Question

这是我的控制器类的接口：

@interface ProjectListViewController : UITableViewController <NSFetchedResultsControllerDelegate> {
    NSFetchedResultsController *fetchedResultsController;
    NSManagedObjectContext *managedObjectContext;
}

@end

我使用以下代码初始化 fetchedResultsController ：

if (fetchedResultsController != nil) {
    return fetchedResultsController;
}

    // Create and configure a fetch request with the Project entity.
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Project" inManagedObjectContext:managedObjectContext];
    [fetchRequest setEntity:entity];

    // Create the sort descriptors array.
    NSSortDescriptor *projectIdDescriptor = [[NSSortDescriptor alloc] initWithKey:@"projectId" ascending:YES];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:projectIdDescriptor, nil];
    [fetchRequest setSortDescriptors:sortDescriptors];

    // Create and initialize the fetch results controller.
    NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest 
                                                                                            managedObjectContext:managedObjectContext 
                                                                                              sectionNameKeyPath:nil 
                                                                                                       cacheName:nil];
    self.fetchedResultsController = aFetchedResultsController;
    fetchedResultsController.delegate = self;

如您所见，我使用的是我的控制器类中定义的 managedObjectContext

这是采用NSFetchedResultsControllerDelegate协议：

- (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:(TDBadgedCell *)[tableView cellForRowAtIndexPath:indexPath] atIndexPath:indexPath];
                break;

            case NSFetchedResultsChangeMove:
                if (newIndexPath != nil) {
                    [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
                    [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
                }
                else {
                    [tableView reloadSections:[NSIndexSet indexSetWithIndex:indexPath.section] 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 {
        [self.tableView endUpdates];
}

在_configureCell：atIndexPath：方法内部我有以下代码：

    NSFetchRequest *issuesNumberRequest = [NSFetchRequest new];
    NSEntityDescription *issueEntity = [NSEntityDescription entityForName:@"Issue" inManagedObjectContext:managedObjectContext];
    [issuesNumberRequest setEntity:issueEntity];
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"projectId == %@", project.projectId];
    [issuesNumberRequest setPredicate:predicate];
    NSUInteger issuesNumber = [managedObjectContext countForFetchRequest:issuesNumberRequest error:nil];
    [issuesNumberRequest release];

我再次使用managedObjectContext。

但是当我尝试插入新项目时，应用程序崩溃并出现以下异常：

断言失败 - [UITableView _endCellAnimationsWithContext：]，/ SourceCache / UIKit_Sim / UIKit-984.38 / UITableView.m：774 由于未被捕获而终止应用程序例外 'NSInternalInconsistencyException'，原因：'无效更新：无效第0节中的行数一个包含的行数更新后的现有部分（4）必须等于行数包含在该部分之前更新（4），加号或减号从中插入或删除的行数部分（1个插入，0个删除）。'

幸运的是，我找到了一个解决方法：如果我在_configureCell中创建并使用单独的NSManagedObjectContext：atIndexPath：方法应用程序不会崩溃！

我只想知道，这种行为是否正确？

Here is a sample project. 请注意CrashMeViewController的'_configureCell：atIndexPath：'和'_addSomeRows'方法

Answer 1

已在iOS 4.0中修复

NSFetchedResultsController：在更新期间使用NSManagedObjectContext会导致崩溃

1 个答案: