2

我有一个核心数据模型定义如下：

一个用户有很多事件。每个事件可以有许多图片。关系具有“级联”删除规则。

我试图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有某种释放或“最终确定”方法？

每个图片实体都有一个对存储在应用程序文档目录中的本地文件的引用。

当通过表视图的 commitEditingStyle 删除用户时，我可以通过逐步处理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获取结果控制器收到通知时，嵌套关系不包含任何对象。用户的事件集将没有任何实体可以单步执行和删除本地内容。这是为关系设置“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;
    }
}
4

1 回答 1

4

您可以prepareForDeletion在子类中实现该方法NSManagedObject。它在删除对象之前自动调用，因此您也可以从那里删除引用的文件。

于 2012-05-02T18:05:21.013 回答