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Circular import issues in Objective C & Cocoa Touch

I have a view controller in Cocoa Touch that detects when the device rotates and switches between the views of the 2 view controllers it has: landscape and portrait.

I want the UIViewControllers in it to be able to access the FRRRotatingViewController, in a similar way as all UIViewControllers can access the UINavigationController they're in.

So I created a UIViewController subclass (FRRViewController) that will have a rotatingViewController property.

I also modified FRRRotatingViewController, so it takes FRRViewControllers instead of plain UIViewControllers.

Unfortunately, when I include FRRRotatingViewController.h in FRRViewController.h (and vice versa), I seem to get into a circular import issue. I don't know how to fix it. Any suggestions?

Here's the code:

//
//  FRRViewController.h

#import <UIKit/UIKit.h>
#import "FRRRotatingViewController.h"

@interface FRRViewController : UIViewController

@end

//
//  FRRRotatingViewController.h

#import <UIKit/UIKit.h>
#import "FRRViewController.h"

@class FRRRotatingViewController;


@protocol FRRRotatingViewControllerDelegate

-(void) FRRRotatingViewControllerWillSwitchToLandscapeView: (FRRRotatingViewController *) sender;
-(void) FRRRotatingViewControllerWillSwitchToPortraitView: (FRRRotatingViewController *) sender;

@end


@interface FRRRotatingViewController : FRRViewController {
    // This is where I get the error:Cannot find interface declaration for
    // 'FRRViewController', superclass of 'FRRRotatingViewController'; did you 
    // mean 'UIViewController'?
}

@property (strong) UIViewController *landscapeViewController;
@property (strong) UIViewController *portraitViewController;

@property (unsafe_unretained) id<FRRRotatingViewControllerDelegate> delegate;

-(FRRRotatingViewController *) initWithLandscapeViewController: (UIViewController *) landscape andPortraitViewController: (UIViewController *) portrait;
-(void) deviceDidRotate: (NSNotification *) aNotification;

@end
like image 408
cfischer Avatar asked Oct 14 '11 12:10

cfischer


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How do I fix circular import error?

If the error occurs due to a circular dependency, it can be resolved by moving the imported classes to a third file and importing them from this file. If the error occurs due to a misspelled name, the name of the class in the Python file should be verified and corrected.

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Generally, the Python Circular Import problem occurs when you accidentally name your working file the same as the module name and those modules depend on each other. This way the python opens the same file which causes a circular loop and eventually throws an error.


2 Answers

You can use forward declarations for classes and protocols in headers in most situations to avoid circular import issues, except in the case of inheritance. In FRRViewController.h, instead of importing FRRRotatingViewController.h, can you not make a forward declaration?

@class FRRRotatingViewController;
like image 198
jbat100 Avatar answered Sep 16 '22 23:09

jbat100


If I'm reading it right your inheritance structure is like so:

UIViewController-->FRRViewController-->FRRRotatingViewController

But you have made the declaration of FRRViewController dependent on importing the file from its subclass, FRRRotatingViewController. The compiler will therefore be importing and reading FRRRotatingViewController before it processes the rest of FRRViewController.h.

I'm assuming you've missed out some of FRRViewController.h since there is no reference to any rotating view controllers in there, but if you are declaring a property in .h of FRRRotatingViewController, then you need to use a forward declaration in FRRViewController.h:

@class FRRRotatingViewController

instead of

#import "FRRRotatingViewController.h"

The latter line, you can put in the first line of your FRRViewController.m file.

like image 39
jrturton Avatar answered Sep 18 '22 23:09

jrturton