ios - 从 iOS CoreData 获取图像

Question

我有一个使用 NSData 属性 imageData 定义的核心数据实体。我在实体上为 image 设置了 setter 和 getter。

setter，setImage，只需调用[self setImageData:UIImagePNGRepresentation(img)];getter image 仅返回 [UIImage imageWithData:[self imageData]];

当我创建新实体并且获取的结果 Controller 加载新表行时，图像始终为 null。但是，如果我点击该行转到下一个 View Controller ，图像就会正常显示。

如何才能使其在保存发生并且 fetchResultsController 更新为新行后立即显示图像。

编辑:添加代码

图像片段的核心数据 header 和 getter/setter

.h
@property (nonatomic, retain) NSData * imageData;

@property (nonatomic, retain) UIImage *image;

.m
- (void)setImage:(UIImage *)image
{
    NSData *data = UIImagePNGRepresentation(image);
    [self setImageData:data];
}

- (UIImage *)image
{
    return [UIImage imageWithData:[self imageData]];
}

表格 View 代码

- (NSFetchedResultsController *)fetchedResultsController {

    if (_fetchedResultsController != nil) {
        return _fetchedResultsController;
    }

    [NSFetchedResultsController deleteCacheWithName:@"Artists"];

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"ArtistModel" inManagedObjectContext:[[BKDataManager sharedInstance] mainObjectContext]];
    [fetchRequest setEntity:entity];

    NSSortDescriptor *sort = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES];
    [fetchRequest setSortDescriptors:[NSArray arrayWithObject:sort]];

    [fetchRequest setFetchBatchSize:20];

    _fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:[[BKDataManager sharedInstance] mainObjectContext] sectionNameKeyPath:nil cacheName:@"Artists"];

    _fetchedResultsController.delegate = self;

    return _fetchedResultsController;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    ArtistTableViewCell *cell = (ArtistTableViewCell *)[tableView dequeueReusableCellWithIdentifier:@"ArtistsTableViewCell"];

    if(!cell) {
        cell = (ArtistTableViewCell *)[[[UINib nibWithNibName:@"ArtistTableViewCell" bundle:nil] instantiateWithOwner:nil options:nil] objectAtIndex:0];
    }

    ArtistModel *row = [[self fetchedResultsController] objectAtIndexPath:indexPath];

    [[cell artistNameLabel] setText:[row name]];
    [[cell artistImageView] setImage:[row image]]; // This is where it pulls from the artist model

    return cell;
}

保存到核心数据位

- (void)addArtistWithName:(NSString *)name confirmed:(BOOL)confirmed managedContext:(NSManagedObjectContext *)managedContext success:(BKClientIdResult)success failure:(BKClientError)failure
{
    NSDictionary *params = [NSDictionary dictionaryWithObjectsAndKeys:
                            name, @"name",
                            [NSNumber numberWithBool:confirmed], @"confirmed"
                            , nil];

    [[BKClient sharedInstance] postPath:@"/users/artists" parameters:params success:^(AFHTTPRequestOperation *operation, id responseObject) {
        if([[responseObject objectForKey:@"status"] boolValue]) {
            NSDictionary *result = [responseObject valueForKeyPath:@"payload.artist"];

            ArtistModel *artistModel = (ArtistModel *)[NSEntityDescription insertNewObjectForEntityForName:@"ArtistModel" inManagedObjectContext:managedContext];

            [artistModel setName:[result objectForKey:@"name"]];

                NSURLRequest *imageRequest = [NSURLRequest requestWithURL:[NSURL URLWithString:[result objectForKey:@"image"]]];

                AFImageRequestOperation *op = [AFImageRequestOperation imageRequestOperationWithRequest:imageRequest imageProcessingBlock:nil success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) {
                    [artistModel setImage:image];

                    [managedContext save:nil];

                    if(success) {
                        success(artistModel);
                    }
                } failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error) {
                    // TODO FIX
                }];

                [op start];
        } else {
            if(failure) {
                failure([NSError errorWithDomain:@"com.nf" code:0 userInfo:[responseObject objectForKey:@"error"]]);
            }
        }
    } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
        if(failure) {
            failure(error);
        }
    }];
}

Answer 1

根据您的问题，刷新数据的最简单方法是执行新的提取(通过NSFetchedResultsController)并在完成保存后重新加载 TableView 。

NSError *error = nil;
if (![[self fetchedResultsController] performFetch:&error]) {
    // error handling here...
}

[yourTableView reloadData];

或者，您可以考虑为您的 NSFetchedResultsController 设置委托(delegate)。欲了解更多信息，请查看此处NSFetchedResultsControllerDelegate doc和 core-data-tutorial-how-to-use-nsfetchedresultscontroller .

设置此委托(delegate)后，您可以监听托管上下文的更改并正确响应 TableView 修改(添加、删除、更新部分和行)。

附言如果您提供一些代码，我们将能够为您提供更详细的帮助。