Objective-C Class Question?

Question

My head is about to explode with this logic, can anyone help?

Class A #imports Class B. Class A calls Method A in Class B.

This works great

Class B wants to send a response back to Class A from another method that is called from Method A. If you #import Class A from Class B, it is in effect an infinite loop and the whole thing crashes.

Is there a way to do this properly, like a parent type thing?

BTW, I'm developing for iPhone.

EDIT When i #import Class A from Class B i get this compiler error...

error: expected specifier-qualifier-list before 'StoreHoursCore'

Any ideas?

It's __not__ creating an infinite loop. The `#import` directive prevents a file from being included more than once. Please describe the compilation error you get from doing this. — zneak, Mar 13 '10 at 19:03

score 7 · Accepted Answer · edited May 23 '17 at 12:19

7

I believe that using the @class directive should solve your issue.

Using @class forward declares your class type in order that the compiler doesn't cough.

Take a look at this question on SO.

edited May 23 '17 at 12:19

Community

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answered Mar 13 '10 at 19:03

Jacob Relkin

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I would add that this is called "forward declararion" – Vladimir Mar 13 '10 at 19:05
you keep typing the same thing seconds before I do :/ – Brock Woolf Mar 13 '10 at 19:08
@Brock, who? Me, or @Vladimir? – Jacob Relkin Mar 13 '10 at 19:09
@Jacob Lol. Yeah what a coincidence! – Brock Woolf Mar 13 '10 at 19:52
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I would add that it's good practice to use #import only in the implementation file and to use the @class otherwise. The exception to this is when you have to import the header for a super class. It's not a hard and fast rule but it is the habit you should get into. – TechZen Mar 13 '10 at 20:10

Brock Woolf · Answer 2 · 2010-03-13T20:56:23.547

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Use @classto forward declare it as a class. This hints the compiler to know that it is a class, without having to cross include and compile the class multiple times (the reason you are getting your error). ie:

@class myClass;

The #importpreprocessor directive has protection against multiple includes, but the #include directive does not.

edited Mar 13 '10 at 20:56

answered Mar 13 '10 at 19:05

Brock Woolf

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Objective-C Class Question?

2 Answers2