# onChange(of:perform:) Adds an action to perform when the given value changes. ``` nonisolated func onChange(of value: V, perform action: @escaping (V) -> Void) -> some View where V : Equatable ``` ## Discussion Use this modifier to trigger a side effect when a value changes, like the value associated with an [`Environment`](/documentation/SwiftUI/Environment) value or a [`Binding`](/documentation/SwiftUI/Binding). For example, you can clear a cache when you notice that a scene moves to the background: ``` struct MyScene: Scene { @Environment(\.scenePhase) private var scenePhase @StateObject private var cache = DataCache() var body: some Scene { WindowGroup { MyRootView() } .onChange(of: scenePhase) { newScenePhase in if newScenePhase == .background { cache.empty() } } } } ``` The system may call the action closure on the main actor, so avoid long-running tasks in the closure. If you need to perform such tasks, detach an asynchronous background task: ``` .onChange(of: scenePhase) { newScenePhase in if newScenePhase == .background { Task.detached(priority: .background) { // ... } } } ``` The system passes the new value into the closure. If you need the old value, capture it in the closure. --- 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)