SwiftUI中@EnvironmentObject的混淆

Question

我正在尝试在@EnvironmentObject中使用SwiftUI工具。

共享对象User init在ContentView中。

当我从ContentView切换到NameView时，效果很好。

但是，从NameView到AgeView都失败了。(请查看错误消息和代码会话)

错误消息

Fatal error: No ObservableObject of type User found.

有人能给我建议吗？我错过了什么吗？thx

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

希望这可以帮助您完成以下示例：

我们有我们的模型，它是可观测的，它的所有变量都是发布的

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

当将它作为EnvironmentObject使用时，请确保在SceneDelegate.swift中设置如下所示：

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，当您想要更新此对象中的数据时，xCode可能会给出一个关于'No EnvironmentObject set for . classname等‘的错误，在这种情况下，您需要将一个EnvironmentObject传递给目标视图：

DestinationView().environmentObject(self.A)

希望这能帮上忙古德勒克！

Answer 2

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

因此，再次传递它是不必要的，如这里所示：NameView().environmentObject(self.user)

如果在environmentObject修饰符中显示视图，则只需要再次传递.sheet，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)")
        }
    }
}