The file type of the document.
- iOS 5.0+
The file type is a uniform type identifier (UTI). UIKit derives the UTI from the filename-extension component of
UIKit sets this property before it calls the completion handlers of the
revert(to. If, outside of these methods or their completion handlers, you want to wait for any pending file operations to complete before you access this property, you can call
perform and access the property value in the block parameter.