OC中使用单例模式

 1 static Config * instance = nil;
 2 +(Config *) Instance
 3 {
 4     @synchronized(self)
 5     {
 6         if(nil == instance)
 7         {
 8             [self new];
 9         }
10     }
11     return instance;
12 }
13 
14 +(id)allocWithZone:(NSZone *)zone
15 {
16     @synchronized(self)
17     {
18         if(instance == nil)
19         {
20             instance = [super allocWithZone:zone];
21             return instance;
22         }
23     }
24     return nil;
25 }