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NSKeyedArchiver Class Reference

Overview

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

A keyed archive differs from a non-keyed archive in that all the objects and values encoded into the archive are given names, or keys. When decoding a non-keyed archive, values have to be decoded in the same order in which they were encoded. When decoding a keyed archive, because values are requested by name, values can be decoded out of sequence or not at all. Keyed archives, therefore, provide better support for forward and backward compatibility.

The keys given to encoded values must be unique only within the scope of the current object being encoded. A keyed archive is hierarchical, so the keys used by object A to encode its instance variables do not conflict with the keys used by object B, even if A and B are instances of the same class. Within a single object, however, the keys used by a subclass can conflict with keys used in its superclasses.

An NSArchiver object can write the archive data to a file or to a mutable-data object (an instance of NSMutableData) that you provide.

Tasks

Initializing an NSKeyedArchiver Object

• – initForWritingWithMutableData:

Archiving Data

• + archivedDataWithRootObject:
• + archiveRootObject:toFile:
• – finishEncoding
• – outputFormat
• – setOutputFormat:

Encoding Data and Objects

• – archiver:didEncodeObject:  delegate method
• – archiverDidFinish:  delegate method
• – archiver:willEncodeObject:  delegate method
• – archiverWillFinish:  delegate method
• – archiver:willReplaceObject:withObject:  delegate method
• – encodeBool:forKey:
• – encodeBytes:length:forKey:
• – encodeConditionalObject:forKey:
• – encodeDouble:forKey:
• – encodeFloat:forKey:
• – encodeInt:forKey:
• – encodeInt32:forKey:
• – encodeInt64:forKey:
• – encodeObject:forKey:

Managing Delegates

• – delegate
• – setDelegate:

Managing Classes and Class Names

• + setClassName:forClass:
• + classNameForClass:
• – setClassName:forClass:
• – classNameForClass:

Class Methods

archivedDataWithRootObject:

Returns an NSData object containing the encoded form of the object graph whose root object is given.

+ (NSData *)archivedDataWithRootObject:(id)rootObject

Parameters

rootObject

The root of the object graph to archive.

Return Value

An NSData object containing the encoded form of the object graph whose root object is rootObject. The format of the archive is NSPropertyListBinaryFormat_v1_0.

Availability

• Available in Mac OS X v10.2 and later.

Related Sample Code

• CoreRecipes
• CustomAtomicStoreSubclass
• iSpend
• QTQuartzPlayer
• Squiggles

Declared In

NSKeyedArchiver.h

archiveRootObject:toFile:

Archives an object graph rooted at a given object by encoding it into a data object then atomically writes the resulting data object to a file at a given path, and returns a Boolean value that indicates whether the operation was successful.

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

Parameters

rootObject

The root of the object graph to archive.

path

The path of the file in which to write the archive.

Return Value

YES if the operation was successful, otherwise NO.

Discussion

The format of the archive is NSPropertyListBinaryFormat_v1_0.

Availability

• Available in Mac OS X v10.2 and later.

Declared In

NSKeyedArchiver.h

classNameForClass:

Returns the class name with which NSKeyedArchiver encodes instances of a given class.

+ (NSString *)classNameForClass:(Class)cls

Parameters

cls

The class for which to determine the translation mapping.

Return Value

The class name with which NSKeyedArchiver encodes instances of cls. Returns nil if NSKeyedArchiver does not have a translation mapping for cls.

Availability

• Available in Mac OS X v10.2 and later.

See Also

• + setClassName:forClass:
• – classNameForClass:

Declared In

NSKeyedArchiver.h

setClassName:forClass:

Adds a class translation mapping to NSKeyedArchiver whereby instances of of a given class are encoded with a given class name instead of their real class names.

+ (void)setClassName:(NSString *)codedName forClass:(Class)cls

Parameters

codedName

The name of the class that NSKeyedArchiver uses in place of cls.

cls

The class for which to set up a translation mapping.

Discussion

When encoding, the class’s translation mapping is used only if no translation is found first in an instance’s separate translation map.

Availability

• Available in Mac OS X v10.2 and later.

See Also

• + classNameForClass:
• – setClassName:forClass:

Declared In

NSKeyedArchiver.h

Instance Methods

classNameForClass:

Returns the class name with which the receiver encodes instances of a given class.

- (NSString *)classNameForClass:(Class)cls

Parameters

cls

The class for which to determine the translation mapping.

Return Value

The class name with which the receiver encodes instances of cls. Returns nil if the receiver does not have a translation mapping for cls. The class’s separate translation map is not searched.

Availability

• Available in Mac OS X v10.2 and later.

See Also

• – setClassName:forClass:
• + classNameForClass:

Declared In

NSKeyedArchiver.h

delegate

Returns the receiver’s delegate.

- (id)delegate

Return Value

The receiver's delegate.

Availability

• Available in Mac OS X v10.2 and later.

See Also

• – setDelegate:

Declared In

NSKeyedArchiver.h

encodeBool:forKey:

Encodes a given Boolean value and associates it with a given key.

- (void)encodeBool:(BOOL)boolv forKey:(NSString *)key

Parameters

boolv

The value to encode.

key

The key with which to associate boolv. This value must not be nil.

Availability

• Available in Mac OS X v10.2 and later.

See Also

• decodeBoolForKey: (NSKeyedUnarchiver)

Declared In

NSKeyedArchiver.h

encodeBytes:length:forKey:

Encodes a given number of bytes from a given C array of bytes and associates them with the a given key.

- (void)encodeBytes:(const uint8_t *)bytesp length:(NSUInteger)lenv forKey:(NSString *)key

Parameters

bytesp

A C array of bytes to encode.

lenv

The number of bytes from bytesp to encode.

key

The key with which to associate the encoded value. This value must not be nil.

Availability

• Available in Mac OS X v10.2 and later.

See Also

• decodeBytesForKey:returnedLength: (NSKeyedUnarchiver)

Declared In

NSKeyedArchiver.h

encodeConditionalObject:forKey:

Encodes a reference to a given object and associates it with a given key only if it has been unconditionally encoded elsewhere in the archive with encodeObject:forKey:.

- (void)encodeConditionalObject:(id)objv forKey:(NSString *)key

Parameters

objv

The object to encode.

key

The key with which to associate the encoded value. This value must not be nil.

Availability

• Available in Mac OS X v10.2 and later.

Declared In

NSKeyedArchiver.h

encodeDouble:forKey:

Encodes a given double value and associates it with a given key.

- (void)encodeDouble:(double)realv forKey:(NSString *)key

Parameters

realv

The value to encode.

key

The key with which to associate realv. This value must not be nil.

Availability

• Available in Mac OS X v10.2 and later.

See Also

• decodeDoubleForKey: (NSKeyedUnarchiver)
• decodeFloatForKey: (NSKeyedUnarchiver)

Declared In

NSKeyedArchiver.h

encodeFloat:forKey:

Encodes a given float value and associates it with a given key.

- (void)encodeFloat:(float)realv forKey:(NSString *)key

Parameters

realv

The value to encode.

key

The key with which to associate realv. This value must not be nil.

Availability

• Available in Mac OS X v10.2 and later.

See Also

• decodeFloatForKey: (NSKeyedUnarchiver)
• decodeDoubleForKey: (NSKeyedUnarchiver)

Declared In

NSKeyedArchiver.h

encodeInt32:forKey:

Encodes a given 32-bit integer value and associates it with a given key.

- (void)encodeInt32:(int32_t)intv forKey:(NSString *)key

Parameters

intv

The value to encode.

key

The key with which to associate intv. This value must not be nil.

Availability

• Available in Mac OS X v10.2 and later.

See Also

• decodeInt32ForKey: (NSKeyedUnarchiver)

Declared In

NSKeyedArchiver.h

encodeInt64:forKey:

Encodes a given 64-bit integer value and associates it with a given key.

- (void)encodeInt64:(int64_t)intv forKey:(NSString *)key

Parameters

intv

The value to encode.

key

The key with which to associate intv. This value must not be nil.

Availability

• Available in Mac OS X v10.2 and later.

See Also

• decodeInt64ForKey: (NSKeyedUnarchiver)

Declared In

NSKeyedArchiver.h

encodeInt:forKey:

Encodes a given int value and associates it with a given key.

- (void)encodeInt:(int)intv forKey:(NSString *)key

Parameters

intv

The value to encode.

key

The key with which to associate intv. This value must not be nil.

Availability

• Available in Mac OS X v10.2 and later.

See Also

• decodeIntForKey: (NSKeyedUnarchiver)

Declared In

NSKeyedArchiver.h

encodeObject:forKey:

Encodes a given object and associates it with a given key.

- (void)encodeObject:(id)objv forKey:(NSString *)key

Parameters

objv

The value to encode. This value may be nil.

key

The key with which to associate objv. This value must not be nil.

Availability

• Available in Mac OS X v10.2 and later.

See Also

• decodeObjectForKey: (NSKeyedUnarchiver)

Declared In

NSKeyedArchiver.h

finishEncoding

Instructs the receiver to construct the final data stream.

- (void)finishEncoding

Discussion

No more values can be encoded after this method is called. You must call this method when finished.

Availability

• Available in Mac OS X v10.2 and later.

See Also

• – initForWritingWithMutableData:

Declared In

NSKeyedArchiver.h

initForWritingWithMutableData:

Returns the receiver, initialized for encoding an archive into a given a mutable-data object.

- (id)initForWritingWithMutableData:(NSMutableData *)data

Parameters

data

The mutable-data object into which the archive is written.

Return Value

The receiver, initialized for encoding an archive into data.

Discussion

When you finish encoding data, you must invoke finishEncoding at which point data is filled. The format of the receiver is NSPropertyListBinaryFormat_v1_0.

Availability

• Available in Mac OS X v10.2 and later.

Declared In

NSKeyedArchiver.h

outputFormat

Returns the format in which the receiver encodes its data.

- (NSPropertyListFormat)outputFormat

Return Value

The format in which the receiver encodes its data. The available formats are NSPropertyListXMLFormat_v1_0 and NSPropertyListBinaryFormat_v1_0.

Availability

• Available in Mac OS X v10.2 and later.

See Also

• – setOutputFormat:

Declared In

NSKeyedArchiver.h

setClassName:forClass:

Adds a class translation mapping to the receiver whereby instances of of a given class are encoded with a given class name instead of their real class names.

- (void)setClassName:(NSString *)codedName forClass:(Class)cls

Parameters

codedName

The name of the class that the receiver uses uses in place of cls.

cls

The class for which to set up a translation mapping.

Discussion

When encoding, the receiver’s translation map overrides any translation that may also be present in the class’s map.

Availability

• Available in Mac OS X v10.2 and later.

See Also

• – classNameForClass:
• + setClassName:forClass:

Declared In

NSKeyedArchiver.h

setDelegate:

Sets the delegate for the receiver.

- (void)setDelegate:(id)delegate

Parameters

delegate

The delegate for the receiver.

Availability

• Available in Mac OS X v10.2 and later.

See Also

• – delegate

Declared In

NSKeyedArchiver.h

setOutputFormat:

Sets the format in which the receiver encodes its data.

- (void)setOutputFormat:(NSPropertyListFormat)format

Parameters

format

The format in which the receiver encodes its data. format can be NSPropertyListXMLFormat_v1_0 or NSPropertyListBinaryFormat_v1_0.

Availability

• Available in Mac OS X v10.2 and later.

See Also

• – outputFormat

Declared In

NSKeyedArchiver.h

Delegate Methods

archiver:didEncodeObject:

Informs the delegate that a given object has been encoded.

- (void)archiver:(NSKeyedArchiver *)archiver didEncodeObject:(id)object

Parameters

archiver

The archiver that sent the message.

object

The object that has been encoded. object may be nil.

Discussion

The delegate might restore some state it had modified previously, or use this opportunity to keep track of the objects that are encoded.

This method is not called for conditional objects until they are actually encoded (if ever).

Availability

• Available in Mac OS X v10.2 and later.

Declared In

NSKeyedArchiver.h

archiver:willEncodeObject:

Informs the delegate that object is about to be encoded.

- (id)archiver:(NSKeyedArchiver *)archiver willEncodeObject:(id)object

Parameters

archiver

The archiver that sent the message.

object

The object that is about to be encoded. This value is never nil.

Return Value

Either object or a different object to be encoded in its stead. The delegate can also modify the coder state. If the delegate returns nil, nil is encoded.

Discussion

This method is called after the original object may have replaced itself with replacementObjectForKeyedArchiver:.

This method is called whether or not the object is being encoded conditionally.

This method is not called for an object once a replacement mapping has been set up for that object (either explicitly, or because the object has previously been encoded). This method is also not called when nil is about to be encoded.

Availability

• Available in Mac OS X v10.2 and later.

Declared In

NSKeyedArchiver.h

archiver:willReplaceObject:withObject:

Informs the delegate that one given object is being substituted for another given object.

- (void)archiver:(NSKeyedArchiver *)archiver willReplaceObject:(id)object withObject:(id)newObject

Parameters

archiver

The archiver that sent the message.

object

The object being replaced in the archive.

newObject

The object replacing object in the archive.

Discussion

This method is called even when the delegate itself is doing, or has done, the substitution. The delegate may use this method if it is keeping track of the encoded or decoded objects.

Availability

• Available in Mac OS X v10.2 and later.

Declared In

NSKeyedArchiver.h

archiverDidFinish:

Notifies the delegate that encoding has finished.

- (void)archiverDidFinish:(NSKeyedArchiver *)archiver

Parameters

archiver

The archiver that sent the message.

Availability

• Available in Mac OS X v10.2 and later.

Declared In

NSKeyedArchiver.h

archiverWillFinish:

Notifies the delegate that encoding is about to finish.

- (void)archiverWillFinish:(NSKeyedArchiver *)archiver

Parameters

archiver

The archiver that sent the message.

Availability

• Available in Mac OS X v10.2 and later.

Declared In

NSKeyedArchiver.h

Constants

Keyed Archiving Exception Names

Names of exceptions that are raised by NSKeyedArchiver if there is a problem creating an archive.

extern NSString *NSInvalidArchiveOperationException;

Constants

NSInvalidArchiveOperationException

The name of the exception raised by NSKeyedArchiver if there is a problem creating an archive.

Available in Mac OS X v10.2 and later.

Declared in NSKeyedArchiver.h.

Declared In

NSKeyedArchiver.h

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