How to add extra .h and .m files to Obj-C project

Question

When creating a project in straight 'C' I can manage to split lengthy code into multiple h/c groups without issues. However, while I've been dabbling in Obj-C for a few years now I still can't grasp the following fundamental issue (perhaps because of my old C-style thinking and great-grandfatherly age?), which has led to the habit of writing huge, monolithic files which are hard to read/edit etc. I've tried everything I can think of and spent weeks searching the net for answers, but all to no avail.

Just suppose I create an NSObject instance called 'AppController, which contains the required h/m files. The interface file is basically laid out like so:

#import <Cocoa/Cocoa.h>

@interface AppController : NSObject
{
    IBOutlets etc here...
}

method declarations here…

@end

while the implementation file looks like so:

#import "AppController.h"

@implementation AppController

actual methods here …

@end

NOW suppose I want to add two extra h/m files called 'temperature'. In other words, I'm after four files in my project, namely:

AppController.h
AppController.m
temperature.h
temperature.m

I get that I'd have to #import the temperature interface file into my main AppController implementation file of course, but would I also need to create them as NSObject classes? These templates come with their own pre-written references to super etc. which cause all kinds of compiler issues and even more confusion.

Perhaps following my super-basic code snippet examples above, how would the temperature.h, temperature.m (and AppController.m) files be laid out so they can talk to each other? Where am I going wrong?

Answer 1

Since temperature files contain free functions, there's nothing more you need to do. You can simply call C functions from within Objective-C classes. If you want to make a class out of them, you can do that, too. It doesn't have to inherit from NSObject, but it can be useful to do that because it allows you to call various NSObject methods on it, such as -respondsToSelector:, -isKindOfClass: or -performSelector:.