Graphics Programs Reference
In-Depth Information
Now we have ensured that multiple instances of
BNRItemStore
cannot be created. We
have also ensured that once the instance of
BNRItemStore
is created, it is never des-
troyed because a static variable (that never gets destroyed) always maintains ownership of
it.
In
BNRItemStore.h
, give
BNRItemStore
an instance variable to hold an array of
BNRItem
instances and declare two more methods:
#import <Foundation/Foundation.h>
@class BNRItem;
@interface BNRItemStore : NSObject
{
NSMutableArray *allItems;
}
+ (BNRItemStore *)sharedStore;
- (NSArray *)allItems;
- (BNRItem *)createItem;
@end
See the
@class
directive? That tells the compiler that there is a
BNRItem
class and that
it doesn't need to know this class's details in the current file. This allows us to use the
BNRItem
symbol in the declaration of
createItem
without importing
BNRItem.h
.
Using the
@class
directive can speed up compile times considerably because fewer files
have to be recompiled when one file changes. (Wonder why? Flip back and read
the sec-
In files that actually send messages to the
BNRItem
class or instances of it, you must im-
port the file it was declared in so that the compiler will have all of its details. At the top of
BNRItemStore.m
, import
BNRItem.h
.
#import "BNRItemStore.h"
#import "BNRItem.h"
In
BNRItemStore.m
, override
init
to create an instance of
NSMutableArray
and
assign it to the instance variable.
- (id)init
{
self = [super init];
if (self) {
allItems = [[NSMutableArray alloc] init];
}
return self;
}
Now implement the two methods in
BNRItemStore.m
.
