Accessing Method from other Classes Objective-C

Question

Looked for an answer for this question, but I haven't found a suitable one yet. I'm hoping you guys (and gals) can help me out! (This is for an iPhone app)

Alright, I have a Mutliview application. Each view has it's own class, and everything is happy. However, the different classes sometimes call the same method. Up until now, I have simply wrote that Method twice, in both of the class files.

This is what I want to do though:

I want to make a new class, in It's own file, that has all the "Common" Methods. Then, whenever another class needs to call the Method, I simply call it from the other file. This way, when I want to change the Method, I only need to change it in one place, and not all the places...

I'm not sure how I'd do this, which is why I'm asking for help. I'm a little rusty and new for Objective-C, so pretty examples will help me a lot. Allow me to give you one.

File: ViewController1.m

@implementation ViewController1

//Do Some awesome stuff....

CALL "CommonMethod" HERE

@end

File: ViewController2.m

@implementation ViewController2

//Do Some awesome stuff....

CALL "CommonMethod" HERE

@end

File: CommonClass

@implementation commonClass

- (void)CommonMethod:(id)sender
{

//So some awesome generic stuff...



    }
@end

I feel like I need to #import the other file, make an Object from the class and call the Method from the Object... How do I do that?

Thanks again!

Answer 1

It sounds to me like the common code doesn't need to be in a class at all. Is there a reason you can't just use a C-style function for what you want to do?

You could put the common code in a class and then make your other two classes subclasses of that one; this method also avoids the code duplication.

Another option might be to write a class method instead of instance methods for this common code. I think most people feel that singletons are best avoided as a design choice.

It would be easier to give a good answer if we knew more about what you were really trying to accomplish.

Answer 2

What you want to do is to make the two controllers share a common superclass:

UIViewController : MyAwesomeViewController : ViewController1
                                           : ViewController2

commonMethod: would then reside in MyAwesomeViewController. Also, don't start method names with capital letters. :)

To elaborate:

+@interface MyAwesomeController : UIViewController {

-@interface ViewController1 : UIViewController { // and ditto for ViewController2
+@interface ViewController1 : MyAwesomeController {

Answer 3

Bear in mind that Objective-C is just a superset of C, and that whilst #include directives are mostly used for header files, there's nothing stopping you using a #include to embed the contents of one implementation inside another implementation. If the code is truly identical, you can easily just stick it in its own file, and #include it in the .m file.

Having said that, perhaps it would be better to use this technique in conjunction with categories, especially if the same implementation has similar behaviours.

Answer 4

Pass in a reference to your commonClass when you alloc and init your views...

CommonClass *cc = [[CommonClass alloc] init];

ViewController1 *vc1 = [[ViewController1 alloc] ... initWith:cc];
ViewController2 *vc2 = [[ViewController2 alloc] ... initWith:cc];

but making a classic c include might suffice.

Answer 5

Option 1:

@implementation commonClass
+ (void)CommonMethod:(id)sender  /* note the + sign */
{
//So some awesome generic stuff...
    }
@end

@implementation ViewController2

- (void)do_something... {
    [commonClass CommonMethod];
}


@end

Option 2:

@implementation commonClass
- (void)CommonMethod:(id)sender
{
//So some awesome generic stuff...
    }
@end

@implementation ViewController2

- (void)do_something... {
    commonClass *c=[[commonClass alloc] init];
    [c CommonMethod];
    [c release];
}

@end

Option 3: use inheritance (see Mr. Totland's description in this thread)

@implementation commonClass
- (void)CommonMethod:(id)sender
{
//So some awesome generic stuff...
    }
@end

/* in your .h file */
@interface ViewController2: commonClass

@end

naturally you always need to #import commonClass.h in your view controllers..

Answer 6

There are some answers here telling you to create a common "parent" class. However I think that you can do a lot better. Create a category for UIViewController instead. You don't know all of the internals of what is going on with UIViewController so I don't think it is worth creating your own View Controller hierarchy off of. In fact it could be dangerous. I ran into a number of problems when I tried to create a "base" UITableViewController and then create classes that inherit from that. I avoided these problems by using categories instead.

Your #1 priority shouldn't be inheriting things for no good reason, it should be getting an app into the app store that people will want to download.

Answer 7

I implemented Option 2, but when I release the c variable with [c release]; the application crashes. If I do not release it, the application works fine, but leaks memory. What can I do?