NSArray
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);
}