: [Marker]

  init(location: CLLocationCoordinate2D) {
    self.location = location
    mapRegion = MKCoordinateRegion(center: location, span: MKCoordinateSpan(latitudeDelta: 0.00625, longitudeDelta: 0.00625))
    markers = [Marker(location: MapPin(coordinate: location))]
  }

  var body: some View {
    Map(
      coordinateRegion: $mapRegion,
      showsUserLocation: true,
      userTrackingMode: $trackingMode,
      annotationItems: markers) { marker in
        marker.location
      }
      .edgesIgnoringSafeArea(.bottom)
  }
}

struct Marker: Identifiable {
  let id = UUID()
  var location: MapPin
}

内容的提问来源于stack exchange，提问作者HarryMoy