对 SwiftUI 中的 @EnvironmentObject 感到困惑

Question

我正在尝试在 SwiftUI 中练习 @EnvironmentObject 工具。
ContentView 中的共享对象 User init。
当我从 ContentView 切换到 NameView 时工作得很好。
但是，从 NameView 到 AgeView 失败了。 （请查看错误消息和代码会话）

错误信息

Fatal error: No ObservableObject of type User found.

有人可以给我建议吗？我错过了什么吗？谢谢

代码

init "User" type in contentView
NavigationView

+-----------+                   +--------+                   +-------+
|ContentView+--NavigationLink-->|NameView+--NavigationLink-->|AgeView|
+-----------+                   +--------+                   +-------+

final class User: ObservableObject {
    @Published var name: String
    @Published var age: Int

    init(name: String, age: Int) {
        self.name = name
        self.age = age
    }
}

struct ContentView: View {
    var user: User = User(name: "SomeName", age: 44)
    var body: some View {
        NavigationView {
            VStack {
                Text("name: \(self.user.name) age: \(self.user.age)")
                NavigationLink(destination: NameView().environmentObject(self.user)) {
                    Text("Show Name")
                }
            }
        }
    }
}

struct NameView: View {
    @EnvironmentObject var user: User
    var body: some View {
        VStack {
            Text("name: \(self.user.name)")
            NavigationLink(destination: AgeView()) {
                Text("Show Age")
            }
        }
    }
}

struct AgeView: View {
    @EnvironmentObject var user: User
    var body: some View {
        VStack {
            Text("age: \(self.user.age)")
        }
    }
}

Answer 1

希望这可以帮助您了解以下示例：

我们的模型是Observable，并且所有变量已发布：

class A: ObservableObject {
    @Published var id: String = ""
    @Published var value: String = ""
}

当将其用作 EnvironmentObject 时，请确保在 SceneDelegate.swift 中进行如下设置：

let example = Example()

    if let windowScene = scene as? UIWindowScene {
        let window = UIWindow(windowScene: windowScene)
        window.rootViewController = UIHostingController(rootView: example.environmentObject(A()))
        self.window = window
        window.makeKeyAndVisible()
    }

然后我们可以在所有视图中使用这个EnvironmentObject：

struct Example: View {

    @EnvironmentObject var obj: A

    var body: some View {
        Button(action: {
            self.obj.value = "Hi im changed"
        }) {
            Text("Change me")
        }
    }
}

有时当你想更新这个对象中的数据时，xCode 可能会给你一个错误'No EnvironmentObject set for ... classname etc.'，在这种情况下你需要传递一个 EnvironmentObject到目标视图：

DestinationView().environmentObject(self.A)

希望这会有所帮助，祝你好运！

Answer 2

您正在将 SceneDelegate 中的 EnvironmentObject 分配给 ContentView，因此 ContentView 的所有子视图都可以自动访问您的用户。

因此没有必要像这里一样再次传递它：NameView().environmentObject(self.user)

如果您在 .sheet 修饰符中显示 View ，您只需要再次传递 environmentObject ，因为它基本上是一个新的独立视图。

final class User: ObservableObject {
    @Published var name: String
    @Published var age: Int

    init(name: String, age: Int) {
        self.name = name
        self.age = age
    }
}

struct ContentView: View {
    @EnvironmentObject var user: User
    var body: some View {
        NavigationView {
            VStack {
                Text("name: \(self.user.name) age: \(self.user.age)")
                NavigationLink(destination: NameView()) {
                    Text("Show Name")
                }
            }
        }
    }
}

struct NameView: View {
    @EnvironmentObject var user: User
    var body: some View {
        VStack {
            Text("name: \(self.user.name)")
            NavigationLink(destination: AgeView()) {
                Text("Show Age")
            }
        }
    }
}

struct AgeView: View {
    @EnvironmentObject var user: User
    var body: some View {
        VStack {
            Text("age: \(self.user.age)")
        }
    }
}