SwiftUI：@Environment 未在视图层次结构中接收提供的值

Posted 2023-02-23

【中文标题】SwiftUI：@Environment 未在视图层次结构中接收提供的值

【英文标题】：SwiftUI: @Environment not receiving provided value down the view hierarchy

【发布时间】：2021-03-23 10:59:08

【问题描述】：

我正在按照 this project 的示例创建我的 ios 应用程序（感谢 Alexey！），但无法让 @Environment 变量接收正在向下传递 UI 层次结构的值。***视图接收正确的值，但下游视图接收default 值。

编辑：在复制 Asperi 的代码之后，我发现只有在通过NavigationLink 调用下游视图时才会发生这种行为。更新以下代码：

EDIT2：问题在于调用environment 方法的位置。在NavigationView 而不是MainView 上调用它解决了这个问题。代码更新如下：

自定义环境键 - DIContainer

struct DIContainer: EnvironmentKey 
    
    let interactor: Interactor
    
    init(interactor: Interactor) 
        self.interactor = interactor
    
    
    static var defaultValue: Self  Self.default 
    
    private static let `default` = Self(interactor: .stub)


extension EnvironmentValues 
    var injected: DIContainer 
        get  self[DIContainer.self] 
        set  self[DIContainer.self] = newValue 
    

App 结构体

private let container: DIContainer

init() 
    container = DIContainer(interactor: RealInteractor())


var body: some Scene 
    WindowGroup 
        NavigationView 
            MainView()
        
        .environment(\.injected, container)

主视图

struct MainView: View 

    @Environment(\.injected) private var injected: DIContainer
    // `injected` has the `RealInteractor`, as expected

    var body: some View 
        VStack 
            Text("Main: \(injected.foo())")  \\ << Prints REAL

            NavigationLink(destination: SearchView()) 
                Text("Search")
            
        
    

搜索视图

struct SearchView: View 

    @Environment(\.injected) private var injected: DIContainer
    // `injected` has the `StubInteractor`, why?

    var body: some View 
        Text("Search: \(injected.foo())")
    

我可以通过像这样修改MainView 来解决这个问题：

    var body: some View 
        SearchView()
            .environment(\.injected, container)
    

但是@Environment的目的不是避免重复这样做吗？

任何指导/指针表示赞赏。

【参考方案1】：

我尝试复制所有部分并编译它们...结果按预期工作 - 环境在视图层次结构中向下传递，因此您可能会在实际代码中遗漏某些内容。

这是完整的模块，使用 Xcode 12.4 / iOS 14.4 测试

class Interactor                     // << replicated !!
    static let stub = Interactor()
    func foo() -> String  "stub" 


class RealInteractor: Interactor              // << replicated !!
    override func foo() -> String  "real" 


struct ContentView: View                   // << replicated !!
    private let container: DIContainer

    init() 
        container = DIContainer(interactor: RealInteractor())
    

    var body: some View 
        NavigationView 
            MainView()
        
        .environment(\.injected, container) // << to affect any links !!
    


// no changes in env parts
struct DIContainer: EnvironmentKey 

    let interactor: Interactor

    init(interactor: Interactor) 
        self.interactor = interactor
    

    static var defaultValue: Self  Self.default 

    private static let `default` = Self(interactor: .stub)


extension EnvironmentValues 
    var injected: DIContainer 
        get  self[DIContainer.self] 
        set  self[DIContainer.self] = newValue 
    


struct MainView: View 

    @Environment(\.injected) private var injected: DIContainer
    // `injected` has the `RealInteractor`, as expected

    var body: some View 
        SearchView()
    



// just tested here
struct SearchView: View 

    @Environment(\.injected) private var injected: DIContainer

    var body: some View 
        Text("Result: \(injected.interactor.foo())")     // << works fine !!
    

【讨论】：

哇！没想到任何人都会如此尽职尽责。谢谢！在我尝试复制回您的工作环境后，我发现我的 SearchView 在 NavigationLink 中被调用，这导致了问题。

在NavigationView 上调用environment 方法解决了我的问题。您能否为未来的编码人员更新您的答案，我可以接受吗？