问SwiftUI：“动态列表与组”在更改`@Published`‘属性时未刷新

EN

class Product: Identifiable, ObservableObject {
    let id = UUID()
    var name: String

    init(name: String) {
        self.name = name
    }
}

class Category: Identifiable, ObservableObject {
    let id = UUID()
    @Published var items = [Product]()
    var categoryName = ""
}

class Categories: ObservableObject {
    @Published var items = [Category]()
}

struct ProductListView: View {
    @ObservedObject var categories: Categories = Categories()


    var body: some View {
            List {
                ForEach(categories.items) { category in
                    Section(header: Text(category.categoryName)) {
                        ForEach(category.items) { item in
                            Text(item.name)
                        }
                    }
                }
            }
            .listStyle(GroupedListStyle())
    }

    func appendProduct() {
        let product = Product(name: self.$name.wrappedValue, quantity: 1, complated: false)
        let basicCategory = "Generic"
        let existingCategory = self.categories.items.filter({$0.categoryName == basicCategory}).first
        if (existingCategory?.items != nil) {

            // Changes here do not refresh the UI 
            existingCategory?.items.append(product)
        } else {
            let category = Category()
            category.categoryName = basicCategory
            category.items.append(product)
            self.categories.items.append(category)
        }
    }
}