Singleton Class (C++/ Objectve-C)

1.SingleThreaded.h

class Singleton {

public:
   static Singleton* getInstance();   //This will get us the singleton class instance
   ~Singleton();

private:
   static Singleton* pInstance; //Flag if the instance already exists or not

   //Constructot must be private
   Singleton()
   {
        //private constructor
   }

   Singleton(const Singleton);                  // Prevent copy-construction
   Singleton operator=(const Singleton);        //Prevent assignment
};
 

2.SingleThreaded.cpp

//Initialize the static pInstance variable
Singleton* Singleton::pInstance = 0;

//Get our instane
Singleton* Singleton::getInstance() {
   if (pInstance == 0) {
      pInstance = new Singleton;
   }
   return pInstance;
}

----------------------------------------------
//USE IT
Singleton* object = Singleton::getInstance();

3.ObjectiveC.h

#import <foundation/Foundation.h>

@interface MyManager : NSObject


//Static function
+ (id)getInstance;

//Optionally make a custom constructor
-(void)initRequiredVariables;

//convenience declaration to get the singleton instance in the .h file
#define Manager [MyManager getInstance]

@end

4.ObjectiveC.mm

#import "MyManager.h"

@implementation MyManager


#pragma mark - Singleton Methods

+ (id)getInstance {
    //Static variable initialized once
    static MyManager *pInstance = nil;

    //The way we ensure that it’s only created once is by using the dispatch_once method from Grand Central Dispatch (GCD)
    static dispatch_once_t onceToken;

    dispatch_once(&onceToken, ^{
        pInstance = [[self alloc] init];
    });

    return pInstance;
}

//Contructor
- (id)init {
  if (self = [super init]) {
      
  }
  return self;
}

//Custom constructor
-(void)initRequiredVariables {

}

- (void)dealloc {
  // Should never be called, but just here for clarity really.
}

@end

----------------------------------------------
//USE IT
MyManager *object = [MyManager getInstance];


//USE IT with the convenience declaration from the h file
Manager.someMemberMethodOrProperty

5.ClassicSingleton.java

public class ClassicSingleton {
  
   private static ClassicSingleton instance = null;
   
   protected ClassicSingleton() {
      // Exists only to defeat instantiation.
   }
   
   
   public static ClassicSingleton getInstance() {
      if(instance == null) {
         instance = new ClassicSingleton();
      }
      return instance;
   }
}