创建单例的方式

单例类的另外一种创建方式

+ (AccountManager *)sharedManager { 

    static AccountManager *sharedAccountManagerInstance = nil; 

 

    static dispatch_once_t predicate; dispatch_once(&predicate, ^{       

          sharedAccountManagerInstance = [[self alloc] init]; 

    });

 

    return sharedAccountManagerInstance; 

 

}