NSKeyedUnarchiver Class Reference

Inherits from
Conforms to
Framework
/System/Library/Frameworks/Foundation.framework
Availability
Available in OS X v10.2 and later.
Companion guide
Declared in
NSKeyedArchiver.h
Related sample code

Overview

NSKeyedUnarchiver, a concrete subclass of NSCoder, defines methods for decoding a set of named objects (and scalar values) from a keyed archive. Such archives are produced by instances of the NSKeyedArchiver class.

A keyed archive is encoded as a hierarchy of objects. Each object in the hierarchy serves as a namespace into which other objects are encoded. The objects available for decoding are restricted to those that were encoded within the immediate scope of a particular object. Objects encoded elsewhere in the hierarchy, whether higher than, lower than, or parallel to this particular object, are not accessible. In this way, the keys used by a particular object to encode its instance variables need to be unique only within the scope of that object.

If you invoke one of the decode... methods of this class using a key that does not exist in the archive, a non-positive value is returned. This value varies by decoded type. For example, if a key does not exist in an archive, decodeBoolForKey: returns NO, decodeIntForKey: returns 0, and decodeObjectForKey: returns nil.

NSKeyedUnarchiver supports limited type coercion. A value encoded as any type of integer, whether a standard int or an explicit 32-bit or 64-bit integer, can be decoded using any of the integer decode methods. Likewise, a value encoded as a float or double can be decoded as either a float or a double value. If an encoded value is too large to fit within the coerced type, the decoding method throws an NSRangeException. Further, when trying to coerce a value to an incompatible type, for example decoding an int as a float, the decoding method throws an NSInvalidUnarchiveOperationException.

Tasks

Initializing a Keyed Unarchiver

Unarchiving Data

Decoding Data

Managing the Delegate

Managing Class Names

Class Methods

classForClassName:

Returns the class from which NSKeyedUnarchiver instantiates an encoded object with a given class name.

+ (Class)classForClassName:(NSString *)codedName
Parameters
codedName

The ostensible name of a class in an archive.

Return Value

The class from which NSKeyedUnarchiver instantiates an object encoded with the class name codedName. Returns nil if NSKeyedUnarchiver does not have a translation mapping for codedName.

Availability
  • Available in OS X v10.2 and later.
Declared In
NSKeyedArchiver.h

setClass:forClassName:

Adds a class translation mapping to NSKeyedUnarchiver whereby objects encoded with a given class name are decoded as instances of a given class instead.

+ (void)setClass:(Class)cls forClassName:(NSString *)codedName
Parameters
cls

The class with which to replace instances of the class named codedName.

codedName

The ostensible name of a class in an archive.

Discussion

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

Availability
  • Available in OS X v10.2 and later.
Declared In
NSKeyedArchiver.h

unarchiveObjectWithData:

Decodes and returns the object graph previously encoded by NSKeyedArchiver and stored in a given NSData object.

+ (id)unarchiveObjectWithData:(NSData *)data
Parameters
data

An object graph previously encoded by NSKeyedArchiver.

Return Value

The object graph previously encoded by NSKeyedArchiver and stored in data.

Discussion

This method raises an NSInvalidArchiveOperationException if data is not a valid archive.

Availability
  • Available in OS X v10.2 and later.
Declared In
NSKeyedArchiver.h

unarchiveObjectWithFile:

Decodes and returns the object graph previously encoded by NSKeyedArchiver written to the file at a given path.

+ (id)unarchiveObjectWithFile:(NSString *)path
Parameters
path

A path to a file that contains an object graph previously encoded by NSKeyedArchiver.

Return Value

The object graph previously encoded by NSKeyedArchiver written to the file path. Returns nil if there is no file at path.

Discussion

This method raises an NSInvalidArgumentException if the file at path does not contain a valid archive.

Availability
  • Available in OS X v10.2 and later.
Related Sample Code
Declared In
NSKeyedArchiver.h

Instance Methods

classForClassName:

Returns the class from which the receiver instantiates an encoded object with a given class name.

- (Class)classForClassName:(NSString *)codedName
Parameters
codedName

The name of a class.

Return Value

The class from which the receiver instantiates an encoded object with the class name codedName. Returns nil if the receiver does not have a translation mapping for codedName.

Discussion

The class’s separate translation map is not searched.

Availability
  • Available in OS X v10.2 and later.
Declared In
NSKeyedArchiver.h

containsValueForKey:

Returns a Boolean value that indicates whether the archive contains a value for a given key within the current decoding scope.

- (BOOL)containsValueForKey:(NSString *)key
Parameters
key

A key in the archive within the current decoding scope. key must not be nil.

Return Value

YES if the archive contains a value for key within the current decoding scope, otherwise NO.

Availability
  • Available in OS X v10.2 and later.
Declared In
NSKeyedArchiver.h

decodeBoolForKey:

Decodes a Boolean value associated with a given key.

- (BOOL)decodeBoolForKey:(NSString *)key
Parameters
key

A key in the archive within the current decoding scope. key must not be nil.

Return Value

The Boolean value associated with the key key. Returns NO if key does not exist.

Availability
  • Available in OS X v10.2 and later.
See Also
Declared In
NSKeyedArchiver.h

decodeBytesForKey:returnedLength:

Decodes a stream of bytes associated with a given key.

- (const uint8_t *)decodeBytesForKey:(NSString *)key returnedLength:(NSUInteger *)lengthp
Parameters
key

A key in the archive within the current decoding scope. key must not be nil.

lengthp

Upon return, contains the number of bytes returned.

Return Value

The stream of bytes associated with the key key. Returns NULL if key does not exist.

Discussion

The returned value is a pointer to a temporary buffer owned by the receiver. The buffer goes away with the unarchiver, not the containing autoreleasepool block. You must copy the bytes into your own buffer if you need the data to persist beyond the life of the receiver.

Availability
  • Available in OS X v10.2 and later.
See Also
Declared In
NSKeyedArchiver.h

decodeDoubleForKey:

Decodes a double-precision floating-point value associated with a given key.

- (double)decodeDoubleForKey:(NSString *)key
Parameters
key

A key in the archive within the current decoding scope. key must not be nil.

Return Value

The double-precision floating-point value associated with the key key. Returns 0.0 if key does not exist.

Discussion

If the archived value was encoded as single-precision, the type is coerced.

Availability
  • Available in OS X v10.2 and later.
See Also
Declared In
NSKeyedArchiver.h

decodeFloatForKey:

Decodes a single-precision floating-point value associated with a given key.

- (float)decodeFloatForKey:(NSString *)key
Parameters
key

A key in the archive within the current decoding scope. key must not be nil.

Return Value

The single-precision floating-point value associated with the key key. Returns 0.0 if key does not exist.

Discussion

If the archived value was encoded as double precision, the type is coerced, loosing precision. If the archived value is too large for single precision, the method raises an NSRangeException.

Availability
  • Available in OS X v10.2 and later.
See Also
Declared In
NSKeyedArchiver.h

decodeInt32ForKey:

Decodes a 32-bit integer value associated with a given key.

- (int32_t)decodeInt32ForKey:(NSString *)key
Parameters
key

A key in the archive within the current decoding scope. key must not be nil.

Return Value

The 32-bit integer value associated with the key key. Returns 0 if key does not exist.

Discussion

If the archived value was encoded with a different size but is still an integer, the type is coerced. If the archived value is too large to fit into a 32-bit integer, the method raises an NSRangeException.

Availability
  • Available in OS X v10.2 and later.
See Also
Declared In
NSKeyedArchiver.h

decodeInt64ForKey:

Decodes a 64-bit integer value associated with a given key.

- (int64_t)decodeInt64ForKey:(NSString *)key
Parameters
key

A key in the archive within the current decoding scope. key must not be nil.

Return Value

The 64-bit integer value associated with the key key. Returns 0 if key does not exist.

Discussion

If the archived value was encoded with a different size but is still an integer, the type is coerced.

Availability
  • Available in OS X v10.2 and later.
See Also
Declared In
NSKeyedArchiver.h

decodeIntForKey:

Decodes an integer value associated with a given key.

- (int)decodeIntForKey:(NSString *)key
Parameters
key

A key in the archive within the current decoding scope. key must not be nil.

Return Value

The integer value associated with the key key. Returns 0 if key does not exist.

Discussion

If the archived value was encoded with a different size but is still an integer, the type is coerced. If the archived value is too large to fit into the default size for an integer, the method raises an NSRangeException.

Availability
  • Available in OS X v10.2 and later.
See Also
Declared In
NSKeyedArchiver.h

decodeObjectForKey:

Decodes and returns an object associated with a given key.

- (id)decodeObjectForKey:(NSString *)key
Parameters
key

A key in the archive within the current decoding scope. key must not be nil.

Return Value

The object associated with the key key. Returns nil if key does not exist, or if the value for key is nil.

Availability
  • Available in OS X v10.2 and later.
See Also
Related Sample Code
  • With and Without Bindings
Declared In
NSKeyedArchiver.h

delegate

Returns the receiver’s delegate.

- (id<NSKeyedUnarchiverDelegate>)delegate
Return Value

The receiver’s delegate.

Availability
  • Available in OS X v10.2 and later.
Declared In
NSKeyedArchiver.h

finishDecoding

Tells the receiver that you are finished decoding objects.

- (void)finishDecoding
Discussion

Invoking this method allows the receiver to notify its delegate and to perform any final operations on the archive. Once this method is invoked, the receiver cannot decode any further values.

Availability
  • Available in OS X v10.2 and later.
Related Sample Code
  • With and Without Bindings
Declared In
NSKeyedArchiver.h

initForReadingWithData:

Initializes the receiver for decoding an archive previously encoded by NSKeyedArchiver.

- (id)initForReadingWithData:(NSData *)data
Parameters
data

An archive previously encoded by NSKeyedArchiver.

Return Value

An NSKeyedUnarchiver object initialized for for decoding data.

Discussion

When you finish decoding data, you should invoke finishDecoding.

This method throws an exception if data is not a valid archive.

Availability
  • Available in OS X v10.2 and later.
Declared In
NSKeyedArchiver.h

setClass:forClassName:

Adds a class translation mapping to the receiver whereby objects encoded with a given class name are decoded as instances of a given class instead.

- (void)setClass:(Class)cls forClassName:(NSString *)codedName
Parameters
cls

The class with which to replace instances of the class named codedName.

codedName

The ostensible name of a class in an archive.

Discussion

When decoding, the receiver’s translation map overrides any translation that may also be present in the class’s map (see setClass:forClassName:).

Availability
  • Available in OS X v10.2 and later.
Declared In
NSKeyedArchiver.h

setDelegate:

Sets the receiver’s delegate.

- (void)setDelegate:(id<NSKeyedUnarchiverDelegate>)delegate
Parameters
delegate

The delegate for the receiver.

Availability
  • Available in OS X v10.2 and later.
See Also
Declared In
NSKeyedArchiver.h

setRequiresSecureCoding:

Indicates whether the receiver requires all unarchived classes to conform to NSSecureCoding.

- (void)setRequiresSecureCoding:(BOOL)flag
Parameters
flag

YES if the receiver requires NSSecureCoding; NO if not.

Discussion

If you set the receiver to require secure coding, it will throw an exception if you attempt to unarchive a class which does not conform to NSSecureCoding.

The secure coding requirement for NSKeyedUnarchiver is designed to be set once at the top level and remain on. Once enabled, attempting to call setRequiresSecureCoding: with a value of NO will throw an exception. This is to prevent classes from selectively turning secure coding off.

Note that the getter is on the superclass, NSCoder. See NSCoder for more information about secure coding.

Availability
  • Available in OS X v10.8 and later.
Declared In
NSKeyedArchiver.h

Constants

Keyed Unarchiving Exception Names

Names of exceptions that are raised by NSKeyedUnarchiver if there is a problem extracting an archive.

NSString *NSInvalidUnarchiveOperationException;
Constants
NSInvalidUnarchiveOperationException

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

Available in OS X v10.2 and later.

Declared in NSKeyedArchiver.h.