使用Combine监听数组中对象属性变化的实现方式是否正确？

我正在开发一套监听对象变化的实现方案，当前采用以下Swift代码开发。需求是当OfferItem中的isSelected布尔属性发生变化时更新UI，想咨询这种监听数组内对象属性变化的方式是否正确。

class OfferDetail: ObservableObject {
    @Published var items: [OfferItem]
    private var anyCancellables = Set<AnyCancellable>()

    init(deliveryAddress: String, deliveryDate: String, offerItems: [OfferItem]) {
        self.items = offerItems
        for item in items {
            item.$isSelected
            .sink(receiveValue: { _ in
                print("OfferDetail Update 1")
                self.objectWillChange.send()
            })
            .store(in: &anyCancellables)
        }
    }
}

class OfferItem: Identifiable, ObservableObject {
    @Published var isSelected: Bool = false
    let uuid = UUID()
    
    init() {
        print(uuid)
    }
    
}

class ViewModel: ObservableObject {
    @Published var offer: OfferDetail?
    private var anyCancellables = Set<AnyCancellable>()

    init() {
        offer = OfferDetail(deliveryAddress: "", deliveryDate: "", offerItems: [OfferItem(), OfferItem()])
        offer?.$items.sink { items in
            print("ViewModel Update 2")
            
            for item in items {
                print(item.uuid, item.isSelected)
            }

        }.store(in: &anyCancellables)
    }
    
}

let viewModel = ViewModel()
viewModel.offer?.items.first?.isSelected = true

你的当前实现存在几个关键问题，无法完全满足需求：

1. 仅监听初始化时的数组元素：你在OfferDetail的init方法里遍历初始的items并订阅它们的isSelected变化，但如果后续数组发生增删（比如添加新的OfferItem、移除已有元素），新元素的isSelected变化不会被监听，而被移除的元素的订阅也不会被取消，会导致内存泄漏。

2. ViewModel中的$items订阅不会触发：OfferDetail里调用objectWillChange.send()只会通知OfferDetail自身的变化，但ViewModel订阅的是offer?.$items——只有当items数组本身被替换（比如重新赋值一个新数组）时，这个订阅才会触发，单个元素的属性变化不会触发$items的发布。

正确的实现方式 #

方案1：让OfferItem成为值类型（struct）

如果业务允许，将OfferItem改为struct而非class，因为值类型的属性变化会让数组元素整体变化，结合@Published可以自动触发更新：

struct OfferItem: Identifiable {
    var isSelected: Bool = false
    let id = UUID()
    
    init() {
        print(id)
    }
}

class OfferDetail: ObservableObject {
    @Published var items: [OfferItem]

    init(deliveryAddress: String, deliveryDate: String, offerItems: [OfferItem]) {
        self.items = offerItems
    }
}

class ViewModel: ObservableObject {
    @Published var offer: OfferDetail?
    private var anyCancellables = Set<AnyCancellable>()

    init() {
        offer = OfferDetail(deliveryAddress: "", deliveryDate: "", offerItems: [OfferItem(), OfferItem()])
        offer?.$items.sink { items in
            print("ViewModel Update 2")
            
            for item in items {
                print(item.id, item.isSelected)
            }
        }.store(in: &anyCancellables)
    }
}

let viewModel = ViewModel()
viewModel.offer?.items[0].isSelected = true

这种方式最简单，值类型的特性会自动帮你处理元素属性变化的通知，无需手动订阅每个元素。

方案2：保持class类型，动态监听数组元素变化

如果必须使用class类型的OfferItem，需要监听数组的变化，动态添加/移除元素的订阅：

class OfferDetail: ObservableObject {
    @Published var items: [OfferItem] {
        didSet {
            // 数组变化时，取消旧元素的订阅，订阅新元素
            cancelSubscriptions()
            subscribeToItems()
        }
    }
    private var anyCancellables = Set<AnyCancellable>()

    init(deliveryAddress: String, deliveryDate: String, offerItems: [OfferItem]) {
        self.items = offerItems
        subscribeToItems()
    }
    
    private func subscribeToItems() {
        for item in items {
            item.$isSelected
                .sink(receiveValue: { [weak self] _ in
                    print("OfferDetail Update 1")
                    self?.objectWillChange.send()
                })
                .store(in: &anyCancellables)
        }
    }
    
    private func cancelSubscriptions() {
        anyCancellables.removeAll()
    }
}

class OfferItem: Identifiable, ObservableObject {
    @Published var isSelected: Bool = false
    let id = UUID()
    
    init() {
        print(id)
    }
}

class ViewModel: ObservableObject {
    @Published var offer: OfferDetail?
    private var anyCancellables = Set<AnyCancellable>()

    init() {
        offer = OfferDetail(deliveryAddress: "", deliveryDate: "", offerItems: [OfferItem(), OfferItem()])
        // 订阅OfferDetail的objectWillChange，而非$items
        offer?.objectWillChange
            .sink { [weak self] in
                print("ViewModel Update 2")
                self?.offer?.items.forEach { item in
                    print(item.id, item.isSelected)
                }
            }
            .store(in: &anyCancellables)
    }
}

let viewModel = ViewModel()
viewModel.offer?.items.first?.isSelected = true

这里做了两个关键修改：

• 在OfferDetail的items属性添加didSet，数组变化时重新订阅所有元素
• ViewModel订阅OfferDetail的objectWillChange，这样每当OfferItem的isSelected变化时，OfferDetail发送的通知会被ViewModel接收

总结 #

如果没有特殊业务要求，优先选择方案1（值类型struct），代码更简洁且不易出错；如果必须使用引用类型，则采用方案2来动态管理元素的订阅，避免内存泄漏和监听失效。

内容的提问来源于stack exchange，提问作者Aravind Bhuvanendran