encodeWithCoder

encodeWithCoder is a method in the NSCoding protocol of Apple's Foundation framework. It is called when an object is being archived or serialized by an archiver such as NSKeyedArchiver. The method's purpose is to encode the receiver's property values into the provided coder so the object can be reconstructed later.

To decode the object, the corresponding initializer initWithCoder: in Objective-C or the initializer init(coder:) in Swift is implemented. Together they enable persistence and interprocess communication by transforming objects into a storable format and back.

In implementing encodeWithCoder, each property should be encoded with a key using the appropriate coder method, for example encoding an object or primitive values. If the class has a superclass that implements NSCoding, the implementation should typically invoke the superclass's encodeWithCoder: as part of its own encoding process, to ensure the entire object graph is encoded.

Keyed archivers (NSKeyedArchiver) are the common form of archiving and rely on string keys to pair with the decoded values. Non-keyed archivers existed but are less commonly used after the introduction of keyed archiving. For secure coding, NSSecureCoding can be adopted, adding a requirement to declare supportsSecureCoding and to encode objects safely.

In Swift, the method is named encode(with coder: NSCoder) and the decoding initializer is init(coder: NSCoder). The NSCoding protocol remains widely used for legacy APIs and for persisting simple objects, though newer approaches such as Codable are common for modern data interchange.