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  "title" : "Notification Keys"
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# Notification Keys

Keys used to get values from the user information dictionary of the [`ALAssetsLibraryChangedNotification`](/documentation/AssetsLibrary/ALAssetsLibraryChangedNotification) notification.

## Discussion

Assets that are modified use the [`ALAssetLibraryUpdatedAssetsKey`](/documentation/AssetsLibrary/ALAssetLibraryUpdatedAssetsKey) key. Assets that are inserted or deleted use the [`ALAssetLibraryUpdatedAssetGroupsKey`](/documentation/AssetsLibrary/ALAssetLibraryUpdatedAssetGroupsKey) key for the asset group that contains the asset.

Assets and asset groups that have no strong references are omitted from the notification’s user information dictionary.

## Topics

### Constants

[`extern NSString * const ALAssetLibraryUpdatedAssetsKey;`](/documentation/AssetsLibrary/ALAssetLibraryUpdatedAssetsKey)

Value is a set of <doc://com.apple.documentation/documentation/Foundation/NSURL> objects identifying the assets that were updated.

[`extern NSString * const ALAssetLibraryInsertedAssetGroupsKey;`](/documentation/AssetsLibrary/ALAssetLibraryInsertedAssetGroupsKey)

Value is a set of <doc://com.apple.documentation/documentation/Foundation/NSURL> objects identifying the assets that were inserted.

[`extern NSString * const ALAssetLibraryUpdatedAssetGroupsKey;`](/documentation/AssetsLibrary/ALAssetLibraryUpdatedAssetGroupsKey)

Value is a set of <doc://com.apple.documentation/documentation/Foundation/NSURL> objects identifying the asset groups that were updated.

[`extern NSString * const ALAssetLibraryDeletedAssetGroupsKey;`](/documentation/AssetsLibrary/ALAssetLibraryDeletedAssetGroupsKey)

Value is a set of <doc://com.apple.documentation/documentation/Foundation/NSURL> objects identifying the asset groups that were deleted.


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