Difference between revisions of "NSArray"

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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 ===
Line 15: Line 17:
 
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);
}

See Also