如何在 cellEdit 之后强制从持久存储重新加载核心数据

Question

编辑单元格后，我无法从核心数据持久存储重新加载数据。

我尝试重新加载 tableView 本身，但这不会强制从持久存储中获取，我该如何强制重新加载？

这是我重新加载的尝试，但如果我退出 UIViewController 并返回所有工作，那么我知道持久存储已正确更新

- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath
{

    AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication]delegate];

    NSManagedObjectContext *context = appDelegate.persistentContainer.viewContext;

    if([NWTillHelper isDebug] == 1) {
        NSLog(@"TransactionListView:tableView:context = %@", context);
    }

    if (editingStyle == UITableViewCellEditingStyleDelete) {

        NSManagedObject *transactionRow = [self.transactionRowsRows objectAtIndex:indexPath.row];

        [transactionRow setValue:[NSNumber numberWithInt:[@"999" intValue]] forKey:@"status"];
        [transactionRow setValue:[NSNumber numberWithInt:[@"0" intValue]] forKey:@"qty"];
        [transactionRow setValue:[NSDecimalNumber decimalNumberWithString:@"0"] forKey:@"price"];
        [transactionRow setValue:[NSDecimalNumber decimalNumberWithString:@"0"] forKey:@"discountPercentage"];
        [transactionRow setValue:[NSDecimalNumber decimalNumberWithString:@"0"] forKey:@"discountAmount"];
        [transactionRow setValue:[NSDecimalNumber decimalNumberWithString:@"0"] forKey:@"amountTax"];
        [transactionRow setValue:[NSDecimalNumber decimalNumberWithString:@"0"] forKey:@"sum"];

        NSError *error = nil;
        if (![context save:&error]) {
            if([NWTillHelper isDebug] == 1) {
                NSLog(@"Can't Delete! %@ %@", error, [error localizedDescription]);
                return;
            }
        }
        [self.transactionListViewTbl reloadData];
    }
}

Answer 1

只是想提一下。

阅读您的问题后，我觉得它不会使用 Fetch Controller 来修复。 Fetch Controller 非常简洁，它可以让您保持表格更新，而无需显式调用 [table reloadData]。但是，如果重新加载您的表数据没有得到更新，您可能有多个托管对象上下文更新您的持久存储。

数据由不同的托管对象上下文更新，并且您没有在连接表的那个上下文中获得更新。我将从查看我的核心数据堆栈和托管对象上下文的数量开始。如果您需要超过 1 个，您可以订阅更改，或者确保您希望看到的更改是在同一个托管对象上下文中完成的。

希望对你有帮助。

Managed Object Context - Apple Docs

Answer 2

使用 NSFetchedResultsController 作为数据源并实现 NSFecthedResultsController 委托

您可以在 viewController 中创建 NSFetchedResults 控制器作为属性，创建它的单个实例

lazy var transactionFetchedResultsController : NSFetchedResultsController<Transaction> = {
        let appdelegate = UIApplication.shared.delegate as! AppDelegate
        var fetchedResultsController : NSFetchedResultsController< Transaction >!

        appdelegate.managedObjectContext.performAndWait {
            var fetchRequest: NSFetchRequest< Transaction >
            if #available(iOS 10.0, *) {
                fetchRequest = Transaction.fetchRequest()
            } else {
                fetchRequest  = NSFetchRequest(entityName: "Transaction")
            }

            fetchRequest.sortDescriptors = [NSSortDescriptor(key: "your_property", ascending: true)]
            let yourPredicate = NSPredicate(format: "your condition == whatever")
            fetchRequest.predicate = yourPredicate
            fetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: appdelegate.managedObjectContext, sectionNameKeyPath: nil, cacheName: nil)
        }
        return fetchedResultsController
    }()

为您的 viewController 设置委托

self. transactionFetchedResultsController.delegate = self

最后在viewDidLoad()中初始化

try! self. transactionFetchedResultsController.performFetch()

现在实现委托:)

extension YourViewController : NSFetchedResultsControllerDelegate{
    func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) {
        //row updated
    }

    func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange sectionInfo: NSFetchedResultsSectionInfo, atSectionIndex sectionIndex: Int, for type: NSFetchedResultsChangeType) {
        //section updated
    }

    func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        //change completed
        //reload your tableView
    }
}

编辑

如果您想知道如何使用 NSFetchedResultsController 作为 tableView 数据源？

extension YourViewController: UITableViewDataSource {
    func numberOfSections(in tableView: UITableView) -> Int {
        return (self. transactionFetchedResultsController.sections?.count)!
    }

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
           //assuming you have only one section
           //you can always return number of items in each section using NSFetchedResultsController :)
            return (self. transactionFetchedResultsController.fetchedObjects?.count)!
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        //let cell = ....
        //you can instantiate your cell here
        //you can access your transaction as below
        let transaction = self. transactionFetchedResultsController.fetchedObjects![indexPath.row]
        //return your cell
        return cell
    }
}

希望对你有帮助:)