Implementing class: Cannot find superclass

Question

I have ForceGaugeViewController class and ForceGaugeController class. I'm trying to make the ForceGaugeController class be a subclass of ForceGaugeViewController, but I'm receiving errors.

Error:

Cannot find interface declaration for ForceGaugeViewController superclass of ForceGaugeController class.

ForceGaugeViewController.h

#import <UIKit/UIKit.h>
#import <math.h>
#import "HardwareController.h"
#import "ForceGaugeController.h"

@interface ForceGaugeViewController : UIViewController{
}
end

ForceGaugeViewController.m

#import "ForceGaugeViewController.h"

@implementation ForceGaugeViewController

ForceGaugeController.h

#import <Foundation/Foundation.h>
#import "ForceGaugeViewController.h"
#import "FMDatabase.h"
#import "FMResultSet.h"

@class ForceGaugeViewController;

// error here
@interface ForceGaugeController : ForceGaugeViewController{
}
@end

ForceGaugeController.m

#import "ForceGaugeController.h"

Answer 1

You can not only forward reference a class that you will inherit from or a protocol that you will implement. You just need to import the superclass in the header which you are already doing and then remove the @class declaration.

Edit: Also the superclass ForceGaugeViewController should not include the subclass ForceGaugeViewController in the header file.

ForceGaugeController.h

#import <Foundation/Foundation.h>
#import "ForceGaugeViewController.h"
#import "FMDatabase.h"
#import "FMResultSet.h"

@interface ForceGaugeController : ForceGaugeViewController{
 }
@end

Answer 2

Be sure to avoid circular imports: Make sure you do not import any of the header or implementation subclasses files into the superclass file where the superclass interface declaration is (.h file)