??????????????

????1??????????????????”??????????????“?????????
????2???????iOS?????????????У????????????????????????????????ж?????????ù????????????統(tǒng)??????????????????UIApplication??????????????????????????????”??ó??????“??????????????????????????????????Щ???????????????????????
????3?????????????????????????????????????????????????????￡?
1 //
2 //Singleton.h
3 //
4
5 @interface Singleton : NSObject
6
7 + (Singleton*)sharedManager;
8 //????
9 @property (nonatomic ??strong) NSString* singletonData;
10
11 @end
12
13 -------------------------------------------------------------------------
14
15 //
16 //Singleton.m
17 //
18
19 #import "Singleton.h"
20
21 @implementation Singleton
22  static Singleton *sharedManager = nil;
23 //???????????????
24 + (Singleton*)sharedManager
25 {
26     static dispatch_once_t once;
27     dispatch_once(&once?? ^{
28         sharedManager = [[self alloc] init];
29     });
30     return sharedManager;
31 }
32 //dispatch_once(dispatch_once_t *predicate?? dispatch_block_t block);
33 ??@end
????sharedManager?????????????dispatch_once??????GCD??????Grand Central Dispatch??????????C?????????????????????????????dispatch_once_t??????????????GCD??????壬??????GCD???????dispatch_once???????????????????????????????ù?????????????????????????????predicate??????ú?????????????????У???????????Σ??????????????????????????????????????@synchronized??????????????????????????????ε????????????predicate???????????????????predicate????????static????global?????Ρ?????д????????????????????????????????????Ч???????