Classes and Global Data

Question

OK, I've been battling how to do this with my test code and now it comes back to "bite" me in my new project.
In regular C, you just create your structures, fill them with data, and then your subroutines have full access to the global data.
With Objective-C you envelop certain data inside other objects. I got that. In fact, that's where I've gotten "stuck". Let me elaborate.
I have a the following classes:
Class (number of instances expected) description of class
Scenes (1) tables containing dictionaries of scenes and scene components
Pieces (1) tables containing images, type specs, etc. of game pieces
Blocks (1) tables with definitions, specs of movable game pieces
MainView (1) main application view, contains methods to draw the main gameboard
BlockView (n) view for the block and data needed to manipulate it by the main game logic
MainViewController (1) main controller for game screen
Ok, since MainView manages the game window it's init methods also call the init methods to instantiate the one instance of Scenes and Pieces which are needed to be setup in order for MainView to draw the currentScene using the UIImage figures for each of the pieces. So, it saves a pointer to the Scenes and Pieces instances. MainViewController can access those since it sets up MainView and has a pointer to it. MainViewController is currently where I had planned on firing up the BlockView subviews, one for each movable game blocks.
The problem comes with BlockView which has the logic to setup the additional data for each block type, but does not have a pointer to the instances of Scenes or Pieces which contain the current scene info and the UIImage dictionary to use for drawing the actual images on the screen. How can it get a pointer to the appropriate classes?
Since BlockView is invoked by MainViewController as it sets up the pieces, I could pass the pointer as part of the init method, but that seems like the WRONG place. Shouldn't I be able to put some block of pointers someplace where all objects can query to get the data needed (keeping it encapsulated within some master gameSettings object).
Actually that's part of where I'm going with this. I want to have a settings object which knows what scene is current, what block set (images) is in use (so I can have different images for each piece depending on which set is selected), and the saved state information needed to continue where I left off. (This part is mostly a serialization of the Blocks instances which contain both the initial and current locations on the screen, and the current background tableau which shows a more-or-less static background for each scene).
Instead of one object, right now I've separated the types of information by 3 classes, but everything needs access to two of those classes in order to fully function. I think I have that part under control. What I don't have is the BlockView instances and the GameLogic methods having access to the Scenes and Pieces data unless I pass a pointer to them during initialization.
Is that what I'm supposed to do?
Or is there a better way?
Lastly, my game logic is really a set of methods which act on ONE specific piece to move it, but then that movable piece (one of the instances of BlockView) is able to push other pieces as it moves. Additional methods will handle the pushing of the other instances of BlockView around until a solution is completed for the scene. That part, I think I've gotten OK, as the game logic will be Built into the Blocks or BlockView classes. (That's the part I will have to figure out).
I'm adding this to my query, so you know my intention, and whether I'm on the right track. So far my Blocks class only contains definitions used by BlockView, and no instance variables or methods yet. If all the logic can be put into the BlockView methods, I can probably throw Blocks away.
So, do I add a pointer to my init method...
- (id)initWithString:(NSString*)myType atPoint:(CGPoint)point
becomes
- (id)initWithString:(NSString*)myType atPoint:(CGPoint)point inScene:(Scene)scene ofSet:(Pieces)pieceSet
If that is what it takes, I can do it. It just seems there ought to be a better way.
Of course, I could abstract those last pointers to only provide the pieces needed for that one instantiation of a BlockView, as I have with 'myType' and 'point' by supplying only the 'pieceSet' to init, but then the game logic will need to have access to the 'scene' to know whether a given block is allowed to move to a given position. This is where I get confused as far as what information to pass to a class, since I know other methods invoked by touches will cause the blocks (in BlockView instances) to move around on the screen displayed by MainView.
Actually MainView will be detecting the touches and moving the instances of BlockView, so maybe the game logic SHOULD be in MainView instead. I just figured that to encapsulate it as methods that operate on the movable pieces, the methods should be in BlockView, and called by the touch detection routines in MainView.
Comments please. And don't say, you can do it either way... one way or the other, or yet a third way I don't fully comprehend (such as another viewController) should contain the logic. I think the logic is part of the model and not the view, but in this case, it affects the view based on the background squares and what happens to each block as it is moved or pushed "into" one of those squares.
Thanks in advance. I realize this may be a complicated question, but I think it is a fairly BASIC question, and my lack of Objective-C experience is showing.
To tie the question up a little better, I'm not expecting to have all objects have complete access to lots of global data. What I'm looking for is a place to put a pointer to each of my classes which are only ever instantiated once, and have that pointer be findable by any other class that can then query the appropriate class instance to retrieve the data. Right now, I have one and only one place holding these pointers, and am passing them to the objects/classes which need access to the data in those Scene and Pieces classes when they need them.
If that is the way I'm supposed to do it, then I'm on the right track, even if it means deciding which classes are allowed to hold and pass the appropriate object pointers to other objects.

Answer 1

etresoft wrote:
I think you are missing an important piece - the "model" - from the MVC architecture - Model, View, Controller.
Your "business logic" is composed of your Scenes, Pieces, and Blocks. That is your model. Your view shouldn't really know anything about that. Your controller understands both your model and your view and it puts the two together to draw things. You want to be able to swap our your GUI view for a text view, if you wanted to. Chess, for example, can be played in a GUI or from a text console. A more modern example is a multiplayer game. It has to function across a network so its model has to be projected to the local display as well as sent across the network.
Yes, I am still fighting with understanding the implementation of some concepts.
What I think I am wanting to do, is similar to what Apple has done with the file manager or notification centers, and be able to request information from my model as needed.
For example, my view doesn't care about the specifics of the scenes or pieces, yet my view wants to be able to display the name of the current scene or display the correct image for a piece. Right now, it keeps an instance pointer to my "singleton" Scene object, and using the scene index, gets the current name. To display images, it gets those from the Pieces singleton's image dictionary, and again keeps a pointer to do that.
What I would rather do is be able to get that pointer for the views that need it without having to copy it, or have back pointers to the superview which holds a copy of those pointers. My BlockView class layers the active pieces over the MainView which holds the playing board. To access things, my code looks like:MainView* mainView = (MainView*) self.superview;
NSString* key = [mainView.myScene.sceneKeys objectAtIndex:mainView.currentSceneIndex];
NSString* pieceName = [[mainView.myScene.scenes objectForkey:key] pieceAtLocation:loc];
UIImage* image = [mainView.myPieces.images objectForkey:pieceName];
Oh, and this isn't actual code. It is a contrived example. I have since made it more efficient.
What I think would be more appropriate would be something like this:
NSString* pieceName = [[Scenes CurrentScene] pieceAtLocation:loc];
UIImage* image = [[Pieces PieceImages] objectForkey:pieceName];
or even
UIImage* image = [[Pieces PieceImages] objectForKey:[[Scenes CurrentScene] pieceAtLocation:loc]];
When I attempt to create class methods to access data in my "singleton", I get lots of warnings about accessing instance data in a class method. So, instead I made everything an instance method, but that requires keeping a pointer to the instance available somewhere.
I have been able to recode some of the instance methods which manipulate derived strings from the instance data into class methods, but not the data read in from the plist data files.
What I'm missing is how to get the current "singleton" instance from the class, and then use that as the instance pointer, i.e. in the examples above, I guess that pieceAtLocation: would be an instance method, but CurrentScene and PieceImages would be class methods that return an instance pointer to the appropriate dictionaries. How to implement that correctly is where I'm still sketchy.
Isn't that how Apple has defined DefaultNotificationCenter or DefaultFileManager?
I've looked at some singleton code, and am not sure how it helps me get this done, so an example would definitely help.