# EnvironmentKey A key for accessing values in the environment. ``` protocol EnvironmentKey ``` ## Overview You can create custom environment values by extending the [`EnvironmentValues`](/documentation/SwiftUI/EnvironmentValues) structure with new properties. First declare a new environment key type and specify a value for the required [`defaultValue`](/documentation/SwiftUI/EnvironmentKey/defaultValue) property: ``` private struct MyEnvironmentKey: EnvironmentKey { static let defaultValue: String = "Default value" } ``` The Swift compiler automatically infers the associated [`Value`](/documentation/SwiftUI/EnvironmentKey/Value) type as the type you specify for the default value. Then use the key to define a new environment value property: ``` extension EnvironmentValues { var myCustomValue: String { get { self[MyEnvironmentKey.self] } set { self[MyEnvironmentKey.self] = newValue } } } ``` Clients of your environment value never use the key directly. Instead, they use the key path of your custom environment value property. To set the environment value for a view and all its subviews, add the [`environment(_:_:)`](/documentation/SwiftUI/View/environment(_:_:)) view modifier to that view: ``` MyView() .environment(\.myCustomValue, "Another string") ``` As a convenience, you can also define a dedicated view modifier to apply this environment value: ``` extension View { func myCustomValue(_ myCustomValue: String) -> some View { environment(\.myCustomValue, myCustomValue) } } ``` This improves clarity at the call site: ``` MyView() .myCustomValue("Another string") ``` To read the value from inside `MyView` or one of its descendants, use the [`Environment`](/documentation/SwiftUI/Environment) property wrapper: ``` struct MyView: View { @Environment(\.myCustomValue) var customValue: String var body: some View { Text(customValue) // Displays "Another string". } } ``` ## Topics ### Getting the default value [`defaultValue`](/documentation/SwiftUI/EnvironmentKey/defaultValue) The default value for the environment key. [`Value`](/documentation/SwiftUI/EnvironmentKey/Value) The associated type representing the type of the environment key’s value. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)