NSMutableDictionary is the mutable version of NSDictionary.
Like NSDictionary (nsdictionary), it is a subclass of NSObject (nsobject), that allows you to have a collection of objects, but instead of having them stored in an array retrievable by their index, they are stored as a key-value pair. Each object stored in an NSDictionary can be retrieved by a unique key assigned to it. Keys have to be unique and can be any object as long as they adopt the NSCopying protocol – they are usually an instance of NSString (nsstring).
Neither a key nor the object paired with it can be nil, however, you may use NSNull for storing null objects.
If two objects are stored with the same key, the first one is released, and the last one is stored.
When using key-value coding, the key must be a string.
When using key-object coding, the key is copied using copyWithZone: and it must conform to the NSCopying protocol. This object is retained, rather than copy.
NSMutableDictionary gives you the ability to modify this set of key-object paired collection without having to empty it and refill it again as a whole set. The following methods are for this purpose:
Adding Entries to a Mutable Dictionary
– setObject:forKey:
– setValue:forKey:
– addEntriesFromDictionary:
– setDictionary:
Removing Entries From a Mutable Dictionary
– removeObjectForKey:
– removeAllObjects
– removeObjectsForKeys:
