SwiftUI ObservableObject 用作 EnvironmentObject 奇怪的行为

Question

我有这样的 ObservableObject，我正在使用 environmentObject().

注入视图层次结构

class MenuModel: ObservableObject {

    @Published var selection: Int = 0
    @Published var isMenuOpen: Bool = false

    @Published var tabItems : [TabItem] = [TabItem]()
//    {
//        didSet {
//            objectWillChange.send()
//        }
//    }
    @Published var menuItems : [MenuItem] = [MenuItem]()
//    {
//        didSet {
//            objectWillChange.send()
//        }
//    }

    //var objectWillChange = PassthroughSubject<Void, Never>()
}

以下是我不太了解的问题： 1. 上面的代码可以正常工作，因为所有属性都是@Published。 2. 但是如果我把它改成这样

class Click5MenuModel: ObservableObject {

    @Published var selection: Int = 0
    @Published var isMenuOpen: Bool = false

    var tabItems : [TabItem] = [TabItem]()
    {
        didSet {
            objectWillChange.send()
        }
    }
    var menuItems : [MenuItem] = [MenuItem]()
    {
        didSet {
            objectWillChange.send()
        }
    }

    var objectWillChange = PassthroughSubject<Void, Never>()
}

然后@Published 属性停止刷新依赖于此 ObservableObject 的视图！这是为什么。我还尝试添加 didSet 和 objectWillChange.send() 但这也会导致一些奇怪的行为并且代码有点尴尬。

这是否意味着我只能使用 ONLY @Published 或 ONLY objectWillChange 方法？

Answer 1

默认实现就可以工作（只要你有@Published 属性）。这是来自 API 声明：

/// By default an `ObservableObject` will synthesize an `objectWillChange`
/// publisher that emits before any of its `@Published` properties changes:
...
@available(iOS 13.0, OSX 10.15, tvOS 13.0, watchOS 6.0, *)
extension ObservableObject where Self.ObjectWillChangePublisher == ObservableObjectPublisher {

    /// A publisher that emits before the object has changed.
    public var objectWillChange: ObservableObjectPublisher { get }
}

所以删除以下内容：

var objectWillChange = PassthroughSubject<Void, Never>()

并使用

didSet {
    self.objectWillChange.send()
}

SwiftUI ObservableObject 用作 EnvironmentObject 奇怪的行为

SwiftUI ObservableObject used as EnvironmentObject odd behaviour

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SwiftUI ObservableObject 用作​​ EnvironmentObject 奇怪的行为

SwiftUI ObservableObject used as EnvironmentObject odd behaviour

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SwiftUI ObservableObject 用作 EnvironmentObject 奇怪的行为