Singleton mode: Two writing Modes

Singleton mode: Two writing Modes

Singleton mode is the most commonly used design mode in iOS development. There are two official iOS Singleton modes:

1. Common writing

# Import "LGManagerCenter. h" static LGManagerCenter * managerCenter; @ implementation LGManagerCenter + (LGManagerCenter *) sharedManager {if (! ManagerCenter) managerCenter = [[self allocWithZone: NULL] init]; return managerCenter;} @ end

2. Use GCD to create a singleton class

# Import "LGManagerCenter. h "@ implementation LGManagerCenter + (LGManagerCenter *) sharedManager {static dispatch_once_t predicate; static LGManagerCenter * managerCenter; dispatch_once (& predicate, ^ {managerCenter = [[LGManagerCenter alloc] init] ;}); return managerCenter ;}@ end

The dispatch_once function is executed only once.

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