# withObservationTracking(_:onChange:) Tracks access to properties. ``` func withObservationTracking(_ apply: () -> T, onChange: @autoclosure () -> @Sendable () -> Void) -> T ``` ## Parameters `apply` A closure that contains properties to track. `onChange` The closure invoked when the value of a property changes. ## Return Value The value that the `apply` closure returns if it has a return value; otherwise, there is no return value. ## Discussion This method tracks access to any property within the `apply` closure, and informs the caller of value changes made to participating properties by way of the `onChange` closure. For example, the following code tracks changes to the name of cars, but it doesn’t track changes to any other property of `Car`: ``` func render() { withObservationTracking { for car in cars { print(car.name) } } onChange: { print("Schedule renderer.") } } ``` --- 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)