了解NSNotifications并更新属性

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。该视图控制器上还有一个按钮，用于启动拍照视图控制器，该控制器以模式打开，并通过委派显示在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;
}

我很难增加计数。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（最初为0）
2. PhotoViewVC加载正确，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为新照片创建一个自己的新实例
6. 用户在PhotoViewVC的第二个实例上点击后退按钮，然后返回到第一个实例
7. 最佳计数设置为1，这是正确的
8. 在PhotoViewVC的第一个实例上使用再次点击回复
9. 再次弹出PhotoTakingVC并保存照片及其数据
10. PhotoViewVC通过委派创建PhotoViewVC的另一个实例（第三个）
11. 用户单击第三个实例返回第一个实例
12. 最佳计数仍然是1，应该是2

为什么_photoBestCount每次都从0开始，而不是不断增加？

Answer 1

在步骤10中，您声明：

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

每次创建一个新的VC时，都会创建一个初始化为零的新iVar _photoBestCount。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（称之为PhotoCounter，或其他什么）。创建此类的实例并将其传递到PhotoViewVC中。现在，每次更新这个iVar时，都使用相同的计数器，而不是新的