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# kindKey

An `NSNumber` object that contains a value corresponding to one of the [`NSKeyValueChange`](/documentation/Foundation/NSKeyValueChange) enums, indicating what sort of change has occurred.

```
static let kindKey: NSKeyValueChangeKey
```

## Discussion

A value of [`NSKeyValueChange.setting`](/documentation/Foundation/NSKeyValueChange/setting) indicates that the observed object has received a <doc://com.apple.documentation/documentation/ObjectiveC/NSObject-swift.class/setValue(_:forKey:)> message, or that the key-value-coding-compliant set method for the key has been invoked, or that one of the <doc://com.apple.documentation/documentation/ObjectiveC/NSObject-swift.class/willChangeValue(forKey:)> or <doc://com.apple.documentation/documentation/ObjectiveC/NSObject-swift.class/didChangeValue(forKey:)> methods has otherwise been invoked.

A value of [`NSKeyValueChange.insertion`](/documentation/Foundation/NSKeyValueChange/insertion), [`NSKeyValueChange.removal`](/documentation/Foundation/NSKeyValueChange/removal), or [`NSKeyValueChange.replacement`](/documentation/Foundation/NSKeyValueChange/replacement) indicates that mutating messages have been sent a key-value observing compliant collection proxy, or that one of the key-value-coding-compliant collection mutation methods for the key has been invoked, or a collection will change or did change method has been otherwise been invoked.

You can use the [`uintValue`](/documentation/Foundation/NSNumber/uintValue) method on the `NSNumber` object to retrieve the value of the change kind.

---

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