Difference between revisions of "NSArray"
Line 7: | Line 7: | ||
The most common method to create an array is to just pass it a list: | The most common method to create an array is to just pass it a list: | ||
− | NSArray *array = [NSArray arrayWithObjects: @"John", @"Bob", [NSNull null], @"Jane"]; | + | NSArray *array = [NSArray arrayWithObjects: @"John", @"Bob", [NSNull null], @"Jane", nil]; |
− | When creating arrays remember that any kind of object can be included, but only objects can be included. | + | When creating arrays remember that any kind of object can be included, but only objects can be included. Note that <code>nil</code> values cannot be included in an array; you should use the <code>[[[NSNull]] null]</code> dummy object instead. |
+ | |||
+ | Note that when you provide a variable-length list of objects in Objective-C, you need to "terminate" the list with <code>nil</code>. Otherwise, the function has no way of knowing how many arguments there are. | ||
=== Copy an Array === | === Copy an Array === | ||
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A copy of an array can be done simply by doing the following: | A copy of an array can be done simply by doing the following: | ||
− | NSArray *array1 = [NSArray arrayWithObjects: @"John", @"Bob", [NSNull null], @"Jane"]; | + | NSArray *array1 = [NSArray arrayWithObjects: @"John", @"Bob", [NSNull null], @"Jane", nil]; |
NSArray *array2 = [NSArray arrayWithArray: array1]; | NSArray *array2 = [NSArray arrayWithArray: array1]; | ||
Revision as of 04:21, 12 May 2009
NSArray is an immutable, integer indexed, array of objects.
Creating Arrays
From a List
The most common method to create an array is to just pass it a list:
NSArray *array = [NSArray arrayWithObjects: @"John", @"Bob", [NSNull null], @"Jane", nil];
When creating arrays remember that any kind of object can be included, but only objects can be included. Note that nil
values cannot be included in an array; you should use the [[[NSNull]] null]
dummy object instead.
Note that when you provide a variable-length list of objects in Objective-C, you need to "terminate" the list with nil
. Otherwise, the function has no way of knowing how many arguments there are.
Copy an Array
A copy of an array can be done simply by doing the following:
NSArray *array1 = [NSArray arrayWithObjects: @"John", @"Bob", [NSNull null], @"Jane", nil]; NSArray *array2 = [NSArray arrayWithArray: array1];
From an Array
An array object can be made with a regular array of objects, as shown in the following example:
id array1[4] = {@"John", @"Bob", [NSNull null], @"Jane"}; NSArray *array2 = [NSArray arrayWithObjects: array1 count: 4];
Count being the number of objects from the array to be used.
Code chunks
Create index dictionary
Following NSArray category method creates a dictionary which works as an index by an attribute of contained objects. It uses Key Value Coding.
- (NSDictionary *)indexDictionaryForKey:(NSString *)key { NSMutableDictionary *dict = [[NSMutableDictionary alloc] init]; NSDictionary *retval; NSEnumerator *enumerator; id object; enumerator = [self objectEnumerator]; while( (object = [enumerator nextObject]) ) { [dict setObject:object forKey:[object valueForKey:key]]; } retval = [[NSDictionary alloc] initWithDictionary:dict]; RELEASE(dict); return AUTORELEASE(retval); }