NSArchiver Class Reference

Inherits from
Conforms to
Framework
/System/Library/Frameworks/Foundation.framework
Availability
Available in OS X v10.0 and later.
Companion guide
Declared in
NSArchiver.h
Related sample code

Overview

NSArchiver, a concrete subclass of NSCoder, provides a way to encode objects into an architecture-independent format that can be stored in a file. When you archive a graph of objects, the class information and instance variables for each object are written to the archive. NSArchiver's companion class, NSUnarchiver, decodes the data in an archive and creates a graph of objects equivalent to the original set.

NSArchiver stores the archive data in a mutable data object (NSMutableData). After encoding the objects, you can have the NSArchiver object write this mutable data object immediately to a file, or you can retrieve the mutable data object for some other use.

In OS X v10.2 and later, NSArchiver and NSUnarchiver have been replaced by NSKeyedArchiver and NSKeyedUnarchiver respectively—see Archives and Serializations Programming Guide.

Tasks

Initializing an NSArchiver

Archiving Data

Getting the Archived Data

Substituting Classes or Objects

Class Methods

archivedDataWithRootObject:

Returns a data object containing the encoded form of the object graph whose root object is given.

+ (NSData *)archivedDataWithRootObject:(id)rootObject
Parameters
rootObject

The root object of the object graph to archive.

Return Value

A data object containing the encoded form of the object graph whose root object is rootObject.

Discussion

This method invokes initForWritingWithMutableData: and encodeRootObject: to create a temporary archiver that encodes the object graph.

Availability
  • Available in OS X v10.0 and later.
Declared In
NSArchiver.h

archiveRootObject:toFile:

Creates a temporary instance of NSArchiver and archives an object graph by encoding it into a data object and writing the resulting data object to a specified file.

+ (BOOL)archiveRootObject:(id)rootObject toFile:(NSString *)path
Parameters
rootObject

The root object of the object graph to archive.

path

The location of the the file into which to write the archive.

Return Value

YES if the archive was written successfully, otherwise NO.

Discussion

This convenience method invokes archivedDataWithRootObject: to get the encoded data, and then sends that data object the message writeToFile:atomically:, using path for the first argument and YES for the second.

The archived data should be retrieved from the archive by an NSUnarchiver object.

Availability
  • Available in OS X v10.0 and later.
Declared In
NSArchiver.h

Instance Methods

archiverData

Returns the receiver's archive data.

- (NSMutableData *)archiverData
Return Value

The receiver's archive data.

Discussion

The returned data object is the same one specified as the argument to initForWritingWithMutableData:. It contains whatever data has been encoded thus far by invocations of the various encoding methods. It is safest not to invoke this method until after encodeRootObject: has returned. In other words, although it is possible for a class to invoke this method from within its encodeWithCoder: method, that method must not alter the data.

Availability
  • Available in OS X v10.0 and later.
Related Sample Code
Declared In
NSArchiver.h

classNameEncodedForTrueClassName:

Returns the name of the class used to archive instances of the class with a given true name.

- (NSString *)classNameEncodedForTrueClassName:(NSString *)trueName
Parameters
trueName

The real name of an encoded class.

Return Value

The name of the class used to archive instances of the class trueName.

Availability
  • Available in OS X v10.0 and later.
Declared In
NSArchiver.h

encodeClassName:intoClassName:

Encodes a substitute name for the class with a given true name.

- (void)encodeClassName:(NSString *)trueName intoClassName:(NSString *)inArchiveName
Parameters
trueName

The real name of a class in the object graph being archived.

inArchiveName

The name of the class to use in the archive in place of trueName.

Discussion

Any subsequently encountered objects of class trueName are archived as instances of class inArchiveName. It is safest not to invoke this method during the archiving process (that is, within an encodeWithCoder: method). Instead, invoke it before encodeRootObject:.

Availability
  • Available in OS X v10.0 and later.
Declared In
NSArchiver.h

encodeConditionalObject:

Conditionally archives a given object.

- (void)encodeConditionalObject:(id)object
Parameters
object

The object to archive.

Discussion

This method overrides the superclass implementation to allow object to be encoded only if it is also encoded unconditionally by another object in the object graph. Conditional encoding lets you encode one part of a graph detached from the rest. (See Archives and Serializations Programming Guide for more information.)

This method should be invoked only from within an encodeWithCoder: method. If object is nil, the NSArchiver object encodes it unconditionally as nil. This method raises an NSInvalidArgumentException if no root object has been encoded.

Availability
  • Available in OS X v10.0 and later.
Declared In
NSArchiver.h

encodeRootObject:

Archives a given object along with all the objects to which it is connected.

- (void)encodeRootObject:(id)rootObject
Parameters
rootObject

The root object of the object graph to archive.

Discussion

If any object is encountered more than once while traversing the graph, it is encoded only once, but the multiple references to it are stored. (See Archives and Serializations Programming Guide for more information.)

This message must not be sent more than once to a given NSArchiver object; an NSInvalidArgumentException is raised if a root object has already been encoded. If you need to encode multiple object graphs, therefore, don’t attempt to reuse an NSArchiver instance; instead, create a new one for each graph.

Availability
  • Available in OS X v10.0 and later.
Declared In
NSArchiver.h

initForWritingWithMutableData:

Returns an archiver, initialized to encode stream and version information into a given mutable data object.

- (id)initForWritingWithMutableData:(NSMutableData *)data
Parameters
data

The mutable data object into which to write the archive. This value must not be nil.

Return Value

An archiver object, initialized to encode stream and version information into data.

Discussion

Raises an NSInvalidArgumentException if data is nil.

Availability
  • Available in OS X v10.0 and later.
Declared In
NSArchiver.h

replaceObject:withObject:

Causes the receiver to treat subsequent requests to encode a given object as though they were requests to encode another given object.

- (void)replaceObject:(id)object withObject:(id)newObject
Parameters
object

An object in the object graph being archived.

newObject

The object with which to replace object in the archive.

Discussion

Both object and newObject must be valid objects.

Availability
  • Available in OS X v10.0 and later.
Declared In
NSArchiver.h

Constants

Archiving Exception Names

Raised by NSArchiver if there are problems initializing or encoding.

extern NSString *NSInconsistentArchiveException;
Constants
NSInconsistentArchiveException

The name of an exception raised by NSArchiver if there are problems initializing or encoding.

Available in OS X v10.0 and later.

Declared in NSArchiver.h.

Declared In
NSArchiver.h