Create enumerators to specify your file provider's content, and track changes to that content.
To display your file provider's items to the user, you tell the system about those items and any changes to their contents. You do this by providing enumerators.
To provide an enumerator, create a class that adopts the
NSFile protocol. The system uses this enumerator to represent an item (a folder or a document) managed by your file provider. In addition, the system uses the enumerator to track any changes to the item.
The system also uses an enumerator to track the working set (a set of special items like Recents or Favorites).
You create enumerators to handle these use cases:
You are passed...
Your enumerator returns...
The user begins browsing your file provider's content
The content of your file provider's root directory, and any changes to that content
The user opens a new folder while browsing your file provider's content
The folder's persistent identifier
The content of the specified folder, and any changes to its content
The user opens a document from your file provider
The document's persistent identifier
Changes to the open document
The system is alerted to changes to the working set
The content of your working set, and any changes to that content
Once requested, an enumerator is used to provide both the content and any changes for an item. When the system is finished with the item, it calls the enumerator’s
invalidate() method. For example, if you return an enumerator that provides the content of a directory, as long as the enumerator is active, the system also uses it to enumerate changes to the directory.
The system may have multiple, active enumerators for a number of different items. Some of these may represent items that are currently displayed on screen. Others may be items that are no longer displayed, but the enumerator is retained for performance reasons. You need to inform the system of any changes to the content managed by any of the active enumerators, as well as any changes to the working set (whether or not it has an active enumerator).