On 30 Apr 2009, at 17:16, Dave DeLong wrote:
Hi Andre,
#import means that the compiler will only include the file once,
thus eliminating re-declaration errors. It does not, however,
eliminate the problems introduced by circular dependencies (which is
what you've got going here).
As a general rule, the only thing you should be #importing in a .h
file are header files from classes that are not from your
application or framework. (Except protocols, which I don't know of
a way to forward declare)
@protocol MyProtocol ;
Matt Gallagher discussed this recently on his excellent Cocoa With
Love blog: http://cocoawithlove.com/2009/04/8-confusing-objective-c-warnings-and.html
Cheers,
Dave
On Apr 30, 2009, at 12:55 AM, Andre Doucette wrote:
Hi everyone!
I have noticed a problem in a few projects and don't understand
why. I have found a work around, but it seems both unnecessary and
a pain due to warnings.
For one example, I have two classes, AppController and
NetworkController.
For the AppController class:
---------------------------------------------------------
#import <Foundation/Foundation.h>
#import "NetworkController.h"
@interface AppController : NSObject {
NetworkController *networkController;
}
@implementation AppController
- (void)awakeFromNib {
networkController = [[NetworkController alloc]
initWithAppController:self];
}
@end
And for the NetworkController class:
---------------------------------------------------------
#import <Foundation/Foundation.h>
#import "AppController.h"
@interface NetworkController : NSObject {
AppController *appController;
}
- (id)initWithAppController:(AppController *)inAppController;
@end
@implementation NetworkController
- (id)initWithAppController:(AppController *)inAppController {
self = [super init];
appController = inAppController;
return self;
}
@end
I want the two controllers to "know" about each other. The
AppController object is created in the NIB file, and in it's
awakeFromNib method, I create the NetworkController object, passing
in a reference to itself.
When trying to compile this, I get a series of errors. In my
AppController.m file, I get "error: syntax error before
AppController" and "warning: '@end' must appear in an
@implementation context". In my NetworkController.m, I get "error:
syntax error before 'NetworkController'".
It seems that it doesn't like the double #import, but I thought the
whole idea behind #import was that it ensured one-time includes. If
I take either #import "NetworkController.h" or #import
"AppController.h" and change them to forward declarations (that is,
@class NetworkController; or @class AppController;), this works,
but then I get a sprinkling of errors everywhere saying that
methods may not be implemented.
Any thoughts?
Thanks!
Andre
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