Environment

struct · iOS 13.0+ · SDK 27.1

@frozen @propertyWrapper struct Environment<Value>

A property wrapper that reads a value from a view's environment. Use the `Environment` property wrapper to read a value stored in a view's environment. Indicate the value to read using an ``EnvironmentValues`` key path in the property declaration. For example, you can create a property that reads the color scheme of the current view using the key path of the ``EnvironmentValues/colorScheme`` property: @Environment(\.colorScheme) var colorScheme: ColorScheme You can condition a view's content on the associated value, which you read from the declared property's ``wrappedValue``. As with any property wrapper, you access the wrapped value by directly referring to the property: if colorScheme == .dark { // Checks the wrapped value. DarkContent() } else { LightContent() } If the value changes, SwiftUI updates any parts of your view that depend on the value. For example, that might happen in the above example if the user changes the Appearance settings. You can use this property wrapper to read --- but not set --- an environment value. SwiftUI updates some environment values automatically based on system settings and provides reasonable defaults for others. You can override some of these, as well as set custom environment values that you define, using the ``View/environment(_:_:)`` view modifier. For the complete list of environment values SwiftUI provides, see the properties of the ``EnvironmentValues`` structure. For information about creating custom environment values, see the ``Entry()`` macro. ### Get an observable object You can also use `Environment` to get an observable object from a view's environment. The observable object must conform to the <doc://com.apple.documentation/documentation/Observation/Observable> protocol, and your app must set the object in the environment using the object itself or a key path. To set the object in the environment using the object itself, use the ``View/environment(_:)`` modifier: @Observable class Library { var books: [Book] = [Book(), Book(), Book()] var availableBooksCount: Int { books.filter(\.isAvailable).count } } @main struct BookReaderApp: App { @State private var library = Library() var body: some Scene { WindowGroup { LibraryView() .environment(library) } } } To get the observable object using its type, create a property and provide the `Environment` property wrapper the object's type: struct LibraryView: View { @Environment(Library.self) private var library var body: some View { // ... } } By default, reading an object from the environment returns a non-optional object when using the object type as the key. This default behavior assumes that a view in the current hierarchy previously stored a non-optional instance of the type using the ``View/environment(_:)`` modifier. If a view attempts to retrieve an object using its type and that object isn't in the environment, SwiftUI throws an exception. In cases where there is no guarantee that an object is in the environment, retrieve an optional version of the object as shown in the following code. If the object isn't available the environment, SwiftUI returns `nil` instead of throwing an exception. @Environment(Library.self) private var library: Library? ### Get an observable object using a key path To set the object with a key path, use the ``View/environment(_:_:)`` modifier: @Observable class Library { var books: [Book] = [Book(), Book(), Book()] var availableBooksCount: Int { books.filter(\.isAvailable).count } } @main struct BookReaderApp: App { @State private var library = Library() var body: some Scene { WindowGroup { LibraryView() .environment(\.library, library) } } } To get the object, create a property and specify the key path: struct LibraryView: View { @Environment(\.library) private var library var body: some View { // ... } }

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