理解NSNotifications和更新属性

Question

我有一个拍照应用程序，它有一个PhotoViewController，下面的代码用于通知。在此视图控制器上还有一个按钮，该按钮调用通过委托在PhotoViewController中打开的照片拍摄视图控制器。

PhotoViewVC.h包含：

@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

PhotoViewVC.m有：

- (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;
}

我很难使我的计数增加。所以我的应用程序是这样工作的：

1. PhotoTakingVC启动并创建所有最佳计数(初始值为0)。
2. 正确加载PhotoViewVC，最佳计数为0。
3. 用户在PhotoViewVC上并单击“回复”按钮。
4. PhotoTakingVC弹出并拍照。
5. PhotoViewVC为新照片创建了一个自身的新实例。
6. 用户在PhotoViewVC的第二个实例上点击back按钮，然后返回到第一个实例。
7. 计数被设置为1，这是正确的。
8. 使用PhotoViewVC的第一个实例再次点击回复。
9. 再次，PhotoTakingVC弹出并保存照片及其数据。
10. PhotoViewVC通过委托创建PhotoViewVC的另一个实例(第三个)。
11. 用户单击第三个实例返回到第一个实例。
12. 最好的数仍然是1，应该是2。

为什么每次_photoBestCount从0开始，而不是持续增加？

Answer 1

在步骤10中，您声明：

PhotoViewVC通过委托创建PhotoViewVC的另一个实例(第三个)。

每次创建新的VC时，您都要创建一个新的iVar _photoBestCount，初始化为零。因此，如果您想要一个持久计数器，只需将该属性放入一个Model类(称为PhotoCounter或其他什么)。创建该类的一个实例并将其传递给PhotoViewVC。现在，每次更新这个iVar时，您使用的都是同一个计数器，而不是一个新的计数器