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# ABAddressBookRegisterExternalChangeCallback(_:_:_:)

Registers a callback to receive notifications when the Address Book database is modified.

```
func ABAddressBookRegisterExternalChangeCallback(_ addressBook: ABAddressBook!, _ callback: ABExternalChangeCallback!, _ context: UnsafeMutableRawPointer!)
```

## Parameters

`addressBook`

The address book used to interact with the Address Book database.

`callback`

The function to invoke when the Address Book database changes.

`context`

The object to pass to the callback function.

---

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