---
title: "withObservationTracking(_:onChange:)"
framework: observation
role: symbol
role_heading: Function
path: "observation/withobservationtracking(_:onchange:)"
---

# withObservationTracking(_:onChange:)

Tracks access to properties.

## Declaration

```swift
func withObservationTracking<T>(_ 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

Return Value The value that the apply closure returns if it has a return value; otherwise, there is no return value.

## Discussion

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.")     } }

## See Also

### Change tracking

- [ObservationRegistrar](observation/observationregistrar.md)