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

Posted 2023-02-24

【中文标题】SwiftUI 将 @Published var 从一个 ObservableObject 映射到另一个

【英文标题】：SwiftUI map @Published var from one ObservableObject to another

【发布时间】：2020-08-26 16:40:33

【问题描述】：

我希望两个单独的 ObjservableObject 共享一个 @Published 变量。 理想情况下如下所示。由于Cannot assign to property: '$bar' is immutable，它无法编译。如果对其中一个或另一个进行更改，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

【参考方案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