Objective-C Language NSDictionary


  • @{ key: value, ... }

  • [NSDictionary dictionaryWithObjectsAndKeys: value, key, ..., nil];

  • dict[key] = value;

  • id value = dict[key];


The NSDictionary class declares the programmatic interface to objects that manage immutable associations of keys and values. Use this class or its subclass NSMutableDictionary when you need a convenient and efficient way to retrieve data associated with an arbitrary key. NSDictionary creates static dictionaries, and NSMutableDictionary creates dynamic dictionaries. (For convenience, the term dictionary refers to any instance of one of these classes without specifying its exact class membership.)

A key-value pair within a dictionary is called an entry. Each entry consists of one object that represents the key and a second object that is that key’s value. Within a dictionary, the keys are unique. That is, no two keys in a single dictionary are equal (as determined by isEqual:). In general, a key can be any object (provided that it conforms to the NSCopying protocol—see below), but note that when using key-value coding the key must be a string (see Key-Value Coding Fundamentals). Neither a key nor a value can be nil; if you need to represent a null value in a dictionary, you should use NSNull.

NSDictionary is “toll-free bridged” with its Core Foundation counterpart, CFDictionaryRef. See Toll-Free Bridging for more information on toll-free bridging.