获取将在 UITableView 中插入的行的索引

Posted 2023-02-27

【中文标题】获取将在 UITableView 中插入的行的索引

【英文标题】：get the index of the row that will be inserted in UITableView

【发布时间】：2015-08-11 07:20:56

【问题描述】：

我想要在 UITableView 中仅显示 10 个项目，这很容易使用 [fetchRequest setFetchLimit:10]; 但在插入第 11 个之后item 第一个元素不应再在 UITableView 中可见，元素总数应始终为 10 我已经对这个主题进行了很多研究，我只发现 Get Selected index of UITableView 所以我需要得到什么检查是否行的索引大于 10 删除第 9 个元素这里是所需的完整代码：

#import "ReservationHistoryTableViewController.h"
#import "CoreData.h"
#import "ReservationEntity.h"
#import "EntryCell.h"
#import "DetailedHistoryViewController.h"
@interface ReservationHistoryTableViewController () <NSFetchedResultsControllerDelegate>


@property (strong, nonatomic) NSFetchedResultsController *fetchedResultController ;

@end

@implementation ReservationHistoryTableViewController

- (IBAction)refresh:(id)sender 

    [self getAllReservationHistory];
    [sender endRefreshing];








- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath 
    static NSString *cellIdentifier =  @"Cell";
    EntryCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier forIndexPath:indexPath];
    ReservationEntity *reservationEntry  = [self.fetchedResultController objectAtIndexPath:indexPath];
    [cell configureCellForEntry:reservationEntry];

    return cell;








-(NSFetchRequest *) entryListFetchRequest 
    NSFetchRequest *fetchRequest  = [NSFetchRequest fetchRequestWithEntityName:@"Reservations"];
    [fetchRequest setFetchLimit:10];
    [self.tableView reloadData];
    fetchRequest.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"reservationID" ascending:NO]];
    return fetchRequest;




// this method is used to fetch the data //
-(NSFetchedResultsController *) fetchedResultController 
    if(_fetchedResultController != nil)
        return _fetchedResultController;
    CoreData *coreDataStack = [CoreData defaultStack];
    NSFetchRequest *fechtRequest = [self entryListFetchRequest];
    _fetchedResultController = [[NSFetchedResultsController alloc] initWithFetchRequest:fechtRequest managedObjectContext:coreDataStack.managedObjectContext sectionNameKeyPath:nil cacheName:nil];
    _fetchedResultController.delegate = self;
    return _fetchedResultController;






-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender

    if([segue.identifier isEqualToString:@"details"])
    
        UITableViewCell *cell = sender;
        NSIndexPath *indexPath = [self.tableView indexPathForCell:cell];
        UINavigationController *naviagationController = segue.destinationViewController;
        DetailedHistoryViewController *detailedHisotryViewController = (DetailedHistoryViewController *) naviagationController.topViewController;
        detailedHisotryViewController.entry = [self.fetchedResultController objectAtIndexPath:indexPath];
    





-(void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath

    switch (type) 
        case NSFetchedResultsChangeInsert:

//            NSIndexPath *selectedIndexPath = [self. indexPathForSelectedRow];



            if(newIndexPath.section > 10)
            
                [self.tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationAutomatic];
                [self.tableView deleteRowsAtIndexPaths:@[@(9)] withRowAnimation:UITableViewRowAnimationAutomatic];
// even i try if(newIndexPath.row) i could not reach my target // 

            


            else
            
                [self.tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationAutomatic];
            

            break;
        default:
            break;
    

【参考方案1】：

你走错了方向。 NSIndexPath 是用来识别行和节的，但你使用的是 CoreData，你不应该自己做这种类型的逻辑让你的生活复杂化。

正确的解决方案是根据 Apple 指南实施 NSFetchedResultsController（您可以复制并粘贴）：

- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller 
    // The fetch controller is about to start sending change notifications, so prepare the table view for updates.
    [self.tableView beginUpdates];



- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath 

    UITableView *tableView = self.tableView;

    switch(type) 

        case NSFetchedResultsChangeInsert:
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;

        case NSFetchedResultsChangeDelete:
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;

        case NSFetchedResultsChangeUpdate:
            [self configureCell:[tableView cellForRowAtIndexPath:indexPath] atIndexPath:indexPath];
            break;

        case NSFetchedResultsChangeMove:
           [tableView deleteRowsAtIndexPaths:[NSArray
arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
           [tableView insertRowsAtIndexPaths:[NSArray
arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
           break;
    



- (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id )sectionInfo atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type 

    switch(type) 

        case NSFetchedResultsChangeInsert:
            [self.tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
            break;

        case NSFetchedResultsChangeDelete:
            [self.tableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
            break;
    



- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller 
    // The fetch controller has sent all current change notifications, so tell the table view to process all updates.
    [self.tableView endUpdates];

为了删除你应该做的对象：

[coreDataStack.managedObjectContext deleteObject:object];

用于插入对象：

[coreDataStack.managedObjectContext insertObject:object];

您也可以只插入对象 - 如果它属于 NSFetchedResultsController NSFetchRequest 条款 - 它将自动为您重新获取，您的视图将通过我在上面粘贴的委托方法获得通知。

【讨论】：

我怎么知道tableView里面的元素个数是10？

NSFetchedResultsController 将采用这些。它在所有这些插入/删除操作期间保持结果同步 - 如果它应该重新获取因为插入了某些东西 - 它会自动执行此操作并通知您委托。您只需要确保您插入的对象实际上属于 NSFetchRequest 排序和限制条款 - 在您的情况下设置正确的 reservationID。

我只提到了一个断点：case NSFetchedResultsChangeMove: [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade]; [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];休息;我注意到这种情况从未发生过

如果您不删除属于结果集的对象 - 它不会

忘记告诉你，当从核心数据中获取数据时，我能够得到最后十条记录，这就是我想要的，但是当我插入一个新行并且项目是 10 时UITableView 最后一项应该被删除并应该插入新的让我们举这个例子 10 9 8 7 6 5 4 3 2 1 当插入 11 时它应该是这样的 11 10 9 8 7 6 5 4 3 2 抱歉因为我的英语不好，我想现在对你来说更清楚了，提前谢谢