NSKeyedUnarchiver

NSKeyedUnarchiver is a class in the Apple Foundation framework used to deserialize objects that were previously encoded with NSKeyedArchiver. It supports decoding objects that implement NSCoding (Objective-C) or NSSecureCoding (Swift), allowing structured data to be reconstructed from archived representations.

Basic usage typically involves providing a data source to a decoding API. In modern Swift, the common entry point is NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(_:) which takes a Data instance containing the archived payload and returns the top-level object, potentially throwing an error. The caller must then cast the result to the expected type. The older API NSKeyedUnarchiver.unarchiveObject(with:) exists for compatibility but is deprecated in favor of the top-level object variant and explicit error handling.

Security considerations are important with keyed archiving. To mitigate risks such as object substitution attacks, classes intended for decoding should conform to NSSecureCoding and implement supportsSecureCoding and the required init(coder:). When decoding, enable secure coding by configuring the NSKeyedUnarchiver (for example, setting requiresSecureCoding = true on an unarchiver instance) and ensure that only classes that support secure coding are allowed. If data was archived without secure coding, decoding may fail or be unsafe.

Notes and limitations include the need for the original class definitions during decoding; changes to class implementations or missing classes can cause decoding to fail. Versioning strategies and explicit class constraints are commonly used to maintain compatibility. NSKeyedUnarchiver works with data, streams, or URLs, but successful decoding depends on matching the archived structure with the receiving app’s available class definitions.

See also NSKeyedArchiver and NSSecureCoding.