了解NSNotifications和更新属性

Question

我有一个照相应用程序，其中有一个PhotoViewController，下面的代码用于通知。 该视图控制器上还有一个按钮，用于启动拍照视图控制器，该按钮已打开并通过委托显示在PhotoViewController中。

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具有：

- (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;
}

我无法增加计数。 所以我的应用程序是这样的：

1. PhotoTakingVC启动并创建所有最佳计数（最初为0）。
2. PhotoViewVC已正确加载，最佳计数为0。
3. 用户在PhotoViewVC上，然后单击“答复”按钮。
4. PhotoTakingVC弹出并拍照。
5. PhotoViewVC为新照片创建其自身的新实例。
6. 用户在PhotoViewVC的第二个实例上单击后退按钮，然后返回到第一个实例。
7. 最佳计数被设置为1，这是正确的。
8. 在PhotoViewVC的第一个实例上使用再次击中回复。
9. 再次弹出PhotoTakingVC并保存照片及其数据。
10. PhotoViewVC通过委派创建了PhotoViewVC的另一个实例（第三个实例）。
11. 用户单击此第三实例将返回到第一实例。
12. 最佳计数仍为1，应为2。

为什么_photoBestCount每次都从0开始而不连续增加？

Answer 1

在步骤10中，您指出：

PhotoViewVC通过委派创建了PhotoViewVC的另一个实例（第三个实例）。

每次创建新的VC时，您都在创建一个新的iVar _photoBestCount ，并将其初始化为零。 因此，如果您想要一个持久计数器，只需将此属性放在Model类中（称为PhotoCounter或其他名称）即可。 创建此类的实例，并将其传递到PhotoViewVC。 现在，每次更新此iVar时，您使用的是同一计数器，而不是新计数器