---
title: "onAvailabilityChange(perform:)"
framework: swiftui
role: symbol
role_heading: Instance Method
path: "swiftui/sceneaccessorycontent/onavailabilitychange(perform:)"
---

# onAvailabilityChange(perform:)

Defines a callback for observing the availability of self.

## Declaration

```swift
nonisolated func onAvailabilityChange(perform action: @escaping (Bool) -> Void) -> some SceneAccessoryContent

```

## Discussion

Discussion When the availability of a scene accessory changes, the specified closure will be called. For example, you can include additional controls based on the availability: struct RootView: View {     @State private var isEnabled = false     @State private var isAvailable = false     var document: PresentationDocument

var body: some View {         PresentationDocumentView(document: document)             .toolbar {                 if isAvailable {                     // Include a toolbar button to enable the                     // scene accessory when a display is available.                     SecondaryDisplayToggle(isEnabled: $isEnabled)                 }             }             .sceneAccessory {                 ExternalNonInteractiveAccessory(                     isEnabled: $isEnabled                 ) {                     PresentationPreview(document: document)                 }                 .onAvailabilityChange { newValue in                     isAvailable = newValue                 }             }     } }