ViewController type name not recognized in one class, but it is in another?

Question

I am getting a build semantic error in XCode when I attempt to build my project. I have 3 NSOperation classes setup to download information from the internet, process it, and send it to the parent view controller, an instance of ViewController. Here is the code for a working class:

#import <Foundation/Foundation.h>
#import "ViewController.h"

@interface ImageGetter : NSOperation

@property (nonatomic) int sid;
@property (nonatomic, retain) ViewController* pvc;

@end

Here is the code for the one that is not working:

#import <Foundation/Foundation.h>
#import "ViewController.h"

@interface CurrentGetter : NSOperation

@property (nonatomic) int sid;
@property (nonatomic, retain) ViewController* pvc;

@end

Error:

ERROR: Unknown type name 'ViewController'; did you mean 'UIViewController'?

Why am I getting this error? I imported ViewController.h in both files and only one is working.

ViewController.h:

#import <UIKit/UIKit.h>
#import <AVFoundation/AVFoundation.h>
#import <MediaPlayer/MediaPlayer.h>

#import "DataGetter.h"
#import "CurrentGetter.h"
#import "AppDelegate.h"

@interface ViewController : UIViewController <UITabBarDelegate>
{
    NSTimer* tmr;
}

@property (nonatomic) float max;
@property (nonatomic, retain) NSDictionary* plist;
@property (nonatomic, retain) NSArray* processingobj;

@property (nonatomic, retain) AVAudioPlayer* intro;
@property (nonatomic, retain) AVAudioPlayer* woop;

@property (nonatomic) float dataDone;
@property (nonatomic) BOOL introDone;
@property (nonatomic) BOOL currentDone;

@property (nonatomic) int newSid;
@property (nonatomic) int newPart;

@property (nonatomic, retain) NSMutableArray* views;

@property (nonatomic) int audioTab;
@property (nonatomic) int currentSid;
@property (nonatomic) BOOL isPlaying;

@property (nonatomic, retain) UIScrollView* partTab;
@property (nonatomic, retain) NSMutableArray* nowPlayingObj;
@property (nonatomic, retain) UINavigationBar* audioNav;

@property (nonatomic, retain) MPMoviePlayerController* player;
@property (nonatomic, retain) UILabel* elapsed;
@property (nonatomic, retain) UILabel* remaining;
@property (nonatomic, retain) UISlider* slider;
@property (nonatomic) BOOL sliderEditing;
@property (nonatomic, retain) UIButton* playBtn;

@property (nonatomic, retain) UITabBar* tabBar;

//Images

@property (nonatomic, retain) UIImage* announcement;
@property (nonatomic, retain) NSMutableArray* seriesBanners;
@property (nonatomic, retain) UIProgressView* prog;

- (void)plistDone;

@end

Is the .m file added to your target? – Mike D Mar 04 '13 at 16:39 — Mike D, Mar 04 '13 at 16:39
Show the contents of ViewController.h – Jim Rhodes Mar 04 '13 at 16:48 — Jim Rhodes, Mar 04 '13 at 16:48

ewrobinson · Accepted Answer · 2013-03-04T17:11:59.893

12

Try doing a forward declaration of the class in your CurrentGetter header file, like this:

@class ViewController;
@interface CurrentGetter : NSOperation

This tells the compiler that there exists a class called "ViewController." When there are circular dependencies, like when two classes have instances of each other, using forward declarations of the classes resolves the confusion that results.

edited Mar 04 '13 at 17:11

answered Mar 04 '13 at 16:44

ewrobinson

351
4
9

Well the build succeeded with that line. Can you explain why this worked? – Liftoff Mar 04 '13 at 17:10
Yeah, sorry. I'm a bit new to the site, so I forgot that it was considered good form to include explanations. Does my brief explanation make sense? – ewrobinson Mar 04 '13 at 17:12
So why did the ImageGetter class build properly when the CurrentGetter did not, even though they have the exact same code? – Liftoff Mar 04 '13 at 17:12
@David, if this worked then your ViewController.h must not be defining ViewController. – Jim Rhodes Mar 04 '13 at 17:13
1

How can I fix that? This must be some programming etiquette I'm not familiar with. – Liftoff Mar 04 '13 at 17:19
I just generally use forward declarations of my classes when in this situation. As far as I am aware, there is no programmatic way around it. – ewrobinson Mar 04 '13 at 17:27

ViewController type name not recognized in one class, but it is in another?

1 Answers1