cancelContentEditing()
Tells your extension to cancel editing.
Declaration
func cancelContentEditing()Discussion
Photos may call this method at any time after your extension view controller’s view appears, including while your app is preparing the editing output.
At this time, your extension should clean up any resources related to your edit and cancel any background work. If the user cancels editing while your app is preparing output, do not call the completionHandler block that Photos provided in the finishContentEditing(completionHandler:) method.