numberOfRowsInSection:核心数据和多节的方法 [英] numberOfRowsInSection: method for core data and multiple sections

问题描述

我正在尝试显示一个包含 2 个部分的表格视图.第一部分将始终有 1 行，第二部分将有与数据点一样多的行.我正在使用核心数据和以下 tableView:numberOfRowsInSection: 方法...

I am trying to show a table view with 2 sections. The first section will always have 1 row and the second section will have as many rows as data points. I am using Core Data and the following tableView:numberOfRowsInSection: method...

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    if (section == 0) {
        return 1;
    } else {
        id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section];
        return [sectionInfo numberOfObjects];
    }
}

但是，我收到以下错误:

However, I am getting the following error:

由于未捕获的异常NSRangeException"而终止应用，原因:'* -[__NSArrayM objectAtIndex:]: 索引 1 超出范围 [0 .. 0]'

Terminating app due to uncaught exception 'NSRangeException', reason: '* -[__NSArrayM objectAtIndex:]: index 1 beyond bounds [0 .. 0]'

任何帮助将不胜感激.谢谢.

Any help will be appreciated. Thanks.

新 -------------------------------------------------------------------------------

NEW -------------------------------------------------------------------------------

这是相关方法的当前实现:

This is the current implementation of the relevant methods:

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    if (section == 0) {
        return 1;
    } else {
        NSUInteger frcSection = section - 1;
        id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:frcSection];
        return [sectionInfo numberOfObjects];
    }
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

    if (cell == nil) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
    }

    [self configureCell:cell atIndexPath:indexPath];
    return cell;
}

- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath
{
    if (indexPath.section == 0) {
        cell.textLabel.text = entityOne.name;  //entityOne object passed from previous VC
    } else {
        entityTwo = [self.fetchedResultsController objectAtIndexPath:indexPath];
        cell.textLabel.text = entityTwo.name;
    }
}

- (void)controller:(NSFetchedResultsController *)controller
  didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo
           atIndex:(NSUInteger)sectionIndex
     forChangeType:(NSFetchedResultsChangeType)type
{
    NSUInteger frcSectionIndex = 0;
    frcSectionIndex = sectionIndex + 1;

    switch(type) {
        case NSFetchedResultsChangeInsert:
            [self.tableView insertSections:[NSIndexSet indexSetWithIndex:frcSectionIndex] withRowAnimation:UITableViewRowAnimationFade];
            break;

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

- (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:@[newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;

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

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

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

推荐答案

原因是 fetched results controller (FRC) 只有一个部分(section #0)，你想要的显示在表格视图的第二部分(部分 #1)中.

The reason is that the fetched results controller (FRC) has only one section (section #0), which you want to be displayed in the second section (section #1) of the table view.

这是可能的，但是您必须在 FRC 部分编号和表视图部分编号之间进行映射，例如

This is possible, but you have to map between FRC section numbers and table view section numbers, e.g.

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    if (section == 0) {
        return 1;
    } else {
        NSUInteger frcSection = section - 1;
        id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:frcSection];
        return [sectionInfo numberOfObjects];
    }
}

cellForRowAtIndexPath 中需要相同的映射.

在 FRC 委托方法 didChangeObject、didChangeSection 中，您必须在调用表视图方法(例如 <代码>insertRowsAtIndexPaths).

In the FRC delegate methods didChangeObject, didChangeSection you have to add 1 to the section number before calling the table view methods (e.g. insertRowsAtIndexPaths).

添加: configureCell 应该如下所示:

- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath
{
    if (indexPath.section == 0) {
        cell.textLabel.text = entityOne.name;  //entityOne object passed from previous VC
    } else {
        NSIndexPath *frcIndexPath = [NSIndexPath indexPathForRow:indexPath.row inSection:(indexPath.section - 1)];
        entityTwo = [self.fetchedResultsController objectAtIndexPath:frcIndexPath];
        cell.textLabel.text = entityTwo.name;
    }
}

和 didChangeObject 像这样:

- (void)controller:(NSFetchedResultsController *)controller
   didChangeObject:(id)anObject
       atIndexPath:(NSIndexPath *)indexPath
     forChangeType:(NSFetchedResultsChangeType)type
      newIndexPath:(NSIndexPath *)newIndexPath
{
    UITableView *tableView = self.tableView;
    NSIndexPath *tvIndexPath = [NSIndexPath indexPathForRow:indexPath.row inSection:(indexPath.section + 1)];
    NSIndexPath *tvNewIndexPath = [NSIndexPath indexPathForRow:newIndexPath.row inSection:(newIndexPath.section + 1)];

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

        case NSFetchedResultsChangeDelete:
            [tableView deleteRowsAtIndexPaths:@[tvIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;

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

        case NSFetchedResultsChangeMove:
            [tableView deleteRowsAtIndexPaths:@[tvIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            [tableView insertRowsAtIndexPaths:@[tvNewIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;
    }
}

你可能明白了:

• 当从 FRC 索引路径转到表视图索引路径时，在节中添加一个.
• 当从表视图索引路径转到 FRC 索引路径时，从节中减去一个.

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