iOS single-case design mode

The singleton pattern means that there is only one instance. The singleton pattern ensures that a class has only one instance, and instantiates itself and provides this instance to the system as a whole. This class is called a singleton class.
The singleton availability is very high and is available for global invocation, such as login user management.

1. + (Accountmanager *) Sharedmanager
2. {
3. static Accountmanager *sharedaccountmanagerinstance = nil;
4. static dispatch_once_t predicate;
5. Dispatch_once (&predicate, ^{
6. Sharedaccountmanagerinstance = [[Self alloc] init];
7. });
8. return sharedaccountmanagerinstance;
9. }

iOS single-case design mode