The environment

The environment

The environment carries values down the view tree without your handing them through every initializer on the way. A view reads a value with @Environment(\.colorScheme). An ancestor sets a value for everything beneath it with .environment(\.key, value). The system supplies many values this way: the color scheme, the size class, the locale, an action that dismisses the current screen. You add your own with the @Entry macro in an extension of EnvironmentValues. You can also place a whole @Observable object in the environment with .environment(model) and read it with @Environment(Model.self).

Use the environment for things that many views need and few of them change: a theme, a service, the current user. Do not use it to avoid deciding who owns a piece of data. A parameter in an initializer is easier to follow and easier to preview.

extension EnvironmentValues {
    @Entry var accent: Color = .orange         // a new environment value and its default
}

struct Root: View {
    var body: some View {
        Detail()
            .environment(\.accent, .purple)    // set it for everything below
    }
}

struct Detail: View {
    @Environment(\.accent) private var accent  // read it, at any depth

    var body: some View {
        Text("Hello").foregroundStyle(accent)
    }
}

Define a custom environment value for an accent color with @Entry. Set it at the root of your app, read it three levels down, and override it for one subtree only.

1. How is reading a value from the environment different from receiving it through an initializer?
2. How do you define a custom environment value?
3. What happens when a view reads an @Observable object from the environment and no ancestor provided one?

• Environment
• EnvironmentValues
• Entry() macro