NavigationSplitView中传递的selectedBook状态变量为何不更新？

切换NavigationSplitView的选中人物时，SwiftUI可能会复用PersonView的视图实例，导致其内部@State var selectedBook保留了上一次的选中值，没有自动重置为新人物的默认书籍；同时BooksDisclosure的onAppear方法因视图复用未触发，无法更新选中状态。

1. 强制重建PersonView重置状态 #

给PersonView添加id绑定到当前选中人物，确保切换人物时SwiftUI销毁旧视图、创建新视图，彻底重置selectedBook状态：

struct PersonView: View {
    private(set) var selectedPerson: Person
    
    @State private var selectedBook: Book?
    
    var body: some View {
        List {
            BooksDisclosure(person: selectedPerson, selectedBook: $selectedBook)
        }
        .listStyle(.insetGrouped)
        .id(selectedPerson) // 绑定视图标识到选中人物，切换时强制重建
    }
}

2. 优化书籍查询逻辑（可选但推荐） #

原代码中BooksDisclosure先全局查询所有书籍再过滤，效率较低且依赖外部数组传递。改为直接关联当前人物，用@Query精准查询：

struct BooksDisclosure: View {
    private let person: Person
    @Binding var selectedBook: Book?
    
    @Query(sort: \Book.name) private var queriedBooks: [Book]
    @State var disclosureIsExpanded: Bool = false
    
    private var filteredAndSortedBooks: [Book] {
        queriedBooks.filter { $0.customer == person }
    }
    
    var body: some View {
        DisclosureGroup(isExpanded: $disclosureIsExpanded) {
            ForEach(filteredAndSortedBooks) { book in
                HStack {
                    Button(action: {
                        selectedBook = book
                        disclosureIsExpanded = false
                    }) {
                        Text(book.name)
                    }
                    .buttonStyle(PlainButtonStyle())
                    
                    if selectedBook == book {
                        Image(systemName: "checkmark")
                    }
                    
                    Spacer()
                }
            }
        } label: {
            Text("Currently Reading: ")
            if let selectedBook = selectedBook {
                Text(selectedBook.name)
            } else {
                Text("None")
            }
        }
        .onAppear {
            selectedBook = filteredAndSortedBooks.first
        }
    }
    
    init(person: Person, selectedBook: Binding<Book?>) {
        self.person = person
        self._selectedBook = selectedBook
        // 初始化时设置查询过滤条件，只查当前人物的书籍
        self._queriedBooks = Query(filter: #Predicate<Book> { $0.customer == person })
    }
}

3. 简化冗余逻辑 #

移除原按钮中多余的条件判断，直接赋值即可：

// 原冗余代码
if selectedBook != book {
    selectedBook = book
}
if disclosureIsExpanded != true {
    disclosureIsExpanded = false
}

// 简化后
selectedBook = book
disclosureIsExpanded = false

添加id(selectedPerson)是解决状态不更新的关键：它让SwiftUI将每个人物对应的PersonView视为独立视图，切换时必须重建，从而重置selectedBook的初始状态；后续BooksDisclosure的onAppear会触发，将选中书籍设置为新人物的第一本书。

内容的提问来源于stack exchange，提问作者Ser Pounce