使 SwiftUI 文档可用作 EnvironmentObject

Question

我正在使用FileDocument读取文件文档。 该文档可通过绑定到最顶层视图获得：

struct ContentView: View {
    @Binding var document: SomeDocument
    var body: some View {
        Text(self.document.someString)
        NestedChildViews().environmentObject(self.document)
    } 
}

有没有办法将文档的@Binding转换为@EnvironmentObject以使其可用于所有嵌套视图？ 简单地用@Binding @EnvironmentObject行不通的，因为FileDocument是一个结构。

Property type 'SomeDocument' does not match that of the 'wrappedValue' property of its wrapper type 'EnvironmentObject'

在ContentView中创建作为@StateObject创建的中间ObservableObject将不起作用，因为它必须在 Binding to document 可用之前启动：

struct ContentView: View {
    @Binding var document: SomeDocument
    @StateObject var sharedState = SomeSharedState(document: self.document) // won't work
}

在文档和一系列嵌套视图之间不传递所有级别之间的绑定的最佳方法是什么？

Answer 1

您应该在视图的 init 中初始化@StateObject ，因为您将document传递到 init 中：

struct ContentView: View {
    
    @Binding var document: SomeDocument
    @StateObject var sharedState: SomeSharedState
    
    init(document: Binding<SomeDocument>) {
        _document = document
        _sharedState = StateObject(wrappedValue: SomeSharedState(document: document.projectedValue))
    }
    
    var body: some View {
        Text(document.someString)
            .environmentObject(sharedState)
            
            /* TEST TO SHOW IT WORKS
            .onAppear {
                DispatchQueue.main.asyncAfter(deadline: .now() + 3) {
                    document = SomeDocument(someString: "New!")
                }
            }
            */
    }
}

class SomeSharedState: ObservableObject {
    @Published var document: Binding<SomeDocument>
    
    init(document: Binding<SomeDocument>) {
        _document = Published(initialValue: document)
    }
}