問題描述

在使用 Core Data 作為后備存儲的 UITableViewController 中實現用戶定義的排序需要執行哪些步驟?

What are the steps that I need to perform to implement user-defined ordering in a UITableViewController with Core Data as the backing store?

我還需要響應 -tableView:moveRowAtIndexPath:fromIndexPath:toIndexPath: 還是模型重新排序由表視圖自動處理?我可以只選中 Core Data 模型文件中的Ordered"復選框并期望它將更改從 table view 傳輸到 store，還是我必須做更多?我是否必須更改 fetchedResultsController 獲取其對象的方式(例如添加排序描述符)?

Do I still need to respond to -tableView:moveRowAtIndexPath:fromIndexPath:toIndexPath: or is the model re-ordering handled automatically by the table view? Can I just check the "Ordered" checkbox in the Core Data model file and expect it to transmit the changes from the table view to the store, or do I have to do more? Do I have to change the way my fetchedResultsController gets it's objects (e.g. add a sort descriptor)?

推薦答案

你不需要放棄 NSFetchedResultsController 或 NSOrderedSet.如果您堅持使用 NSOrderedSet，那么簡單的方法就是向您的對象 NSManagedObject 子類添加一個方法.因此，例如，如果您有一個包含有序章節集的對象 Book，您可以向章節對象添加一個方法:

You don't need to abandon NSFetchedResultsController or NSOrderedSet. If you stick with NSOrderedSet, the easy way is to just add a method to your objects NSManagedObject subclass. So for instance, if you have an object Book with an ordered set of Chapters, you can add a method to the Chapters object:

- (NSUInteger)indexInBookChapters
{
    NSUInteger index = [self.book.chapters indexOfObject:self];
    return index;
}

提示:將此添加到一個類別中，這樣它就不會被 CoreData 自動生成的代碼覆蓋.

Tip: Add this to a category so it doesn't get overwritten by CoreData auto generated code.

然后你可以在你的 NSFetchedResultsController 的排序描述符中使用這個方法:

Then you can use this method in your sort descriptor for your NSFetchedResultsController:

fetchRequest.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"indexInBookChapters" ascending:YES]];

這篇關于使用 UITableView 和 NSOrderedSet 對核心數據進行排序的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！