如何从类中为 EnvironmentObject 设置值？答案

【问题标题】：How to set value to EnvironmentObject from class?如何从类中为 EnvironmentObject 设置值？
【发布时间】：2020-03-19 07:01:50
【问题描述】：

我想从 Delegate 类中为 EnvironmentObject 设置值。

struct AppleMapView: UIViewRepresentable {
  @EnvironmentObject var mapViewViewModel: MapViewViewModel
  let mapViewDelegate = MapViewDelegate()
  class MapViewDelegate: NSObject, MKMapViewDelegate {
    func mapView(_ mapView: MKMapView, didChange mode: MKUserTrackingMode, animated: Bool) {
     // This is where I want to set value to EnvObj
     **mapViewViewModel.mode = mode**
    }
  }
}

这就是我想做的。

我的代码报错

Instance member 'mapViewViewModel' of type 'AppleMapView' cannot be used on instance of nested type 'AppleMapView.MapViewDelegate'

所以，我尝试引用委托类：

MapViewDelegate(vm: mapViewViewModel) 这没有编译错误，但是当我运行代码时它出错了

A View.environmentObject(_:) for MapViewViewModel may be missing as an ancestor of this view.: file /BuildRoot/Library/Caches/com.apple.xbs/Sources/Monoceros_Sim/Monoceros-39.4.3/Core/EnvironmentObject.swift, line 55 ```

两者都不起作用。如何修复我的代码？

【问题讨论】：

标签： ios swift swiftui

【解决方案1】：

它的工作方式不同，它需要让您的MapViewDelegate 成为AppleMapView 的协调员，如下所示

struct AppleMapView: UIViewRepresentable {
  @EnvironmentObject var mapViewViewModel: MapViewViewModel

    func makeUIView(context: Context) -> MKMapView {
        let mapView = MKMapView()
        mapView.delegate = context.coordinator // << your delegate
        return mapView
    }

    func makeCoordinator() -> MapViewDelegate {
        MapViewDelegate(self)   // << will be created for you
    }

  class MapViewDelegate: NSObject, MKMapViewDelegate {
    var owner: AppleMapView
    init(_ owner: AppleMapView) {
      self.owner = owner
    }
    func mapView(_ mapView: MKMapView, didChange mode: MKUserTrackingMode, animated: Bool) {
       owner.mapViewViewModel.mode = mode // << now you have access to owner props
    }
  }
}

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