UITableView 行删除崩溃应用

Question

我有一个基于 Core Data 的表视图，它有一个简单的删除方法。这是可以在无数教程中找到的简单代码，但是，它会使应用程序崩溃并显示以下消息：

Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Invalid update: invalid number of rows in section 0. The number of rows contained in an existing section after the update (2) must be equal to the number of rows contained in that section before the update (2), plus or minus the number of rows inserted or deleted from that section (0 inserted, 1 deleted) and plus or minus the number of rows moved into or out of that section (0 moved in, 0 moved out).'

删除方法如下：

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


    if (editingStyle == UITableViewCellEditingStyleDelete) {

        // get garden to delete, delete it through Core Data


        Garden *gardenToDelete = [self.fetchedResultsController objectAtIndexPath:indexPath];
        NSLog(@"Garden name: %@", gardenToDelete.gardenName);

        [self.managedObjectContext deleteObject:gardenToDelete];
        [self.managedObjectContext save:nil];

        [self.tableView beginUpdates];

        [self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationRight];

        [self.tableView endUpdates];
        }
}

我花了几个小时重新排列代码，删除 beginUpdate 和 endUpdate 调用，检查其他解决方案。非常感谢您的帮助。

Answer 1

您只需要从您的NSFetchedResultsController 中删除该对象，然后假设您已实现docs 中描述的委托方法，获取的结果控制器将更新表格视图。您不应该触摸表格视图行，NSFetchedResultsControllerDelegate 会完成所有这些操作。

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

  if (editingStyle == UITableViewCellEditingStyleDelete) {

      // deleting cell from fetched results contoller

      Garden *gardenToDelete = [self.fetchedResultsController objectAtIndexPath:indexPath];
      NSLog(@"Garden name: %@", gardenToDelete.gardenName); 
      [self.managedObjectContext deleteObject:gardenToDelete];
      [self.managedObjectContext save:nil];
  }
}

Answer 2

您是否使用NSFetchedResultsController 的返回值实现- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section？保存后self.fetchedResultsController会刷新，但要确保tableView返回值的dataSource全部依赖self.fetchedResultsController。

Answer 3

你是否实现了这些方法：

 - (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;

// my comment: mapIndexPathFromFetchResultsController function, I just use to get indexPath. You can remove it 
indexPath = [self mapIndexPathFromFetchResultsController:indexPath];
newIndexPath = [self mapIndexPathFromFetchResultsController:newIndexPath];

switch(type) {
    case NSFetchedResultsChangeInsert:
    {
        [tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
        break;
    }

    case NSFetchedResultsChangeDelete:
    {
        [tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationFade];
        break;
    }

    case NSFetchedResultsChangeUpdate:
    {
        UITableViewCell *cell;
        cell = [tableView cellForRowAtIndexPath:indexPath];
        if (cell != nil)
        {
            // my comment: just use the same with cellForRowAtIndexPath
            // - (void)syncViewConfigureCell:(UITableViewCell *)cell {
            // cell.textLabel.text = @""; etc. }
            [self syncViewConfigureCell:cell];
        }
        break;
    }

    case NSFetchedResultsChangeMove:
    {
        [tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationFade];
        [tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
        break;
    }
}
    }


    - (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id <NSFetchedResultsSectionInfo>)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];
    }