The preferred filename for the file wrapper object.
- iOS 4.0+
- macOS 10.0+
- tvOS 9.0+
- watchOS 2.0+
This name is normally used as the dictionary key when a child file wrapper is added to a directory file wrapper. However, if another file wrapper with the same preferred name already exists in the directory file wrapper when this object is added, the filename assigned as the dictionary key may differ from the preferred filename.
When you change the preferred filename, the default implementation of this property causes the existing parent directory file wrappers to remove and re-add the child to accommodate the change. Preferred filenames of children are not preserved when you write a file wrapper to disk and then later instantiate another file wrapper by reading the file from disk. If you need to preserve the user-visible names of attachments, you have to store the names yourself.