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NSEnumerator


Inherits from: NSObject
Package: com.apple.yellow.foundation

Class at a Glance


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

Principal Attributes


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



nextElement Returns the next object in the collection being enumerated.

Primitive Methods



nextElement Returns the next object in the collection being enumerated.




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 nextElement repeatedly to a newly-created NSEnumerator object to have it return the next object in the original collection. When the collection is exhausted, null 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.



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
nextElement


Instance Methods



getObjCEnumerator

public int getObjCEnumerator()



hasMoreElements

public boolean hasMoreElements()



nextElement

public Object nextElement()

Returns the next object from the collection being enumerated. When nextElement returns null, all objects have been enumerated.


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It isn't safe to modify a mutable collection while enumerating through it.