Question

First i’ll just state that I’m using singletons that won’t actually be around throughout the entire app life time. It’s more a way of encapsulating what is going on from the user.

I have several GameStates, eg InGame or MainMenu, and these have some quite similar function calls so I thought to use inheritence to stop copy / pasting. The following code is what I have, but it does not work as I intend. Here it is:

BaseState.cs

abstract class BaseState
{
    protected static BaseState mHandle = null;

    protected static BaseState Handle
    {
        get
        {
            return mHandle;
        }
        set
        {
            mHandle = value;
        }
    }

    public static GameState UpdateState(GameTime gameTime)
    {
        GameState g = GameState.MainMenu;

        try
        {
            Handle.Update(gameTime);
        }
        catch (Exception e)
        {

        }

        return g;
    }

    public static void DrawState(GameTime gameTime, SpriteBatch spriteBatch)
    {
        Handle.Draw(gameTime, spriteBatch);
    }

    public static void Release()
    {
        mHandle = null;
    }

    protected abstract GameState Update(GameTime gameTime);
    protected abstract void Draw(GameTime gameTime, SpriteBatch spriteBatch);
}

InGame.cs

class InGame : BaseState
{
    private InGame()
    {

    }

    protected static new BaseState Handle
    {
        get
        {
            if (mHandle == null)
            {
                mHandle = new InGame();
            }

            return mHandle;
        }
        set
        {
            mHandle = value;
        }
    }

    protected override GameState Update(GameTime gameTime)
    {
        return GameState.Quit;
    }

    protected override void Draw(GameTime gameTime, SpriteBatch spriteBatch)
    {

    }
}

You can probably tell that I want to be able to use the get and set of InGame in the BaseState so I can simply call Handle.Update() and no matter if I called it from InGame or Menu or whatever it would know which code to use.

Obviously I need to brush up on my OO skills. But if anyone could suggest a way to get this to do what I would like it to, or to suggest a different way of going about it I would be grateful. Thanks.

Answer 1

What you are trying to achieve does not require a singleton, see below:

public abstract class BaseState
{
    public GameState UpdateState(GameTime gameTime)
    {
        GameState g = GameState.MainMenu;

        try
        {
            g = Update(gameTime); // Update returns a new state
        }
        catch (Exception e)
        {

        }

        return g;
    }

    protected abstract GameState Update(GameTime gameTime);
    protected abstract void Draw(GameTime gameTime, SpriteBatch spriteBatch);
}

public class InGame : BaseState
{
    public InGame()
    {

    }

    protected override GameState Update(GameTime gameTime)
    {
        return GameState.Quit;
    }

    protected override void Draw(GameTime gameTime, SpriteBatch spriteBatch)
    {
        // Draw game
    }
}

public class InMenu : BaseState
{
    public InMenu()
    {

    }

    protected override GameState Update(GameTime gameTime)
    {
        return GameState.Pause;
    }

    protected override void Draw(GameTime gameTime, SpriteBatch spriteBatch)
    {
        // Draw menu
    }
}

public void Foo()
{
    List<BaseState> states = new List<BaseState>();
    states.Add(new InGame());
    states.Add(new InMenu());

    // Calls InGame.Update(...)
    states[0].UpdateState(...);

    // Calls InMenu.Update(...)
    states[1].UpdateState(...);
}