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NSArray Class Reference

Inherits from
Conforms to
Framework
/System/Library/Frameworks/Foundation.framework
Availability
Available in Mac OS X v10.0 and later.
Declared in
NSArray.h
NSKeyValueCoding.h
NSKeyValueObserving.h
NSPathUtilities.h
NSPredicate.h
NSSortDescriptor.h
Companion guides
Related sample code

Overview

NSArray and its subclass NSMutableArray manage collections of objects called arrays. NSArray creates static arrays, and NSMutableArray creates dynamic arrays.

The NSArray and NSMutableArray classes adopt the NSCopying and NSMutableCopying protocols, making it convenient to convert an array of one type to the other.

NSArray and NSMutableArray are part of a class cluster, so arrays are not actual instances of the NSArray or NSMutableArray classes but of one of their private subclasses. Although an array’s class is private, its interface is public, as declared by these abstract superclasses, NSArray and NSMutableArray.

NSArray’s two primitive methods—count and objectAtIndex:—provide the basis for all other methods in its interface. The count method returns the number of elements in the array; objectAtIndex: gives you access to the array elements by index, with index values starting at 0.

The methods objectEnumerator and reverseObjectEnumerator also grant sequential access to the elements of the array, differing only in the direction of travel through the elements. These methods are provided so that arrays can be traversed in a manner similar to that used for objects of other collection classes, such as NSDictionary. See the objectEnumerator method description for a code excerpt that shows how to use these methods to access the elements of an array. In Mac OS X v10.5 and later, it is more efficient to use the fast enumeration protocol (see NSFastEnumeration).

NSArray provides methods for querying the elements of the array. The indexOfObject: method searches the array for the object that matches its argument. To determine whether the search is successful, each element of the array is sent an isEqual: message, as declared in the NSObject protocol. Another method, indexOfObjectIdenticalTo:, is provided for the less common case of determining whether a specific object is present in the array. The indexOfObjectIdenticalTo: method tests each element in the array to see whether its id matches that of the argument.

NSArray’s filteredArrayUsingPredicate: method allows you to create a new array from an existing array filtered using a predicate (see Predicate Programming Guide).

NSArray’s makeObjectsPerformSelector: and makeObjectsPerformSelector:withObject: methods let you send messages to all objects in the array. To act on the array as a whole, a variety of other methods are defined. You can create a sorted version of the array (sortedArrayUsingSelector: and sortedArrayUsingFunction:context:, extract a subset of the array (subarrayWithRange:), or concatenate the elements of an array of NSString objects into a single string (componentsJoinedByString:). In addition, you can compare two arrays using the isEqualToArray: and firstObjectCommonWithArray: methods. Finally, you can create new arrays that contain the objects in an existing array and one or more additional objects with arrayByAddingObject: and arrayByAddingObjectsFromArray:.

Arrays maintain strong references to their contents—in a managed memory environment, each object receives a retain message before its id is added to the array and a release message when it is removed from the array or when the array is deallocated. If you want a collection with different object ownership semantics, consider using CFArray Reference, NSPointerArray, or NSHashTable instead.

NSArray is “toll-free bridged” with its Core Foundation counterpart, CFArray Reference. What this means is that the Core Foundation type is interchangeable in function or method calls with the bridged Foundation object, providing you cast one type to the other. Therefore, in an API where you see an NSArray * parameter, you can pass in a CFArrayRef, and in an API where you see a CFArrayRef parameter, you can pass in an NSArray instance. This arrangement also applies to your concrete subclasses of NSArray. See Carbon-Cocoa Integration Guide for more information on toll-free bridging.

Subclassing Notes

Most developers would not have any reason to subclass NSArray. The class does well what it is designed to do—maintain an ordered collection of objects. But there are situations where a custom NSArray object might come in handy. Here are a few possibilities:

Methods to Override

Any subclass of NSArray must override the primitive instance methods count and objectAtIndex:. These methods must operate on the backing store that you provide for the elements of the collection. For this backing store you can use a static array, a standard NSArray object, or some other data type or mechanism. You may also choose to override, partially or fully, any other NSArray method for which you want to provide an alternative implementation.

You might want to implement an initializer for your subclass that is suited to the backing store that the subclass is managing. The NSArray class does not have a designated initializer, so your initializer need only invoke the init method of super. The NSArray class adopts the NSCopying, NSMutableCopying, and NSCoding protocols; if you want instances of your own custom subclass created from copying or coding, override the methods in these protocols.

Remember that NSArray is the public interface for a class cluster and what this entails for your subclass. The primitive methods of NSArray do not include any designated initializers. This means that you must provide the storage for your subclass and implement the primitive methods that directly act on that storage.

Special Considerations

In most cases your custom NSArray class should conform to Cocoa’s object-ownership conventions. Thus you must send retain to each object that you add to your collection and release to each object that you remove from the collection. Of course, if the reason for subclassing NSArray is to implement object-retention behavior different from the norm (for example, a non-retaining array), then you can ignore this requirement.

Alternatives to Subclassing

Before making a custom class of NSArray, investigate NSPointerArray, NSHashTable, and the corresponding Core Foundation type, CFArray Reference. Because NSArray and CFArray are “toll-free bridged,” you can substitute a CFArray object for a NSArray object in your code (with appropriate casting). Although they are corresponding types, CFArray and NSArray do not have identical interfaces or implementations, and you can sometimes do things with CFArray that you cannot easily do with NSArray. For example, CFArray provides a set of callbacks, some of which are for implementing custom retain-release behavior. If you specify NULL implementations for these callbacks, you can easily get a non-retaining array.

If the behavior you want to add supplements that of the existing class, you could write a category on NSArray. Keep in mind, however, that this category will be in effect for all instances of NSArray that you use, and this might have unintended consequences.

Adopted Protocols

NSCoding
NSCopying
NSMutableCopying

Tasks

Creating an Array

Initializing an Array

Querying an Array

Sending Messages to Elements

Comparing Arrays

Deriving New Arrays

Sorting

Working with String Elements

Creating a Description

Collecting Paths

Key-Value Observing

Key-Value Coding

Class Methods

array

Creates and returns an empty array.

+ (id)array

Return Value

An empty array.

Discussion

This method is used by mutable subclasses of NSArray.

Availability
See Also
Related Sample Code
Declared In
NSArray.h

arrayWithArray:

Creates and returns an array containing the objects in another given array.

+ (id)arrayWithArray:(NSArray *)anArray

Parameters
anArray

An array.

Return Value

An array containing the objects in anArray.

Availability
See Also
Related Sample Code
Declared In
NSArray.h

arrayWithContentsOfFile:

Creates and returns an array containing the contents of the file specified by a given path.

+ (id)arrayWithContentsOfFile:(NSString *)aPath

Parameters
aPath

The path to a file containing a string representation of an array produced by the writeToFile:atomically: method.

Return Value

An array containing the contents of the file specified by aPath. Returns nil if the file can’t be opened or if the contents of the file can’t be parsed into an array.

Discussion

The array representation in the file identified by aPath must contain only property list objects (NSString, NSData, NSArray, or NSDictionary objects).

Availability
See Also
Related Sample Code
Declared In
NSArray.h

arrayWithContentsOfURL:

Creates and returns an array containing the contents specified by a given URL.

+ (id)arrayWithContentsOfURL:(NSURL *)aURL

Parameters
aURL

The location of a file containing a string representation of an array produced by the writeToURL:atomically: method.

Return Value

An array containing the contents specified by aURL. Returns nil if the location can’t be opened or if the contents of the location can’t be parsed into an array.

Discussion

The array representation at the location identified by aURL must contain only property list objects (NSString, NSData, NSArray, or NSDictionary objects).

Availability
See Also
Declared In
NSArray.h

arrayWithObject:

Creates and returns an array containing a given object.

+ (id)arrayWithObject:(id)anObject

Parameters
anObject

An object.

Return Value

An array containing the single element anObject.

Availability
See Also
Related Sample Code
Declared In
NSArray.h

arrayWithObjects:

Creates and returns an array containing the objects in the argument list.

+ (id)arrayWithObjects:(id)firstObj, ...

Parameters
firstObj, ...

A comma-separated list of objects ending with nil.

Return Value

An array containing the objects in the argument list.

Discussion

This code example creates an array containing three different types of element:

NSArray *myArray;
NSDate *aDate = [NSDate distantFuture];
NSValue *aValue = [NSNumber numberWithInt:5];
NSString *aString = @"a string";
 
myArray = [NSArray arrayWithObjects:aDate, aValue, aString, nil];
Availability
See Also
Related Sample Code
Declared In
NSArray.h

arrayWithObjects:count:

Creates and returns an array that includes a given number of objects from a given C array.

+ (id)arrayWithObjects:(const id *)objects count:(NSUInteger)count

Parameters
objects

A C array of objects.

count

The number of values from the objects C array to include in the new array. This number will be the count of the new array—it must not be negative or greater than the number of elements in objects.

Return Value

A new array including the first count objects from objects.

Discussion

Elements are added to the new array in the same order they appear in objects, up to but not including index count.

Availability
See Also
Declared In
NSArray.h

Instance Methods

addObserver:forKeyPath:options:context:

Raises an exception.

- (void)addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(void *)context

Parameters
observer

The object to register for KVO notifications. The observer must implement the key-value observing method observeValueForKeyPath:ofObject:change:context:.

keyPath

The key path, relative to the receiver, of the property to observe. This value must not be nil.

options

A combination of the NSKeyValueObservingOptions values that specifies what is included in observation notifications. For possible values, see NSKeyValueObservingOptions.

context

Arbitrary data that is passed to observer in observeValueForKeyPath:ofObject:change:context:.

Special Considerations

NSArray objects are not observable, so this method raises an exception when invoked on an NSArray object. Instead of observing an array, observe the to-many relationship for which the array is the collection of related objects.

Availability
See Also
Declared In
NSKeyValueObserving.h

addObserver:toObjectsAtIndexes:forKeyPath:options:context:

Registers anObserver to receive key value observer notifications for the specified keypath relative to the objects at indexes.

- (void)addObserver:(NSObject *)anObserver toObjectsAtIndexes:(NSIndexSet *)indexes forKeyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(void *)context

Discussion

The options determine what is included in the notifications, and the context is passed in the notifications.

This is not merely a convenience method; invoking this method is potentially much faster than repeatedly invoking addObserver:forKeyPath:options:context:.

Availability
See Also
Related Sample Code
Declared In
NSKeyValueObserving.h

arrayByAddingObject:

Returns a new array that is a copy of the receiver with a given object added to the end.

- (NSArray *)arrayByAddingObject:(id)anObject

Parameters
anObject

An object.

Return Value

A new array that is a copy of the receiver with anObject added to the end.

Discussion

If anObject is nil, an NSInvalidArgumentException is raised.

Availability
See Also
Related Sample Code
Declared In
NSArray.h

arrayByAddingObjectsFromArray:

Returns a new array that is a copy of the receiver with the objects contained in another array added to the end.

- (NSArray *)arrayByAddingObjectsFromArray:(NSArray *)otherArray

Parameters
otherArray

An array.

Return Value

A new array that is a copy of the receiver with the objects contained in otherArray added to the end.

Availability
See Also
Related Sample Code
Declared In
NSArray.h

componentsJoinedByString:

Constructs and returns an NSString object that is the result of interposing a given separator between the elements of the receiver’s array.

- (NSString *)componentsJoinedByString:(NSString *)separator

Parameters
separator

The string to interpose between the elements of the receiver’s array.

Return Value

An NSString object that is the result of interposing separator between the elements of the receiver’s array. If the receiver has no elements, returns an NSString object representing an empty string.

Discussion

For example, this code excerpt writes "here be dragons" to the console: 

NSArray *pathArray = [NSArray arrayWithObjects:@"here",
    @"be", @"dragons", nil];
NSLog(@"%@",
    [pathArray componentsJoinedByString:@" "]);
Special Considerations

Each element in the receiver’s array must handle description.

Availability
See Also
Related Sample Code
Declared In
NSArray.h

containsObject:

Returns a Boolean value that indicates whether a given object is present in the receiver.

- (BOOL)containsObject:(id)anObject

Parameters
anObject

An object.

Return Value

YES if anObject is present in the receiver, otherwise NO.

Discussion

This method determines whether anObject is present in the receiver by sending an isEqual: message to each of the receiver’s objects (and passing anObject as the parameter to each isEqual: message).

Availability
See Also
Related Sample Code
Declared In
NSArray.h

count

Returns the number of objects currently in the receiver.

- (NSUInteger)count

Return Value

The number of objects currently in the receiver.

Availability
See Also
Related Sample Code
Declared In
NSArray.h

description

Returns a string that represents the contents of the receiver, formatted as a property list.

- (NSString *)description

Return Value

A string that represents the contents of the receiver, formatted as a property list.

Availability
See Also
Declared In
NSArray.h

descriptionWithLocale:

Returns a string that represents the contents of the receiver, formatted as a property list.

- (NSString *)descriptionWithLocale:(id)locale

Parameters
locale

An NSLocale object or an NSDictionary object that specifies options used for formatting each of the receiver’s elements (where recognized). Specify nil if you don’t want the elements formatted.

Return Value

A string that represents the contents of the receiver, formatted as a property list.

Discussion

For a description of how locale is applied to each element in the receiving array, see descriptionWithLocale:indent:.

Availability
See Also
Declared In
NSArray.h

descriptionWithLocale:indent:

Returns a string that represents the contents of the receiver, formatted as a property list.

- (NSString *)descriptionWithLocale:(id)locale indent:(NSUInteger)level

Parameters
locale

An NSLocale object or an NSDictionary object that specifies options used for formatting each of the receiver’s elements (where recognized). Specify nil if you don’t want the elements formatted.

level

A level of indent, to make the output more readable: set level to 0 to use four spaces to indent, or 1 to indent the output with a tab character.

Return Value

A string that represents the contents of the receiver, formatted as a property list.

Discussion

The returned NSString object contains the string representations of each of the receiver’s elements, in order, from first to last. To obtain the string representation of a given element, descriptionWithLocale:indent: proceeds as follows:

Availability
See Also
Declared In
NSArray.h

filteredArrayUsingPredicate:

Evaluates a given predicate against each object in the receiver and returns a new array containing the objects for which the predicate returns true.

- (NSArray *)filteredArrayUsingPredicate:(NSPredicate *)predicate

Parameters
predicate

The predicate against which to evaluate the receiver’s elements.

Return Value

A new array containing the objects in the receiver for which predicate returns true.

Discussion

For more details, see Predicate Programming Guide.

Availability
Declared In
NSPredicate.h

firstObjectCommonWithArray:

Returns the first object contained in the receiver that’s equal to an object in another given array.

- (id)firstObjectCommonWithArray:(NSArray *)otherArray

Parameters
otherArray

An array.

Return Value

Returns the first object contained in the receiver that’s equal to an object in otherArray. If no such object is found, returns nil.

Discussion

This method uses isEqual: to check for object equality.

Availability
See Also
Declared In
NSArray.h

getObjects:

Copies all the objects contained in the receiver to aBuffer.

- (void)getObjects:(id *)aBuffer

Availability
See Also
Declared In
NSArray.h

getObjects:range:

Copies the objects contained in the receiver that fall within the specified range to aBuffer.

- (void)getObjects:(id *)aBuffer range:(NSRange)aRange

Availability
See Also
Declared In
NSArray.h

indexOfObject:

Returns the lowest index whose corresponding array value is equal to a given object.

- (NSUInteger)indexOfObject:(id)anObject

Parameters
anObject

An object.

Return Value

The lowest index whose corresponding array value is equal to anObject. If none of the objects in the receiver is equal to anObject, returns NSNotFound.

Discussion

Objects are considered equal if isEqual: returns YES.

Availability
See Also
Related Sample Code
Declared In
NSArray.h

indexOfObject:inRange:

Returns the lowest index within a specified range whose corresponding array value is equal to a given object .

- (NSUInteger)indexOfObject:(id)anObject inRange:(NSRange)range

Parameters
anObject

An object.

range

The range of indexes in the receiver within which to search for anObject.

Return Value

The lowest index within range whose corresponding array value is equal to anObject. If none of the objects within range is equal to anObject, returns NSNotFound.

Discussion

Objects are considered equal if isEqual: returns YES.

Availability
See Also
Declared In
NSArray.h

indexOfObjectIdenticalTo:

Returns the lowest index whose corresponding array value is identical to a given object.

- (NSUInteger)indexOfObjectIdenticalTo:(id)anObject

Parameters
anObject

An object.

Return Value

The lowest index whose corresponding array value is identical to anObject. If none of the objects in the receiver is identical to anObject, returns NSNotFound.

Discussion

Objects are considered identical if their object addresses are the same.

Availability
See Also
Related Sample Code
Declared In
NSArray.h

indexOfObjectIdenticalTo:inRange:

Returns the lowest index within a specified range whose corresponding array value is equal to a given object .

- (NSUInteger)indexOfObjectIdenticalTo:(id)anObject inRange:(NSRange)range

Parameters
anObject

An object.

range

The range of indexes in the receiver within which to search for anObject.

Return Value

The lowest index within range whose corresponding array value is identical to anObject. If none of the objects within range is identical to anObject, returns NSNotFound.

Discussion

Objects are considered identical if their object addresses are the same.

Availability
See Also
Declared In
NSArray.h

initWithArray:

Initializes a newly allocated array by placing in it the objects contained in a given array.

- (id)initWithArray:(NSArray *)anArray

Parameters
anArray

An array.

Return Value

An array initialized to contain the objects in anArray. The returned object might be different than the original receiver.

Discussion

After an immutable array has been initialized in this way, it cannot be modified.

Availability
See Also
Declared In
NSArray.h

initWithArray:copyItems:

Initializes a newly allocated array using anArray as the source of data objects for the array.

- (id)initWithArray:(NSArray *)array copyItems:(BOOL)flag

Parameters
array

An array.

flag

If YES, each object in array receives a copyWithZone: message to create a copy of the object. In a managed memory environment, this is instead of the retain message the object would otherwise receive. The object copy is then added to the returned array.

If NO, then in a managed memory environment each object in array simply receives a retain message as it’s added to the returned array.

Return Value

An array initialized to contain the objects—or if flag is YES, copies of the objects—in array. The returned object might be different than the original receiver.

Discussion

After an immutable array has been initialized in this way, it cannot be modified.

Availability
See Also
Declared In
NSArray.h

initWithContentsOfFile:

Initializes a newly allocated array with the contents of the file specified by a given path.

- (id)initWithContentsOfFile:(NSString *)aPath

Parameters
aPath

The path to a file containing a string representation of an array produced by the writeToFile:atomically: method.

Return Value

An array initialized to contain the contents of the file specified by aPath or nil if the file can’t be opened or the contents of the file can’t be parsed into an array. The returned object might be different than the original receiver.

Discussion

The array representation in the file identified by aPath must contain only property list objects (NSString, NSData, NSArray, or NSDictionary objects).

Availability
See Also
Declared In
NSArray.h

initWithContentsOfURL:

Initializes a newly allocated array with the contents of the location specified by a given URL.

- (id)initWithContentsOfURL:(NSURL *)aURL

Parameters
aURL

The location of a file containing a string representation of an array produced by the writeToURL:atomically: method.

Return Value

An array initialized to contain the contents specified by aURL. Returns nil if the location can’t be opened or if the contents of the location can’t be parsed into an array. The returned object might be different than the original receiver.

Discussion

The array representation at the location identified by aURL must contain only property list objects (NSString, NSData, NSArray, or NSDictionary objects).

Availability
See Also
Declared In
NSArray.h

initWithObjects:

Initializes a newly allocated array by placing in it the objects in the argument list.

- (id)initWithObjects:(id)firstObj, ...

Parameters
firstObj, ...

A comma-separated list of objects ending with nil.

Return Value

An array initialized to include the objects in the argument list. The returned object might be different than the original receiver.

Discussion

After an immutable array has been initialized in this way, it can’t be modified.

Availability
See Also
Declared In
NSArray.h

initWithObjects:count:

Initializes a newly allocated array to include a given number of objects from a given C array.

- (id)initWithObjects:(const id *)objects count:(NSUInteger)count

Parameters
objects

A C array of objects.

count

The number of values from the objects C array to include in the new array. This number will be the count of the new array—it must not be negative or greater than the number of elements in objects.

Return Value

A newly allocated array including the first count objects from objects. The returned object might be different than the original receiver.

Discussion

Elements are added to the new array in the same order they appear in objects, up to but not including index count.

After an immutable array has been initialized in this way, it can’t be modified.

Availability
See Also
Declared In
NSArray.h

isEqualToArray:

Compares the receiving array to another array.

- (BOOL)isEqualToArray:(NSArray *)otherArray

Parameters
otherArray

An array.

Return Value

YES if the contents of otherArray are equal to the contents of the receiver, otherwise NO.

Discussion

Two arrays have equal contents if they each hold the same number of objects and objects at a given index in each array satisfy the isEqual: test.

Availability
Declared In
NSArray.h

lastObject

Returns the object in the array with the highest index value.

- (id)lastObject

Return Value

The object in the array with the highest index value. If the array is empty, returns nil.

Availability
See Also
Related Sample Code
Declared In
NSArray.h

makeObjectsPerformSelector:

Sends to each object in the receiver the message identified by a given selector, starting with the first object and continuing through the array to the last object.

- (void)makeObjectsPerformSelector:(SEL)aSelector

Parameters
aSelector

A selector that identifies the message to send to the objects in the receiver. The method must not take any arguments, and must not have the side effect of modifying the receiving array.

Discussion

This method raises an NSInvalidArgumentException if aSelector is NULL.

Availability
See Also
Related Sample Code
Declared In
NSArray.h

makeObjectsPerformSelector:withObject:

Sends the aSelector message to each object in the array, starting with the first object and continuing through the array to the last object.

- (void)makeObjectsPerformSelector:(SEL)aSelector withObject:(id)anObject

Parameters
aSelector

A selector that identifies the message to send to the objects in the receiver. The method must take a single argument of type id, and must not have the side effect of modifying the receiving array.

anObject

The object to send as the argument to each invocation of the aSelector method.

Discussion

This method raises an NSInvalidArgumentException if aSelector is NULL.

Availability
See Also
Related Sample Code
Declared In
NSArray.h

objectAtIndex:

Returns the object located at index.

- (id)objectAtIndex:(NSUInteger)index

Parameters
index

An index within the bounds of the receiver.

Return Value

The object located at index.

Discussion

If index is beyond the end of the array (that is, if index is greater than or equal to the value returned by count), an NSRangeException is raised.

Availability
See Also
Related Sample Code
Declared In
NSArray.h

objectEnumerator

Returns an enumerator object that lets you access each object in the receiver.

- (NSEnumerator *)objectEnumerator

Return Value

An enumerator object that lets you access each object in the receiver, in order, from the element at the lowest index upwards.

Discussion

Returns an enumerator object that lets you access each object in the receiver, in order, starting with the element at index 0, as in:

NSEnumerator *enumerator = [myArray objectEnumerator];
id anObject;
 
while (anObject = [enumerator nextObject]) {
    /* code to act on each element as it is returned */
}
Special Considerations

When you use this method with mutable subclasses of NSArray, you must not modify the array during enumeration.

On Mac OS X v10.5 and later, it is more efficient to use the fast enumeration protocol (see NSFastEnumeration).

Availability
See Also
Related Sample Code
Declared In
NSArray.h

objectsAtIndexes:

Returns an array containing the objects in the receiver at the indexes specified by a given index set.

- (NSArray *)objectsAtIndexes:(NSIndexSet *)indexes

Return Value

An array containing the objects in the receiver at the indexes specified by indexes.

Discussion

The returned objects are in the ascending order of their indexes in indexes, so that object in returned array with higher index in indexes will follow the object with smaller index in indexes.

Raises an NSRangeException exception if any location in indexes exceeds the bounds of the receiver.

Availability
See Also
Declared In
NSArray.h

pathsMatchingExtensions:

Returns an array containing all the pathname elements in the receiver that have filename extensions from a given array.

- (NSArray *)pathsMatchingExtensions:(NSArray *)filterTypes

Parameters
filterTypes

An array of NSString objects containing filename extensions. The extensions should not include the dot (“.”) character.

Return Value

An array containing all the pathname elements in the receiver that have filename extensions from the filterTypes array.

Availability
Declared In
NSPathUtilities.h

removeObserver:forKeyPath:

Raises an exception.

- (void)removeObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath

Parameters
observer

The object to remove as an observer.

keyPath

A key-path, relative to the receiver, for which observer is registered to receive KVO change notifications. This value must not be nil.

Special Considerations

NSArray objects are not observable, so this method raises an exception when invoked on an NSArray object. Instead of observing an array, observe the to-many relationship for which the array is the collection of related objects.

Availability
See Also
Declared In
NSKeyValueObserving.h

removeObserver:fromObjectsAtIndexes:forKeyPath:

Removes anObserver from all key value observer notifications associated with the specified keyPath relative to the receiver’s objects at indexes.

- (void)removeObserver:(NSObject *)anObserver fromObjectsAtIndexes:(NSIndexSet *)indexes forKeyPath:(NSString *)keyPath

Discussion

This is not merely a convenience method; invoking this method is potentially much faster than repeatedly invoking removeObserver:forKeyPath:.

Availability
See Also
Related Sample Code
Declared In
NSKeyValueObserving.h

reverseObjectEnumerator

Returns an enumerator object that lets you access each object in the receiver, in reverse order.

- (NSEnumerator *)reverseObjectEnumerator

Return Value

An enumerator object that lets you access each object in the receiver, in order, from the element at the highest index down to the element at index 0.

Special Considerations

When you use this method with mutable subclasses of NSArray, you must not modify the array during enumeration.

On Mac OS X v10.5 and later, it is more efficient to use the fast enumeration protocol (see NSFastEnumeration).

Availability
See Also
Related Sample Code
Declared In
NSArray.h

setValue:forKey:

Invokes setValue:forKey: on each of the receiver's items using the specified value and key.

- (void)setValue:(id)value forKey:(NSString *)key

Availability
See Also
Related Sample Code
Declared In
NSKeyValueCoding.h

sortedArrayHint

Analyzes the receiver and returns a “hint” that speeds the sorting of the array when the hint is supplied to sortedArrayUsingFunction:context:hint:.

- (NSData *)sortedArrayHint

Availability
See Also
Declared In
NSArray.h

sortedArrayUsingDescriptors:

Returns a copy of the receiver sorted as specified by a given array of sort descriptors.

- (NSArray *)sortedArrayUsingDescriptors:(NSArray *)sortDescriptors

Parameters
sortDescriptors

An array of NSSortDescriptor objects.

Return Value

A copy of the receiver sorted as specified by sortDescriptors.

Discussion

The first descriptor specifies the primary key path to be used in sorting the receiver’s contents. Any subsequent descriptors are used to further refine sorting of objects with duplicate values. See NSSortDescriptor for additional information.

Availability
See Also
Related Sample Code
Declared In
NSSortDescriptor.h

sortedArrayUsingFunction:context:

Returns a new array that lists the receiver’s elements in ascending order as defined by the comparison function comparator.

- (NSArray *)sortedArrayUsingFunction:(NSInteger (*)(id, id, void *))comparator context:(void *)context

Discussion

The new array contains references to the receiver’s elements, not copies of them.

The comparison function is used to compare two elements at a time and should return NSOrderedAscending if the first element is smaller than the second, NSOrderedDescending if the first element is larger than the second, and NSOrderedSame if the elements are equal. Each time the comparison function is called, it’s passed context as its third argument. This allows the comparison to be based on some outside parameter, such as whether character sorting is case-sensitive or case-insensitive.

Given anArray (an array of NSNumber objects) and a comparison function of this type:

NSInteger intSort(id num1, id num2, void *context)
{
    int v1 = [num1 intValue];
    int v2 = [num2 intValue];
    if (v1 < v2)
        return NSOrderedAscending;
    else if (v1 > v2)
        return NSOrderedDescending;
    else
        return NSOrderedSame;
}

A sorted version of anArray is created in this way:

NSArray *sortedArray; sortedArray = [anArray sortedArrayUsingFunction:intSort context:NULL];
Availability
See Also
Related Sample Code
Declared In
NSArray.h

sortedArrayUsingFunction:context:hint:

Returns a new array that lists the receiver’s elements in ascending order as defined by the comparison function comparator.

- (NSArray *)sortedArrayUsingFunction:(NSInteger (*)(id, id, void *))comparator context:(void *)context hint:(NSData *)hint

Discussion

The new array contains references to the receiver’s elements, not copies of them.

This method is similar to sortedArrayUsingFunction:context:, except that it uses the supplied hint to speed the sorting process. When you know the array is nearly sorted, this method is faster than sortedArrayUsingFunction:context:. If you sorted a large array (N entries) once, and you don’t change it much (P additions and deletions, where P is much smaller than N), then you can reuse the work you did in the original sort by conceptually doing a merge sort between the N “old” items and the P “new” items.

To obtain an appropriate hint, use sortedArrayHint. You should obtain this hint when the original array has been sorted, and keep hold of it until you need it, after the array has been modified. The hint is computed by sortedArrayHint in O(N) (where N is the number of items). This assumes that items in the array implement a -hash method. Given a suitable hint, and assuming that the hash function is a “good” hash function, -sortedArrayUsingFunction:context:hint: sorts the array in O(P*LOG(P)+N) where P is the number of adds or deletes. This is an improvement over the unhinted sort, O(N*LOG(N)), when P is small.

The hint is simply an array of size N containing the N hashes. To re-sort you need internally to create a map table mapping a hash to the index. Using this map table on the new array, you can get a first guess for the indices, and then sort that. For example, a sorted array {A, B, D, E, F} with corresponding hash values {25, 96, 78, 32, 17}, may be subject to small changes that result in contents {E, A, C, B, F}. The mapping table maps the hashes {25, 96, 78, 32, 17} to the indices {#0, #1, #2, #3, #4}. If the hashes for {E, A, C, B, F} are {32, 25, 99, 96, 17}, then by using the mapping table you can get a first order sort {#3, #0, ?, #1, #4}, so therefore create an initial semi-sorted array {A, B, E, F}, and then perform a cheap merge sort with {C} that yields {A, B, C, E, F}.

Availability
See Also
Declared In
NSArray.h

sortedArrayUsingSelector:

Returns an array that lists the receiver’s elements in ascending order, as determined by the comparison method specified by a given selector.

- (NSArray *)sortedArrayUsingSelector:(SEL)comparator

Parameters
comparator

A selector that identifies the method to use to compare two elements at a time. The method should return NSOrderedAscending if the receiver is smaller than the argument, NSOrderedDescending if the receiver is larger than the argument, and NSOrderedSame if they are equal.

Return Value

An array that lists the receiver’s elements in ascending order, as determined by the comparison method specified by the selector comparator.

Discussion

The new array contains references to the receiver’s elements, not copies of them.

The comparator message is sent to each object in the array and has as its single argument another object in the array.

For example, an array of NSString objects can be sorted by using the caseInsensitiveCompare: method declared in the NSString class. Assuming anArray exists, a sorted version of the array can be created in this way:

NSArray *sortedArray =
    [anArray sortedArrayUsingSelector:@selector(caseInsensitiveCompare:)];
Availability
See Also
Related Sample Code
Declared In
NSArray.h

subarrayWithRange:

Returns a new array containing the receiver’s elements that fall within the limits specified by a given range.

- (NSArray *)subarrayWithRange:(NSRange)range

Parameters
range

A range within the receiver’s range of elements.

Return Value

A new array containing the receiver’s elements that fall within the limits specified by range.

Discussion

If range isn’t within the receiver’s range of elements, an NSRangeException is raised.

For example, the following code example creates an array containing the elements found in the first half of wholeArray (assuming wholeArray exists).

NSArray *halfArray;
NSRange theRange;
 
theRange.location = 0;
theRange.length = [wholeArray count] / 2;
 
halfArray = [wholeArray subarrayWithRange:theRange];
Availability
Declared In
NSArray.h

valueForKey:

Returns an array containing the results of invoking valueForKey: using key on each of the receiver's objects.

- (id)valueForKey:(NSString *)key

Discussion

The returned array contains NSNull elements for each object that returns nil.

Availability
See Also
Related Sample Code
Declared In
NSKeyValueCoding.h

writeToFile:atomically:

Writes the contents of the receiver to a file at a given path.

- (BOOL)writeToFile:(NSString *)path atomically:(BOOL)flag

Parameters
path

The path at which to write the contents of the receiver.

If path contains a tilde (~) character, you must expand it with stringByExpandingTildeInPath before invoking this method.

flag

If YES, the array is written to an auxiliary file, and then the auxiliary file is renamed to path. If NO, the array is written directly to path. The YES option guarantees that path, if it exists at all, won’t be corrupted even if the system should crash during writing.

Return Value

YES if the file is written successfully, otherwise NO.

Discussion

If the receiver’s contents are all property list objects (NSString, NSData, NSArray, or NSDictionary objects), the file written by this method can be used to initialize a new array with the class method arrayWithContentsOfFile: or the instance method initWithContentsOfFile:. This method recursively validates that all the contained objects are property list objects before writing out the file, and returns NO if all the objects are not property list objects, since the resultant file would not be a valid property list.

Availability
See Also
Declared In
NSArray.h

writeToURL:atomically:

Writes the contents of the receiver to the location specified by a given URL.

- (BOOL)writeToURL:(NSURL *)aURL atomically:(BOOL)flag

Parameters
aURL

The location at which to write the receiver.

flag

If YES, the array is written to an auxiliary location, and then the auxiliary location is renamed to aURL. If NO, the array is written directly to aURL. The YES option guarantees that aURL, if it exists at all, won’t be corrupted even if the system should crash during writing.

Return Value

YES if the location is written successfully, otherwise NO.

Discussion

If the receiver’s contents are all property list objects (NSString, NSData, NSArray, or NSDictionary objects), the location written by this method can be used to initialize a new array with the class method arrayWithContentsOfURL: or the instance method initWithContentsOfURL:.

Availability
See Also
Declared In
NSArray.h

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© 2008 Apple Inc. All Rights Reserved. (Last updated: 2008-06-09)

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