accessing a class's static method from an instance variable?

Question

Is there a way to access a class's static methods/variables from an instance variable? I've tried searching for an answer, but my searches only find why you can't access an instance method/variable within a static method. I get why static can't access instance, but I don't get instance can't access static.

Here's my situation: I'm a student making a top-down shooter game in XNA and I'm trying to use static Texture2Ds for each game object. I have a class GameObject that lays the basics for every other class, with two other main classes GameBot and Projectile that lays the basics for bots and projectiles respectively. My problem also has to do with this inheritance. I have all the collision code inside the GameBot and Projectile classes, and other classes like PlayerShip/EnemyShip or Cannonball/Missile inherit from them.

The problem I'm having is that I want to access a class method/variable from an instance variable of which I don't know the class. What I mean is, I pass my method a GameBot variable, but it could be either PlayerShip, EnemyShip, or any other child of GameBot, and each has different static texture data.

class GameBot : GameObject
{
    static protected Texture2D texture;
    static internal Color[] textureData;

    //etc...

    internal bool DidHitEnemy(GameBot enemyGameBot)
    {
        //Here, I want to access enemyGameBot.textureData
        //to do pixel-by-pixel collision
        //but A) enemyGameBot.textureData doesn't work
        //and B) enemyGameBot's class could be any child of GameBot
        //so I can't just use GameBot.textureData
    }

    static internal virtual Color[] GetTextureData()
    {
        return textureData;
        //I even thought about coding this function in each child
        //but I can't access it anyway
    }
}

This game is kind of an exercise in inheritance. I want to try to keep as much code as possible in classes higher up in the hierarchy, and only code the essential differences in each class. The reason I decided on static textures is so I can keep an array of Projectile in each GameBot, but be able to modify on-the-fly which Projectile (Cannonball, Missile, etc) is in some spot in that array. Without static projectiles, I'd have to assign the sprite every time I switch Projectiles. There reason I want one array of Projectile is so I can easily add another Projectile without having to add code everywhere.

Is there a way of accessing a static method/variable from an instance variable? If not, any suggestions of another way to keep the collision code as general as possible?

I have edited your title. Please see, "Should questions include “tags” in their titles?", where the consensus is "no, they should not". — John Saunders
– John Saunders, Commented Nov 21, 2012 at 21:58
GameBot.textureData works. What do you mean when you say it "doesn't work"? And are you aware of the typo in your class identifier definition (Gamebot vs. GameBot)? — Jeff
– Jeff, Commented Nov 21, 2012 at 22:02
Sorry about the GameBot/Gamebot confusion. I was free-typing that code. I'm clearly a useless coder without Intellisense. You're right. GameBot.textureData does work. I meant to say that enemyGameBot.textureData does not work. I think that GameBot.texture data would pull the textureData from the actual GameBot class (which would be null), whereas I want it to pull textureData from the child's class (PlayerShip, EnemyShip, etc). — Ray
– Ray, Commented Nov 21, 2012 at 23:09

Matthew Whited · Accepted Answer · 2012-11-21 22:20:50Z

7

An easy way to access this from the instance would be something like this...

public Color[] GetTextureData()
{        
    //note that `GameBot.` isn't required but I find it helpful to locate static 
    //calls versus `this.` for instance methods
    return GameBot.GetTextureDataInternal(); 
}

static internal Color[] GetTextureDataInternal()
{
    return textureData;
}

... you could then just call .GetTextureData() from your external variable instead of having to manage/maintain the static call separately.

edited Nov 21, 2012 at 22:20

answered Nov 21, 2012 at 22:04

Matthew Whited

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3 Comments

Svexo Over a year ago

a static virtual method is not possible as far as I know

Ray Over a year ago

This seems like what I was trying to do with the static virtual method. Looks like it'll work. I'll try it out. Thanks!

Matthew Whited Over a year ago

Seeing that you are using the XNA content manager for the textures you may just use the proper texture on the instance. The advantage of the singleton texture should be handled by the content manager. No reason for the extra layer of confusion.

Svexo · Accepted Answer · 2012-11-21 22:33:15Z

    class Gamebot : GameObject
{
    static Texture2D DefaultTexture;
    public virtual Texture2D Texture {get{return Gamebot.DefaultTexture;}}



    //etc...

    internal bool DidHitEnemy(Gamebot enemyGameBot)
    {

      //  enemyGameBot.Texture; // this will give you the texture of the enemyGameBot 
    }


}
class SmartBot : Gamebot
{
    static new Texture2D DefaultTexture;
    public override Texture2D Texture { get { return SmartBot.DefaultTexture; } }

}

In LoadContent you will assign the texture of each class

SmartBot.DefaultTexture = null;
GameBot.DefaultTexture =null;

You can do the same for the texturedata thing

EDIT: Btw if you have your texture you can extract the Color[] TextureData so you want need to keep it as an static

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