Question

I am trying to use the Singleton design pattern via my abstract Charcter class so all sub classes can acces the object instance. Here is my singleton class:

 class GatewayAccess

{
private static GatewayAccess ph;

// Constructor is 'protected'
protected GatewayAccess()
{
}

public static GatewayAccess Instance()
{
  // Uses lazy initialization.
  // Note: this is not thread safe.
  if (ph == null)
  {
      ph = new GatewayAccess();
      Console.WriteLine("This is the instance");
  }

  return ph;
}
}

I can use this in my program.cs to create an instance no problem:

static void Main(string[] args)
    {
        GameEngine multiplayer = new GameEngine(5);

        Character Thor = new Warrior();
        Thor.Name = "Raymond";
        Thor.Display();
        Thor.PerformFight();
        Thor.PerformFight();
        multiplayer.Attach(Thor);

        GatewayAccess s1 = GatewayAccess.Instance();
        GatewayAccess s2 = GatewayAccess.Instance();

        if (s1 == s2)
        {
            Console.WriteLine("They are the same");
        }

        Console.WriteLine(Thor.getGamestate());

        Console.ReadLine();
    }

So what I want to do is allow the subclasses ie, warrior to access the instance of the Gateway, I just cannot figure out how to do this as the inheritance stuff is confusing me. Basically the gateway access is an access point to a database that can only have one connection at once. The singleton pattern was easy enough to understand, its just the mix of that and the inheritance. I was hoping once I achieved this, I could then do it in a thread safe manner.

I was also wondering how the Singleton instance could be dropped, as it is a connection to a database and can only be used by one character object at a time, then once the character object is done with it, it must free the singleton object up right?

I tried to use methods in my Character class to do all this but it isn’t working.

I appreciate any help with this.

Answer 1

I sense several design smells here.

• DB connection should not be Singleton – as you yourself mention, connections come and go, while the main point of Singleton is that it stays for the app’s lifetime
• Singleton and thread safety are not a good match
• Game characters should not have to work with the gateway (c’mon, what is a warrior to do with a database? 😉

You should better separate concerns and have DB / persistence handled by a different class which calls the game characters rather than vice versa.

It is difficult to give more specific advice with the little information you provided.