SwiftUI：在 SplitView 中，如何检测主视图是否可见？答案

【问题标题】：SwiftUI: In SplitView, how can I detect if the master view is visible?SwiftUI：在 SplitView 中，如何检测主视图是否可见？
【发布时间】：2022-11-23 07:30:19
【问题描述】：

当 SwiftUI 创建一个 SplitView 时，它会添加一个工具栏按钮来隐藏/显示主视图。我怎样才能检测到这种变化，以便我可以调整详细信息屏幕中的字体大小并优化使用所有空间？

我试过将 .onChange 与几何一起使用，但似乎无法正常工作。

【问题讨论】：

标签： swiftui master-detail splitview

【解决方案1】：

在思考了一段时间之后，我得到了这个解决方案：

struct ContentView: View {
@State var isOpen = true

var body: some View {
    NavigationView {
        VStack{
            Text("Primary")
                .onUIKitAppear {
                    isOpen.toggle()
                }
                .onAppear{
                print("hello")
                    isOpen.toggle()
                }
                .onDisappear{
                    isOpen.toggle()
                    print("hello: bye")
                }
       .navigationTitle("options")
        }
        Text("Secondary").font(isOpen ? .body : .title)

    }.navigationViewStyle(.columns)
}


}

onUIKitAppear 是苹果建议的自定义extension，只有在视图呈现给用户https://developer.apple.com/forums/thread/655338?page=2后才执行

  struct UIKitAppear: UIViewControllerRepresentable {
     let action: () -> Void
     
     func makeUIViewController(context: Context) -> UIAppearViewController {
        let vc = UIAppearViewController()
        vc.delegate = context.coordinator
        return vc
     }
     
     func makeCoordinator() -> Coordinator {
        Coordinator(action: self.action)
     }
     
     func updateUIViewController(_ controller: UIAppearViewController, context: Context) {}
     
     class Coordinator: ActionRepresentable {
        var action: () -> Void
        init(action: @escaping () -> Void) {
              self.action = action
        }
        func remoteAction() {
              action()
        }
     }
  }

  protocol ActionRepresentable: AnyObject {
     func remoteAction()
  }

  class UIAppearViewController: UIViewController {
     weak var delegate: ActionRepresentable?
     var savedView: UIView?
     
     override func viewDidLoad() {
        self.savedView = UILabel()
        
        if let _view = self.savedView {
              view.addSubview(_view)
        }
     }
     
     override func viewDidAppear(_ animated: Bool) {
        delegate?.remoteAction()
     }
     
     override func viewDidDisappear(_ animated: Bool) {
        view.removeFromSuperview()
        savedView?.removeFromSuperview()
     }
  }

  public extension View {
     
     func onUIKitAppear(_ perform: @escaping () -> Void) -> some View {
        self.background(UIKitAppear(action: perform))
     }
  }

【讨论】：

【解决方案2】：

如果您使用的是 iOS 16，则可以使用 NavigationSplitView 和 NavigationSplitViewVisibility

例子：

struct MySplitView: View {
    @State private var columnVisibility: NavigationSplitViewVisibility = .all
    
    var bothAreShown: Bool { columnVisibility != .detailOnly }
        
    var body: some View {
        NavigationSplitView(columnVisibility: $columnVisibility) {
            Text("Master Column")
        } detail: {
            Text("Detail Column")
            Text(bothAreShown ? "Both are shown" : "Just detail shown")
        }
    }
}

【讨论】：