This class and its subclasses store key-value pairs,
where the key and the value are objects. A great many
utility methods for working with dictionaries are
provided as part of this class, including the
ability to retrieve multiple entries
simultaneously, obtain sorted contents, and
read/write from/to a serialized representation.
The keys are copied and values are retained by the
implementation, and both are released when
either their entry is dropped or the entire
dictionary is deallocated. As in the OS X
implementation, keys must therefore
implement the
<NSCopying>
protocol.
Objects of this class are immutable. For a
mutable version, use the
NSMutableDictionary
subclass.
The basic functionality in
NSDictionary is similar to that in
Java's HashMap, and like that class
it includes no locking code and is not thread-safe.
If the contents will be modified and accessed from
multiple threads you should enclose critical
operations within locks (see
NSLock
).
Returns a dictionary created using the given
objects and keys. The two
arrays must have the same length. The n th element
of the objects array is associated with the n
th element of the keys array.
Returns a dictionary created using the given
objects and keys. The two
arrays must have the same size. The n th element of
the objects array is associated with the n
th element of the keys array.
Returns a dictionary created using the list given
as argument. The list is alternately composed of objects
and keys and terminated by nil. Thus, the
list's length must be even, followed by
nil.
Returns the receiver as a text property list in the
traditional format. See
[NSString -propertyList]
for details. If locale is
nil, no formatting is done, otherwise
entries are formatted according to the
locale, and indented according to
level. Unless locale is
nil, a level of zero indents
items by four spaces, while a level of one
indents them by a tab. If the keys in the
dictionary respond to
[NSString -compare:]
, the items are listed by key in ascending order. If not,
the order in which the items are listed is undefined.
In MacOS-X class clusters do not have designated
initialisers, and there is a general rule
that -init
is
treated as the designated initialiser of the
class cluster, but that other intitialisers may not
work s expected an would need to be individually
overridden in any subclass.
GNUstep tries to make it easier to subclass a
class cluster, by making class clusters follow the
same convention as normal classes, so the designated
initialiser is the richest
initialiser. This means that all other
initialisers call the documented designated
initialiser (which calls
-init
only for MacOS-X compatibility), and anyone writing
a subclass only needs to override that one initialiser
in order to have all the other ones work.
For MacOS-X compatibility, you may also need to
override various other initialisers. Exactly
which ones, you will need to determine by trial on
a MacOS-X system... and may vary between releases of
MacOS-X. So to be safe, on MacOS-X you probably
need to re-implement all the class cluster
initialisers you might use in conjunction
with your subclass.
Initialises the dictionary with the contents
of the specified file, which must contain a dictionary
in property-list format.
In GNUstep, the property-list format may be either the
OpenStep format (ASCII data), or the MacOS-X
format (UTF-8 XML data)... this method will
recognise which it is.
If there is a failure to load the file for any reason,
the receiver will be released and the method will
return nil.
Initialises the dictionary with the contents
of the specified URL, which must contain a dictionary
in property-list format.
In GNUstep, the property-list format may be either the
OpenStep format (ASCII data), or the MacOS-X
format (UTF-8 XML data)... this method will
recognise which it is.
If there is a failure to load the URL for any reason,
the receiver will be released and the method will
return nil.
Initialise dictionary with the keys and values
of otherDictionary. If the shouldCopy flag is
YES then the values are copied into the
newly initialised dictionary, otherwise they are
simply retained, on the assumption that it is safe
to retain the keys from another dictionary since that
other dictionary mwill have copied the
keys originally to ensure that they are immutable.
Initialises a dictionary created using the
given objects and keys. The two
arrays must have the same size. The n th element of
the objects array is associated with the n
th element of the keys array.
This is a designated initialiser for the class.
Subclasses must override this method.
Initializes contents to the given
objects and keys. The two
arrays must have the same size. The n th element of
the objects array is associated with the n
th element of the keys array. Calls
-init
(which does nothing but maintain MacOS-X
compatibility), and needs to be
re-implemented in subclasses in order to
have all other initialisers work.
Initialises a dictionary created using the list
given as argument. The list is alternately composed
of objects and keys and terminated by nil.
Thus, the list's length must be even, followed by
nil.
Two dictionaries are equal if they each hold the same
number of entries, each key in one
isEqual to a key in the
other, and, for a given key, the
corresponding value objects also satisfy
isEqual.
Returns ordered array of the keys sorted according
to the values they correspond to. To sort the values, a
message with selector comp is send to
each value with another value as argument, as in
[a comp: b]. The comp method
should return NSOrderedSame,
NSOrderedAscending, or
NSOrderedDescending as appropriate.
Multiple version of
-objectForKey:
. Objects for each key in keys are looked up
and placed into return array in same order. For each
key that has no corresponding value in this dictionary,
marker is put into the array in its place.
Default implementation for this class is to return
the value stored in the dictionary under the specified
key, or nil if there is no
value. However, if the key begins
with '@' that character is stripped from it and the
superclass implementation of the method is used.
Writes the contents of the dictionary to the file
specified by path. The file contents
will be in property-list format... under GNUstep
this is either OpenStep style (ASCII characters
using \U hexadecimal escape sequences for unicode),
or MacOS-X style (XML in the UTF8 character set).
If the useAuxiliaryFile flag is
YES, the file write operation is
atomic... the data is written to a temporary file,
which is then renamed to the actual file name.
If the conversion of data into the correct
property-list format fails or the write
operation fails, the method returns
NO, otherwise it returns
YES.
NB. The fact that the file is in property-list format
does not necessarily mean that it can be used to
reconstruct the dictionary using the
-initWithContentsOfFile:
method. If the original dictionary contains
non-property-list objects, the
descriptions of those objects will have been
written, and reading in the file as a
property-list will result in a new
dictionary containing the string descriptions.
Writes the contents of the dictionary to the
specified url. This functions just
like
-writeToFile:atomically:
except that the output may be written to any URL,
not just a local file.
Returns an empty dictionary with memory
preallocated for given number of entries.
Although memory space will be grown as needed when
entries are added, this can avoid the
reallocate-and-copy process if the size
of the ultimate contents is known in advance.
Merges information from otherDictionary
into the receiver. If a key exists in both
dictionaries, the value from
otherDictionary replaces that which was
originally in the receiver.
This is a designated initialiser for the class.
Subclasses must override this method.
Initializes an empty dictionary with memory
preallocated for given number of entries.
Although memory space will be grown as needed when
entries are added, this can avoid the
reallocate-and-copy process if the size
of the ultimate contents is known in advance.
Calls -init
(which does nothing but maintain MacOS-X
compatibility), and needs to be
re-implemented in subclasses in order to
have all other initialisers work.
Removes the object with the specified key from the
receiver. This method is primitive. Remove
key-value mapping for given key aKey.
No error if there is no mapping for the key. A warning
will be generated if aKey is
nil.
Remove entries specified by the given
keyArray. No error is generated if no
mapping exists for a key or one is nil
, although a console warning is produced in the latter
case.
Adds entry for aKey, mapping to
anObject. If either is nil,
an exception is raised. If aKey already in
dictionary, the value it maps to is silently
replaced. The value anObject is
retained, but aKey is copied (because
a dictionary key must be immutable) and must therefore
implement the
<NSCopying>
protocol.)