iPhone 核心数据对多关系和取消对子对象的编辑

Question

我已经建立了以下关系(站点实体在这里并不重要):http://i.stack.imgur.com/6pzHn.gif

这里最主要的是我有一个 Find 实体，它可以有很多 FindPhotos。在我的应用程序中有一个编辑屏幕，您可以在其中编辑 Find 的属性以及添加/删除其 FindPhotos。这是重要的代码:

/* tapping the Save button */
- (IBAction)saveFind:(id)sender {
    [[self find] setFindName:findName];
    [[self find] setNotes:[self notes]];
    /* etc... */

    NSError *error;
    [[self context] save:&error];
    if (error) {
        NSLog(@"Error while saving find: %@", error);
    }

    [[self presentingViewController] dismissModalViewControllerAnimated:YES];
}

- (void) imagePickerController: (UIImagePickerController *) picker didFinishPickingMediaWithInfo: (NSDictionary *) info {   
    NSString *mediaType = [info objectForKey: UIImagePickerControllerMediaType];
    UIImage *originalImage, *editedImage, *imageToSave;

    // Handle a still image capture
    if (CFStringCompare ((__bridge CFStringRef) mediaType, kUTTypeImage, 0) == kCFCompareEqualTo) {

        editedImage = (UIImage *) [info objectForKey:UIImagePickerControllerEditedImage];
        originalImage = (UIImage *) [info objectForKey:UIImagePickerControllerOriginalImage];

        if (editedImage) {
            imageToSave = editedImage;
        } else {
            imageToSave = originalImage;
        }

        NSString *documentsDirectory = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"];
        NSString *pathName = [NSString stringWithFormat:@"/Photo%i.jpg", [NSString UUIDString]];
        NSString *jpgPath = [documentsDirectory stringByAppendingPathComponent:pathName];

        [UIImageJPEGRepresentation(imageToSave, 1.0) writeToFile:jpgPath atomically:YES];

        NSData * thumbnail = UIImageJPEGRepresentation([originalImage thumbnailImage:100 transparentBorder:0 cornerRadius:0 interpolationQuality:kCGInterpolationMedium], 1.0);

        FindPhoto *photo = [NSEntityDescription insertNewObjectForEntityForName:@"FindPhoto" inManagedObjectContext:[self context]];

        [photo setThumbnail:thumbnail];
        [photo setPath:jpgPath];
        [photo setFind:[self find]];

        [[self find] addPhotosObject:photo];
    }

    [picker dismissModalViewControllerAnimated: YES];
}

/* tapping the Cancel button */
- (IBAction)cancel:(id)sender {
    [[self presentingViewController] dismissModalViewControllerAnimated:YES];
}

/* deleting a photo */
- (void)photoWasDeleted:(MWPhoto *)mwphoto {
    for (FindPhoto *photo in [[self find] photos]) {
        if ([[photo path] isEqualToString:[mwphoto photoPath]]) {
            [[self find] removePhotosObject:photo];
            NSLog(@"Photo deleted");
            return;
        }
    }
}

通过点击“保存”按钮，将调用保存上下文的 saveFind 方法。问题是，即使我点击“取消”按钮，FindPhotos 仍将显示为已删除/已添加，即使我没有保存上下文也是如此。

我希望仅当我点击“保存”按钮时，FindPhoto 实体才会更改为“查找”。谁能给我推荐一种处理这种情况的方法？

Answer 1

有几种方法可以解决这个问题:

1. 为添加新对象创建附加上下文，取消时关闭上下文，保存时将上下文与主上下文合并

2. 使用撤消管理器，在取消时还原所有更改。使用撤消分组对所有更改进行分组