voidencodeWithCoderNSCoder

Void encodeWithCoder NSCoding method overview

encodeWithCoder: is the Objective-C instance method used to save an object's state into a coder, making the object eligible for archiving and persistence. It is a required method of the NSCoding protocol, and it is paired with initWithCoder: to support round-trip encoding and decoding. In practical terms, an object implements this method to write its properties into the provided NSCoder, so that later it can be restored.

Signature and usage

In Objective-C, the method is declared as - (void)encodeWithCoder:(NSCoder *)coder;. When an object is archived with mechanisms such as NSKeyedArchiver, the runtime calls encodeWithCoder: on the object, and the object's properties are encoded into the coder with specific keys. The corresponding decoding occurs in initWithCoder:, where values are retrieved from the coder using the matching keys.

Implementation pattern

A typical implementation encodes each relevant property, using appropriate coder methods such as encodeObject:forKey:, encodeInteger:forKey:, encodeBool:forKey:, or encodeDouble:forKey:. Keys should be consistent between encoding and decoding. If the class inherits from a superclass that also conforms to NSCoding, the implementation may call [super encodeWithCoder:coder]; to ensure the superclass state is preserved.

Decoding and safety

The complementary implementation in initWithCoder: retrieves values with decodeObjectForKey:, decodeIntegerForKey:, decodeBoolForKey:, etc., and assigns them to the object's properties. If secure coding is desired, the class may adopt NSSecureCoding and implement +supportsSecureCoding, using decodeObjectOfClass:forKey: and related methods to enforce type safety.

Relation to archiving APIs

encodeWithCoder: is used with keyed archivers such as NSKeyedArchiver and NSKeyedUnarchiver, enabling robust persistence of complex object graphs. Proper implementation ensures reliable restoration of object state across app launches, transfers, or storage.