How to enable secure decoding with NSKeyedUnarchiver

NSKeyedUnarchiver secure decoding.m

// It isn’t immediately obvious how to enable secure decoding with NSKeyedUnarchiver.
// NSKeyedUnarchiver has a read-write requiresSecureCoding property, but we normally use:

id decodedObject = [NSKeyedUnarchiver unarchiveObjectWithData:archive];

// so never see an instance to be able to set this property.
// However, it is quite simple. The critical part is that we use the
// normal decodeObject… methods, passing the key of the root object.

NSData *archive;
Class rootObjectClass;

NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:archive];
[unarchiver setRequiresSecureCoding:YES];
id decodedObject = [unarchiver decodeObjectOfClass:rootObjectClass forKey:NSKeyedArchiveRootObjectKey];
[unarchiver finishDecoding];

// You can verify this is right by decompiling unarchiveObjectWithData.
// If the root object is a collection, use decodeObjectOfClasses.
// finishDecoding does not do anything except notifiy the unarchiver’s delegate.