iphone - NSFetchedResultsController 的委托(delegate)方法处理

Question

我有 UITableView 和 NSFetchedResultsController 附加到它。 FRC 的委托(delegate)方法完美运行，一切都很好，但我的单元格具有取决于单元格位置的自定义背景:1. 在 UITableView 的顶部(顶部有圆角的背景)2.在中间(没有圆角的背景)3.在底部(底部有圆角的背景)4. 单格(所有角都是圆的)。在我的单元格配置方法中，我计算了单元格的位置，并为其设置了适当的背景 View 。一切正常，但是FRC的delegate方法的实现出现了问题:

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

    UITableView *tableView =  self.agenciesTableView;

    switch(type)
    {
        case NSFetchedResultsChangeInsert:
        {
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath]
                             withRowAnimation:UITableViewRowAnimationNone];
            break;
        }
        case NSFetchedResultsChangeDelete:
        {
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath]
                             withRowAnimation:UITableViewRowAnimationNone];
            break;
        }
        case NSFetchedResultsChangeUpdate:
        {
            [tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];

            break;
        }
        case NSFetchedResultsChangeMove:
        {

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

如您所见，这很常见，但有一个问题:如果单元格被插入到 UITableView 的顶部，它的配置方法 (cellForRowAtIndexPath) 被调用并且它正确绘制(带有圆顶角)但是它下面的单元格(以前在顶部)仍然带有圆顶角和我需要以某种方式重新绘制它。

-=已编辑=-

我更改了 FRC 的委托(delegate)方法以反射(reflect)更新逻辑:

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

    UITableView *tableView =  self.agenciesTableView;

    switch(type)
    {
        case NSFetchedResultsChangeInsert:
        {
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath]
                             withRowAnimation:UITableViewRowAnimationNone];

            //if we inserting a cell not to the middle of table view
            //we need to update the previous cell (if we are inserting to the end)
            // or the next cell (if we are inserting to the beggining)
            if ([self controller:controller positionForCellAtIndexPath:newIndexPath]!=UITableViewCellPositionMiddle)
            {
                NSIndexPath *prevIndexPath=[NSIndexPath indexPathForRow:(newIndexPath.row+1) inSection:newIndexPath.section];
                NSIndexPath *nextIndexPath=[NSIndexPath indexPathForRow:(newIndexPath.row-1) inSection:newIndexPath.section];
                if ([self controller:controller cellExistsAtIndexPath:prevIndexPath])
                {
                    [tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:prevIndexPath] withRowAnimation:UITableViewRowAnimationNone];
                };
                if ([self controller:controller cellExistsAtIndexPath:nextIndexPath])
                {
                    [tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:nextIndexPath] withRowAnimation:UITableViewRowAnimationNone];
                };
            };
            break;
        }
        case NSFetchedResultsChangeDelete:
        {
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath]
                             withRowAnimation:UITableViewRowAnimationNone];

            //if we deleting a cell not fromo the middle of table view
            //we need to update the previous cell (if we are deleting from the end)
            //or the next cell (if we are deleting from the beggining)
            if ([self controller:controller positionForCellAtIndexPath:indexPath]!=UITableViewCellPositionMiddle)
            {
                NSIndexPath *prevIndexPath=[NSIndexPath indexPathForRow:(indexPath.row+1) inSection:indexPath.section];
                NSIndexPath *nextIndexPath=[NSIndexPath indexPathForRow:(indexPath.row-1) inSection:indexPath.section];
                if ([self controller:controller cellExistsAtIndexPath:prevIndexPath])
                {
                    [tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:prevIndexPath] withRowAnimation:UITableViewRowAnimationNone];
                };
                if ([self controller:controller cellExistsAtIndexPath:nextIndexPath])
                {
                    [tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:nextIndexPath] withRowAnimation:UITableViewRowAnimationNone];
                };
            };
            break;
        }
        case NSFetchedResultsChangeUpdate:
        {
            [tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationNone];

            break;
        }
        case NSFetchedResultsChangeMove:
        {

            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath]
                             withRowAnimation:UITableViewRowAnimationNone];
            if ([self controller:controller positionForCellAtIndexPath:indexPath]!=UITableViewCellPositionMiddle)
            {
                NSIndexPath *prevIndexPath=[NSIndexPath indexPathForRow:(indexPath.row+1) inSection:indexPath.section];
                NSIndexPath *nextIndexPath=[NSIndexPath indexPathForRow:(indexPath.row-1) inSection:indexPath.section];
                if ([self controller:controller cellExistsAtIndexPath:prevIndexPath])
                {
                    [tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:prevIndexPath] withRowAnimation:UITableViewRowAnimationNone];
                };
                if ([self controller:controller cellExistsAtIndexPath:nextIndexPath])
                {
                    [tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:nextIndexPath] withRowAnimation:UITableViewRowAnimationNone];
                };
            };


            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath]
                             withRowAnimation:UITableViewRowAnimationNone];
            if ([self controller:controller positionForCellAtIndexPath:newIndexPath]!=UITableViewCellPositionMiddle)
            {
                NSIndexPath *prevIndexPath=[NSIndexPath indexPathForRow:(newIndexPath.row+1) inSection:newIndexPath.section];
                NSIndexPath *nextIndexPath=[NSIndexPath indexPathForRow:(newIndexPath.row-1) inSection:newIndexPath.section];
                if ([self controller:controller cellExistsAtIndexPath:prevIndexPath])
                {
                    [tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:prevIndexPath] withRowAnimation:UITableViewRowAnimationNone];
                };
                if ([self controller:controller cellExistsAtIndexPath:nextIndexPath])
                {
                    [tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:nextIndexPath] withRowAnimation:UITableViewRowAnimationNone];
                };
            };
            break;
        }
    };
}

但在这种情况下我得到一个错误:

2013-05-24 21:04:19.458 PharmaTouch[6994:fb03] *** Assertion failure in -[_UITableViewUpdateSupport _computeRowUpdates], /SourceCache/UIKit_Sim/UIKit-  1912.3/UITableViewSupport.m:386
2013-05-24 21:04:19.483 PharmaTouch[6994:fb03] CoreData: error: Serious application error.  An exception was caught from the delegate of NSFetchedResultsController during a call to -controllerDidChangeContent:.  Invalid table view update.  The application has requested an update to the table view that is inconsistent with the state provided by the data source. with userInfo (null)

-=EDITED2=-这是我的 controller:cellExistsAtIndexPath: 方法实现。它用于安全检查，以避免使用超出范围的 indexPath 参数调用 reloadRowsAtIndexPaths。

-(BOOL)controller:(NSFetchedResultsController *)controller cellExistsAtIndexPath:(NSIndexPath *)indexPath
{
    if (indexPath.row<0)
    {
        return NO;
    };

    NSInteger numberOfRows = 0;
    NSArray *sections = controller.sections;
    if(sections.count > 0)
    {
        id <NSFetchedResultsSectionInfo> sectionInfo = [sections objectAtIndex:indexPath.section];
        numberOfRows = [sectionInfo numberOfObjects];
    };
    if (indexPath.row>(numberOfRows-1))
    {
        return NO;
    }
    else
    {
        return YES;
    };
}

Answer 1

当您使用 UITableViewRowAnimationNone 时，您也可以只使用 reloadData 然后它会正确完成，因为所有行都将被刷新。

在你使用 UITableViewRowAnimationFade 的地方，考虑一下你对它的重视程度......

您需要在检查和重新加载方面更加全面。特别是，您需要从 FRC 获取正在更改的部分的部分信息。如果传入或传出行是第一行或最后一行，则需要刷新多行。沿着:

if first is changing and count > 1, also refresh second
if last is changing and count > 1, also refresh first