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Global & Static Classes


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#1 Six222   Members   -  Reputation: 439

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Posted 29 February 2012 - 05:33 AM

Hey guys, I'm current working on my next game and I've made a couple so far but I've always felt that the code that I wrote for them is messy. I'm forever making every class global or static just so I can access them from somewhere else instead of having to pass refrences around. For example:

class EntityHandler
{
public:
	 void Tick();
	 void Draw();

	 static void AddNewEntity();
	 static void AddBullet();
private:
	 static vector<Bullet>BulletList;
	 static vector<Enemy>EnemyList;
};
I'm writing all of my classes like this just so I can add a new entity/bullet from anywhere in my code. Looking at I feel that it's correct, it works but I can't help thinking that it's just a bad way of programming.

I could just send a refrence to the EntityHandler to every class but the entities shouldn't have to know about that and I would also probably be sending in loads of other refrences to all the static classes I have just so I could perform 1 or 2 tasks. This isn't good but I honestly don't know how I could do it another way. I guess some sort of message/event system could work for this but I really don't know...

Anyway If anyone could point me in the right direction that would be awesome. Thanks

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#2 mrjones   Members   -  Reputation: 612

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Posted 29 February 2012 - 06:18 AM

You are right in that it is not the best solution. You are also right in that giving each class reference to EntityHandler would be a bad idea as it requires boilerplate code and creates minor memory overhead.

A slightly better approach (although not the best imho) would be something like this:
class EntityHandler {
  public:
    void Tick();
    void Draw();

    void AddNewEntity();
    void AddBullet();

  private:
    vector<bullet> BulletList;
    vector<enemy> EnemyList;
};


class Global {
  private:
    static EntityHandler entityHandler;

  public:
    static EntityHandler& getEntityHandler();
};

This way at least EntityHandler is no longer static and its instances can be used elsewhere when required.

However, accessing Global::getEntityHandler() is a bit unwieldy and the rest of the code will become dependent on global instances.
The solution I usually prefer is to instead have a non-static class and pass its reference on only to methods that actually need it:
class EntityHandler {
  public:
    void Tick();
    void Draw();

    void AddNewEntity();
    void AddBullet();

  private:
    vector<bullet> BulletList; 
    vector<enemy> EnemyList;
};

class Bullet {
  public:
    // Pass the reference of EntityHandler only to methods that actually require it
    // or some other class containing EntityHandler reference.
    // This way you won't have to worry about EntityHandler being destroyed before bullet as it would be generally 
    // passed from EntityHandler::Tick/Draw method.
    // It would also be completely painless to take a Bullet from one EntityHandler and put it to another as there
    // is no internal reference.
    void Tick(EntityHandler& e);
    void Draw(EntityHandler& e);
};

It might seem to be a bit of a hassle to pass it on to such functions, but there are generally quite few functions that should need to see something as grand as EntityHandler.

#3 Six222   Members   -  Reputation: 439

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Posted 29 February 2012 - 06:54 AM

I never thought of passing the EntityHandler down through like that /facepalm.. So I could for example do this?

class Bullet {
  public:
	void Tick(EntityHandler& e);
	void Draw(EntityHandler& e);
};

void EntityHandler::Tick()
{
	 vector<bullet>::Iterator it;
	 for(it = BulletList.begin(); it != BulletList.end(); it++)
	 {
	 	 (*it)->Tick(*this);
	 }
}



#4 mrjones   Members   -  Reputation: 612

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Posted 29 February 2012 - 09:36 AM

Precisely. I didn't write that part down before, but that is exactly what I meant.

#5 Six222   Members   -  Reputation: 439

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Posted 29 February 2012 - 09:40 AM

Precisely. I didn't write that part down before, but that is exactly what I meant.


I started re-writing some of the static classes to pass the EntityHandler down and other classes and it works well. Thanks for the help!

#6 Monkan   Members   -  Reputation: 640

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Posted 29 February 2012 - 04:09 PM

Also don't forget about namespaces, I never used to use them and now use them everywhere, they are really handy for wrapping things up and making it all a bit neater.
"To know the road ahead, ask those coming back."




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