---
title: "onChange(of:perform:)"
framework: swiftui
role: symbol
role_heading: Instance Method
path: "swiftui/scene/onchange(of:perform:)"
---

# onChange(of:perform:)

Adds an action to perform when the given value changes.

## Declaration

```swift
nonisolated func onChange<V>(of value: V, perform action: @escaping (V) -> Void) -> some Scene where V : Equatable

```

## Parameters

- `value`: The value to check when determining whether to run the closure. The value must conform to the doc://com.apple.documentation/documentation/Swift/Equatable protocol.
- `action`: A closure to run when the value changes. The closure provides a single newValue parameter that indicates the changed value.

## Return Value

Return Value A scene that triggers an action in response to a change.

## Discussion

Discussion Use this modifier to trigger a side effect when a value changes, like the value associated with an Environment value or a 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.