Manually create a single case

The so-called Singleton is: an application (APP) has only one instantiation object, this object is a singleton, generally used for music player and Tool class

Here we teach you how to create a singleton manually, one is to use mutexes, and the other is to take advantage of Dispatch's one-time execution.

1//Create a singleton by mutual exclusion lock2+(instancetype) Sharednetworktools3 {4     //static modifier5     StaticNetworktools *tools =Nil;6     //To determine if an instantiated object exists7     //Mutual exclusion Lock8 @synchronized (self) {9         if(Tools = =Nil) {TenTools = [NetworktoolsNew]; One         } A     } -     returntools; - }

 the //One-time execution create a single case -+(instancetype) sharednetworktoolsonce - { -     //static modifier +     StaticNetworktools *tools =Nil; -      +     //thread-safe execution at once A     Staticdispatch_once_t Oncetoken; atDispatch_once (&oncetoken, ^{ -         if(!tools) { -Tools =[[Networktools alloc]init]; -         } -     }); -     returntools; in      -}

Manually create a single case