SwiftUI 将@Published var 从一个 ObservableObject 映射到另一个

Question

我想要两个单独的ObjservableObject共享一个 @Published var。 理想情况下，如下所示。 由于Cannot assign to property: '$bar' is immutable而无法编译Cannot assign to property: '$bar' is immutable 。 如果对其中一个进行更改，我希望 foo 和 bar 保持同步。

class FooState: ObservableObject {
    @Published var foo: Bool = false
}

class BarState: ObservableObject {
    @Published var bar: Bool

    init(fooState: FooState) {
        self.$bar = fooState.$foo // compile error
    }
}

let fooState = FooState()
let barState = BarState(fooState: fooState)

print(fooState.foo) // false
print(barState.bar) // false

fooState.foo = true
print(fooState.foo) // true
print(barState.bar) // true

Answer 1

目前不支持（我认为）。 我知道解决它的唯一方法是自己订阅嵌套的可观察对象并传播objectWillChange事件：

class FooState: ObservableObject {
    @Published var foo: Bool = false
}

class BarState: ObservableObject {
    var fooState: FooState

    var bar: Bool {
        return self.fooState.foo
    }

    private var cancellables = Set<AnyCancellable>()

    init(fooState: FooState) {
        self.fooState = fooState

        fooState.objectWillChange
            .sink { [weak self] in
                self?.objectWillChange.send()
            }
            .store(in: &cancellables)
    }
}

let fooState = FooState()
let barState = BarState(fooState: fooState)

print(fooState.foo) // false
print(barState.bar) // false

fooState.foo = true
print(fooState.foo) // true
print(barState.bar) // true