Question

So long story short, I have some odd bugs in some code I’m messing with and it turns out that it comes from an object being identified as the wrong class.

Here is my code, with the NSLog statement I put before anything touches the object… I can’t figure out why it’s showing as the wrong class.

Photo.h

@interface Photo : NSObject
{
}

@property (nonatomic, retain) UIImage *image;
@property (nonatomic, retain) IBOutlet NSString *descr;

@end

Photo.m

@implementation Photo

@synthesize image;
@synthesize descr;

@end

CameraViewController.h

#include "Photo.h"

@interface CameraViewController : UIViewController <UIImagePickerControllerDelegate>
{
    IBOutlet UIImageView *imageView;
}

@property (nonatomic, retain) Photo *photo;

-(void)takePhoto;
-(void)resetImage;

@end

and finally…
CameraViewController.m

#import "Photo.h"
....

@implementation CameraViewController

@synthesize photo;

- (void)viewDidLoad
{
    [super viewDidLoad];
    NSLog(@"%@", NSStringFromClass([_photo class]));
    // Do any additional setup after loading the view.
}

This prints out:

UIImageView

I would expect it to print out

Photo

or at the very least

NSObject

Am I missing something???

Answer 1

Sending an object the class message retrieves that object’s dynamic type. The object must be assigned prior to querying it for its class. In other words, declaring a property as Photo* is not sufficient for its class to return Photo: you must also assign it an instance of Photo or one of its subclasses. In the later case, the result of sending class message will be different (i.e. the Class of the subclass will be returned).