iPhone iOS 如何在删除实体时删除从核心数据实体嵌套关系引用的本地文件

Question

我有一个核心数据模型，定义如下：

用户有许多事件。每个事件可以有很多图片。关系具有"级联"删除规则。

我正在尝试了解如何在实体消失时删除本地文件。核心数据实体在消失之前是否调用某种 dealloc 或"最终化"方法？

每个图片实体都有对存储在应用文档目录中的本地文件的引用。

当通过表视图的 commitEditStyle 删除用户时，我可以通过逐步浏览关系来删除图像并手动删除文件：

- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath
{
    {
        // Delete the managed object for the given index path
        NSManagedObjectContext *context = [[[RKObjectManager sharedManager] objectStore] managedObjectContext];
        AppUser* managedObject = [self.fetchedResultsController objectAtIndexPath:indexPath];
        //clean up local files before deleting the object
        [self deleteLocalContentForAppUser:managedObject];        
//now delete the object
        [context deleteObject:managedObject];
        // Save the context to remember deletion
        NSError* error = nil;
        if (![context save:&error]) {
            /*
             Replace this implementation with code to handle the error appropriately.
             abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. 
             */
            NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            abort();
        }
    }
}

但是，当通过其他方法删除实体，并且我的提取结果控制器收到有关它们的通知时，嵌套关系不包含任何对象。用户的事件集将没有任何实体要单步执行和删除本地内容。这是为关系设置的"级联"删除规则的结果吗？

- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject
       atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type
      newIndexPath:(NSIndexPath *)newIndexPath
{
//    UITableView *tableView = self.tableView;
//     
    AppUser* managedObject = anObject;
    switch(type) {
        case NSFetchedResultsChangeInsert:
            [self.tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationNone];
//             [self.tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            //             [self configureCell:[tableView cellForRowAtIndexPath:newIndexPath] atIndexPath:newIndexPath];
            break;
        case NSFetchedResultsChangeDelete:
            [self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationNone];

            //these methods cannot find any content to delete
            [managedObject deleteLocalImages];
            [managedObject deleteLocalContent];
            break;
        case NSFetchedResultsChangeUpdate:
            [self configureCell:[self.tableView cellForRowAtIndexPath:newIndexPath] atIndexPath:newIndexPath];
            [managedObject updateLocalImages];
            break;
        case NSFetchedResultsChangeMove:
            [self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
            [self.tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath]withRowAnimation:UITableViewRowAnimationFade];
            break;
    }
}

Answer 1

您可以在NSManagedObject子类中实现prepareForDeletion方法。在删除对象之前自动调用它，以便您也可以从那里删除引用的文件。