了解NSNotifications和更新属性

Question

I have a photo taking app that has a PhotoViewController with the code below for notifications. There is also a button on this view controller that lauches the photo taking view controller which is opened modally and is presented in the PhotoViewController via delegation.

The PhotoViewVC.h contains:

@interface PhotoViewVC : UIViewController <UITextViewDelegate, PhotoTakingVCDelegate>

// Photo data
@property (nonatomic, strong) NSData *photoData;
@property (nonatomic, strong) NSString *photoText;
@property (nonatomic, strong) NSString *photoObject;
@property (nonatomic, strong) NSString *photoParentObject;
@property (nonatomic, strong) NSString *photoUsername;
@property (nonatomic, strong) NSNumber *photoBestCount;
@property (nonatomic, strong) NSNumber *photoReplyCount;
@property (nonatomic, strong) NSMutableAttributedString *photoLabel;
@property (nonatomic, assign) BOOL photoViewerAddedBests;

@end

The PhotoViewVC.m has:

- (void) viewDidLoad
{
    [self postNotification];
    [self listenToNotifications];
}

- (void) postNotification
{        
    NSDictionary *dataDict = [NSDictionary dictionaryWithObject:_photoObject forKey:@"photoObject"];

    [[NSNotificationCenter defaultCenter] postNotificationName:@"replyHappened" object:self userInfo:dataDict];
}

- (void) listenToNotifications
{
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(handleReplied:) name:@"replyHappened" object:nil];
}

- (void) handleReplied:(NSNotification *) note
{
    NSDictionary *data = [note userInfo];

    if (data != nil)
    {
        NSString *object = [data objectForKey:@"photoObject"];

        // Update counts
        int count = [_photoBestCount intValue];

        count = count + 1;

        _photoBestCount = [NSNumber numberWithInt:count];

        _bestsCount.text = [NSString stringWithFormat:@"%@", _photoBestCount];
    }
}

- (void) dealloc
{
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

// Now the PhotoTakingVC delegation functions:

- (void) photoTakingVCDismiss:(PostViewController *) sender
{
    [sender dismissViewControllerAnimated:YES completion:nil];
}

- (void) photoTakingVCPresent:(PostViewController *) sender
{
    [self dismissViewControllerAnimated:YES completion:nil];

    PhotoViewVC *best = [[PhotoViewVC alloc] init];

    best.photoData = _photoData;
    best.photoText = _photoText;
    best.photoObject = _photoObject;
    best.photoParentObject = _photoParentObject;
    best.photoUsername = _photoUsername;
    best.photoBestCount = _photoBestCount;
    best.photoReplyCount = _photoReplyCount;
    best.photoLabel = _photoLabel;
    best.photoViewerAddedBests = _photoViewerAddedBests;

    best.hidesBottomBarWhenPushed = YES;

    [self.navigationController pushViewController:best animated:NO];
}

- (void) photoView:(NSData *) photo andText:(NSString *) text andObject:(NSString *) object andParentObject:(NSString *) parentObject andUsername:(NSString *) username andBestCount:(NSNumber *) bestCount andReplyCount:(NSNumber *) replyCount andLabel:(NSMutableAttributedString *) label andAddedBests:(BOOL) addedBests
{
    _photoData = photo;
    _photoText = text;
    _photoObject = object;
    _photoParentObject = parentObject;
    _photoUsername = username;
    _photoBestCount = bestCount;
    _photoReplyCount = replyCount;
    _photoLabel = label;
    _photoViewerAddedBests = addedBests;
}

I am having trouble making my counts increase. So my app works like this:

1. PhotoTakingVC launches and creates all the best counts (initally 0).
2. PhotoViewVC is loaded correctly and best count is 0.
3. User is on PhotoViewVC and clicks reply button.
4. PhotoTakingVC pops up and takes photo.
5. PhotoViewVC creates a new instance of itself for new photo.
6. User hits back button on second instance of PhotoViewVC and goes back to first instance.
7. Bests count gets set to 1 which is correct.
8. Use on first instance of PhotoViewVC hits reply again.
9. Again PhotoTakingVC pops up and saves photo and its data.
10. PhotoViewVC via delegation creates another instance (third) of PhotoViewVC.
11. User clicks back on this third instance to go back to first instance.
12. Best count still is one and should be 2.

Why does _photoBestCount start at 0 every time and not continually increase?

Answer 1

In step 10 you state:

PhotoViewVC via delegation creates another instance (third) of PhotoViewVC.

Every time you create a new VC you're creating a new iVar _photoBestCount , initialized to zero. So if you want a persistent counter, just put this property in a Model class (call it PhotoCounter, or whatever). Create an instance of this class and pass it into PhotoViewVC. Now, every time you update this iVar you're using the same counter, not a new one