NSEnumerator

Inherits From:
NSObject

Conforms To:
NSObject (NSObject)

Declared In:
Foundation/NSUtilities.h

Class At A Glance

Purpose

An abstract class whose instances enumerate collections of other objects, such as arrays and dictionaries.

Creation

All creation methods are defined in the collection classes such as NSArray and NSDictionary. These methods contain the word "Enumerator," as in NSArray's objectEnumerator method or NSDictionary's keyEnumerator method.

Commonly Used Methods - nextObject Returns the next object in the collection being enumerated.

Primitive Methods

- nextObject	Returns the next object in the collection being enumerated.

- nextObject

Class Description

NSEnumerator is a simple abstract class whose subclasses enumerate collections of other objects. Collection objects-such as arrays, sets, and dictionaries-provide special NSEnumerator objects with which to enumerate their contents. You send nextObject repeatedly to a newly-created NSEnumerator object to have it return the next object in the original collection. When the collection is exhausted, nil is returned. You can't "reset" an enumerator after it's exhausted its collection. To enumerate a collection again, you need a new enumerator.

Collection classes such as NSArray, NSSet, and NSDictionary include methods that return an enumerator appropriate to the type of collection. For instance, NSArray has two methods that return an NSEnumerator object: objectEnumerator and reverseObjectEnumerator. NSDictionary also has two methods that return an NSEnumerator object: keyEnumerator and objectEnumerator. These methods let you enumerate the contents of an NSDictionary by key or by value, respectively.

Note: It isn't safe to modify a mutable collection while enumerating through it. Like other collection classes, an NSEnumerator retains the collection over which it's enumerating (unless implemented differently by a custom subclass).

Method Types

Getting the objects

- allObjects
- nextObject

Instance Methods

allObjects

- (NSArray *)allObjects

Returns an array of the objects the receiver has yet to enumerate. The array returned by this method does not contain objects that have already been enumerated with previous nextObject messages. Invoking this method exhausts the enumerator's collection so that subsequent invocations of nextObject return nil.

nextObject

- (id)nextObject

Returns the next object from the collection being enumerated. When nextObject returns nil, all objects have been enumerated. The following code illustrates how this works using NSArray:

NSEnumerator *enumerator = [anArray objectEnumerator];
id object;
    
while ((object = [enumerator nextObject])) {
    // do something with object...
}