NSArchiver

NSArchiver is a class in the Foundation framework of Apple's Objective-C runtime environment. It is primarily used for the process of archiving, which is the serialization of object graphs into a data format. This data format can then be stored in a file or transmitted over a network. The inverse process, unarchiving, is handled by NSUnarchiver.

When an object is archived using NSArchiver, its state is converted into a byte stream. This process involves traversing the object graph, meaning that if an object contains references to other objects, those objects are also archived. This ensures that the entire structure and data of the objects are preserved. NSArchiver is particularly useful for saving application state, persisting data between application launches, or for inter-process communication.

To be archivable, objects must conform to the NSCoding protocol. This protocol requires the implementation of two methods: encode(with:) and init?(coder:). The encode(with:) method is responsible for encoding the object's properties into the encoder, while the init?(coder:) method is used by the unarchiver to reconstruct the object from the encoded data. Classes that do not conform to NSCoding cannot be directly archived.

NSArchiver is a fundamental tool for data persistence and serialization within macOS, iOS, watchOS, and tvOS applications. It provides a robust and efficient way to manage the state of complex object structures.