[graphiteman]

Where do I store a variable in Cocoa that is available to all of the code in the program?

[Dalgo]

Anywhere. It's just the same as in C. For example, you could declare an integer in main.m just above the main function like:
int myInt = 0;

It has an initial value of 0. In all of the other files that you want to have access to that integer, just put at the top of the file:

extern int myInt;

Then you can acces myInt everywhere. Just don't say:

extern myInt = 0;

Or else it'll throw an error at you. Only do the initialization at it's declaration.

[mr_sonicblue]

Another way to do it is to subclass NSApplication to provide some extra global data storage. I'm probably going to use this method to provide global access to an array of icons which are used in rather random areas of a program.

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[graphiteman]

Originally posted by mr_sonicblue:
Another way to do it is to subclass NSApplication to provide some extra global data storage. I'm probably going to use this method to provide global access to an array of icons which are used in rather random areas of a program.

How would I do this?

[Apocalypse]

You should actually try to avoid this where possible. It is bad programming style to get into globals because they don't allow you to "hide" implementation of any preprocessing that you might need it for some times. Also, you run the risk of forgetting what you are doing some time in later development (so only use a few if you have to use them at all). Best way to handle all of your data is to ensure that everything is tied to some object (worst comes to worst I use a "DataBank" object that everything can access) so that any operations being performed on the variables can be abstracted (happens without you having to think about it). This is also a VERY important in large programs where you are garruanteed to forget what you are doing sometime during development.

The upside is you get highly organized code and you only have to think about one process at a time (for example, you can assume that moveCrapAroundAndFutzWithThisNumber does exactly what it claims so you don't have to perform all those operations or even bother thinking about the scope of them) but the downside is that design modifications made late in development are a bitch to implement.

Sweet, Sweet University of Waterloo,
Jeff.

[mr_sonicblue]

Yea, globals are bad, in general. But they do make things tons easier in extreme cases.

Originally posted by graphiteman:
How would I do this?

Here's all I think you have to do:

1) Create a subclass of NSApplication in Interface Builder.
2) Create the files for you subclass.
3) Change the custom class of "File's Owner" to your subclass.
4) Just to check, save and exit Interface Builder. Go to the Applications Settings tab under Targets. In the "Cocoa-Specific" section, "Prinicpal class" should have changed to the name of you subclass.

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[tietokonetonttu]

Also adding new method to NSApplication or NSObject by categories. Of course you can't add new attributes with categories, but it is possible to use static variable in new method. If you add it into the NSObject class, value is available in every object inherited.

More info about categories from "Object-oriented Programming and the Objective-C Language" pages 91-94. Available from http://www.apple.com/developer .

--TKT