19.7. Handling Conflicts in iCloud Documents
You want to be able to solve conflicts between two or more versions of a
document (managed through
otherVersionsOfItemAtURL: class method of the
NSFileVersion class to detect
different versions of the current revision of the document you are
managing using an instance of
UIDocument. Each version of a document is of
NSFileVersion. The procedure to
take is as follows:
Instantiate and open a document.
UIDocumentStateChangedNotificationnotifications (see Recipe 19.6).
Check if the
documentStateproperty of the document that caused the aforementioned notification to be fired has the
UIDocumentStateInConflictstate. If yes, then we will proceed to the next step. If not, we will handle the issue in a different way.
When a conflict occurs in a document, iCloud will automatically attempt to resolve that conflict by either merging two or more revisions of that document together, or simply taking the latest version. Whatever iCloud does, it will give you a revision of the document to work with. This revision is called the current version of that document.
We will use the
currentVersionOfItemAtURL:class method of the
NSFileVersionclass to get the current version of the document by passing the URL of the document to this method.
Next, we will use the
otherVersionsOfItemAtURL:class method of the
Versionclass to get all other versions of the document, by passing the URL of the document ...