---
title: "observeValue(forKeyPath:of:change:context:)"
framework: objectivec
role: symbol
role_heading: Instance Method
path: "objectivec/nsobject-swift.class/observevalue(forkeypath:of:change:context:)"
---

# observeValue(forKeyPath:of:change:context:)

Informs the observing object when the value at the specified key path relative to the observed object has changed.

## Declaration

```swift
func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?)
```

## Parameters

- `keyPath`: The key path, relative to object, to the value that has changed.
- `object`: The source object of the key path keyPath.
- `change`: A dictionary that describes the changes that have been made to the value of the property at the key path keyPath relative to object. Entries are described in Change Dictionary Keys.
- `context`: The value that was provided when the observer was registered to receive key-value observation notifications.

## Discussion

Discussion For an object to begin sending change notification messages for the value at keyPath, you send it an addObserver(_:forKeyPath:options:context:) message, naming the observing object that should receive the messages. When you are done observing, and in particular before the observing object is deallocated, you send the observed object a removeObserver(_:forKeyPath:) or removeObserver(_:forKeyPath:context:) message to unregister the observer, and stop sending change notification messages.