如何实现CoreData记录的重新排序？ [英] How to implement re-ordering of CoreData records?

问题描述

我为我的iPhone应用程序使用CoreData，但CoreData不提供允许您重新排序记录的自动方式。我想到使用另一列来存储顺序信息，但使用连续数字进行排序索引有一个问题。如果我处理大量的数据，重新排序一个记录可能涉及更新大量的记录的排序信息（这有点像改变数组元素的顺序）

I am using CoreData for my iPhone app, but CoreData doesn't provide an automatic way of allowing you to reorder the records. I thought of using another column to store the order info, but using contiguous numbers for ordering index has a problem. if I am dealing with lots of data, reordering a record potentially involves updating a lot of records on the ordering info (it's sorta like changing the order of an array element)

推荐答案

FetchedResultsController及其委托不能用于用户驱动模型变化。请参阅 Apple参考文档。
查找用户驱动的更新部分。

FetchedResultsController and its delegate are not meant to be used for user-driven model changes. See the Apple reference doc. Look for User-Driven Updates part. So if you look for some magical, one-line way, there's not such, sadly.

你需要做的是在这个方法中进行更新：

What you need to do is make updates in this method:

- (void)tableView:(UITableView *)tableView moveRowAtIndexPath:(NSIndexPath *)fromIndexPath toIndexPath:(NSIndexPath *)toIndexPath {
 userDrivenDataModelChange = YES;

 ...[UPDATE THE MODEL then SAVE CONTEXT]...

 userDrivenDataModelChange = NO;
}

，并且还阻止通知执行任何操作，用户：

and also prevent the notifications to do anything, as changes are already done by the user:

- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
 if (userDrivenDataModelChange) return;
 ...
}
- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath {
 if (userDrivenDataModelChange) return;
 ...
}
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
 if (userDrivenDataModelChange) return;
 ...
}

do app（Quickie）and it works fine。

I have just implemented this in my to-do app (Quickie) and it works fine.

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