Swift Combine 和 SwiftUI 理解需要修正答案

【问题标题】：Swift Combine and SwiftUI understanding needs correctionsSwift Combine 和 SwiftUI 理解需要修正
【发布时间】：2020-09-03 12:44:51
【问题描述】：

我尝试做一些简单的事情。在 AppDelegate 中，我需要 var vertices: [SCNVector3] = []。在@IBAction func getVertices(_ sender: Any) 中，我可以读取文件并将新值分配给vertices。简单而有效。但是当我尝试将值传递给 SwiftUI View 时，我遇到了问题。如果我定义

@State var vertices: [SCNVector3] = []

func applicationDidFinishLaunching(_ aNotification: Notification) {
    ....
    let contentView = CloudView(data: $vertices)
    ....
    window.contentView = NSHostingView(rootView: contentView)
    ...
}

@IBAction func getVertices(_ sender: Any) {
    ...
    do {
        let readVertices: [SCNVector3] = try... // read file and convert to [SCNVector3]
        vertcices = readVertices // assign or not to assign, this is a question
        print (readVertices.count, vertices.count)
    }
    ...
}

然后打印出来：

3500 0

所以，它永远不会更新 CloudView，vertices 始终是一个空数组。

谁能解释一下我应该如何以正确的方式做到这一点？

【问题讨论】：

标签： swift swiftui combine

【解决方案1】：

您不能在 SwiftUI 视图上下文之外使用 @State。在这种情况下，最合适的是使用ObservableObject，例如

class VerticesStorage: ObservableObject {
   @Published var vertices: [SCNVector3] = []
}

然后在 AppDelegate 中

let verticesStorage = VerticesStorage()   // initialize property

func applicationDidFinishLaunching(_ aNotification: Notification) {
    ....
    let contentView = CloudView(data: verticesStorage) // inject reference
    ....
    window.contentView = NSHostingView(rootView: contentView)
    ...
}

@IBAction func getVertices(_ sender: Any) {
    ...
    do {
        let readVertices: [SCNVector3] = try... // read file and convert to [SCNVector3]

        verticesStorage.vertcices = readVertices // update here !!

        print (readVertices.count, vertices.count)
    }
    ...
}

现在在 SwiftUI 部分

struct CloudView: View {
   @ObservedObject var data: VerticesStorage     // observable !!

   var body: some View {
     // present here
   }
}

【讨论】：