Singleton Pattern

SingletonObject.h
#import <Foundation/Foundation.h>
@interface SingletonObject : NSObject {
@private
int count;
}

//統一透過此函式來使用 Singleton 物件的方法
+ (SingletonObject *)sharedSingletonObject;
//增加
- (void)addCount;
//呈現
- (void)showCount;
@end


1. #import "SingletonObject.h"
2.  
3. @implementation SingletonObject
4.  
5. //宣告一個靜態的Singleton物件
6. static SingletonObject *_singletonObject = nil;
7.  
8. - (id)init {
9. self = [super init];
10. if (self) {
11.  
12. //將 count 初始化為0
13. count = 0;
14. }
15.  
16. return self;
17. }
18.  
19. //執行時會判斷是否 _singletonObject 已經完成記憶體配置
20. + (SingletonObject *)sharedSingletonObject {
21.  
22. @synchronized([SingletonObject class]) {
23.  
24. //判斷_singletonObject是否完成記憶體配置
25. if (!_singletonObject)
26. [[self alloc] init];
27.  
28. return _singletonObject;
29. }
30.  
31. return nil;
32. }
33.  
34. + (id)alloc {
35. @synchronized([SingletonObject class]) {
36.  
37. //避免 [SingletonObject alloc] 方法被濫用
38. NSAssert(_singletonObject == nil, @"_singletonObject 已經做過記憶體配置");
39. _singletonObject = [super alloc];
40.  
41. return _singletonObject;
42. }
43.  
44. return nil;
45. }
46.  
47. - (void)addCount {
48. count += 1;
49. }
50.  
51. - (void)showCount {
52. NSLog(@"%d", count);
53. }
54.  
55. - (void)dealloc {
56. [super dealloc];
57. }
58.  
59. @end