NSKeyedArchiver

NSKeyedArchiver is a component of Apple's Foundation framework that provides a keyed archiving mechanism for encoding and decoding objects that implement the NSCoding protocol. It is used to convert an object graph into a data representation suitable for persistence, transmission, or storage, and to reconstruct the original objects from that representation.

Objects intended for archiving must implement NSCoding by providing methods to encode and initialize themselves from a coder. During encoding, properties are written with methods such as encodeObject:forKey:, encodeInteger:forKey:, encodeBool:forKey:, and other type-specific encoders. During decoding, corresponding methods like decodeObjectForKey:, decodeIntegerForKey:, and decodeBoolForKey: read the values back. The archive preserves object graphs and references using keys, enabling accurate reconstruction of the original structure.

Modern usage favors data-based archiving over file-based roots. Archiving and unarchiving are typically performed with the newer APIs, such as NSKeyedArchiver.archivedData(withRootObject:requiringSecureCoding:) to produce a Data object, and NSKeyedUnarchiver.unarchiveTopLevelObjectWithData:error: to restore objects from Data. Writing and reading from a file or network typically involves handling these Data objects. Older APIs like archiveRootObject:toFile: and unarchiveObjectWithData: are deprecated in favor of these data-oriented approaches.

Security considerations include support for NSSecureCoding. Classes should adopt NSSecureCoding and implement supportsSecureCoding to ensure that only expected object types are decoded, reducing the risk of object substitution attacks when handling data from untrusted sources.

See also: NSCoding, NSSecureCoding, NSKeyedUnarchiver.