NSFetchedResultsController W/自定义表单元格不兼容指针

Question

我一直在努力掌握CoreData。在几次尝试找到一个好的教程后，我在youtube上的教程取得了很大的进展。然而，当我到达NSFetchedResultsController时，我在自定义表单元格ITDContactCell *cell = [tableView cellForRowAtIndexPath:indexPath]上收到一条警告，指出它是一个用UITableViewCell初始化的不兼容指针（本教程不使用自定义单元格）。

更糟糕的是，当我试图添加一个项目时，我会遇到这个漂亮而丑陋的错误。

2013-12-04 19:15:48.407 Ping〔490:60b〕*断言失败-[UTableView_endCellAnimationsWithContext:]，/SourceCache/UIKit/UIKit-2903.23/UITableView.m:1138 2013-12-0419:15:48.409 Ping[490:60b]核心数据：错误：严重的应用程序错误。从的委托中捕获到异常调用期间的NSFetchedResultsController-controllerIDChangeContent:。尝试将行0插入到节0中，但在使用userInfo更新后，节0中只有0行（空）

我花了几个小时试图弄清楚我做错了什么，但我无法理解。所以，如果有人能看看我的代码，并就如何修复它给我建议，我将不胜感激。谢谢。

控制器：

-(void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath {
    UITableView *tableView = self.ContactsListTableView;
    switch (type) {
        case NSFetchedResultsChangeInsert:
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;
        case NSFetchedResultsChangeDelete:
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;
        case NSFetchedResultsChangeUpdate: {
            Contact *changeContact = [self.fetchedResultsController objectAtIndexPath:indexPath];
            ITDContactCell *cell = [tableView cellForRowAtIndexPath:indexPath];
            cell.name.text = [NSString stringWithFormat:@"%@ %@", changeContact.contactFirstName, changeContact.contactLastName];
        }
            break;
        case NSFetchedResultsChangeMove:
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObjects:newIndexPath, nil] withRowAnimation:UITableViewRowAnimationFade];
            break;
    }
}

编辑：我实现的行数和节数。

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

fetchedResultsController在接口中被简单地定义为@property (strong, nonatomic) NSFetchedResultsController *fetchedResultsController

Answer 1

警告是指方法

[tableView cellForRowAtIndexPath:indexPath];

返回一个UITableViewCell，它实际上不是您的ITDContactCell。在方法之前放置强制转换应删除警告。

ITDContactCell *cell = (ITDContactCell*) [tableView cellForRowAtIndexPath:indexPath];

另一个错误可能是由于fetchedResultsController和tableView之间缺乏关系。显示tableView委托和源方法会有所帮助。我想你已经实现了类似的东西：

-(void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    NSError *error = nil;
    if(![self.fetchedResultsController performFetch:&error]) {
        // NSLog(@"Error! %@", error);
    }
}
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return _fetchedResultsController.sections.count;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    id <NSFetchedResultsSectionInfo> secInfo = [[self.fetchedResultsController sections] objectAtIndex:section];
    return [secInfo numberOfObjects];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    static NSString *CellIdentifier = @"Cell";
    ITDContactCell *cell = (ITDContactCell *)[tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    // assign cell content
    return cell;
}
-(NSString *) tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section {
    return [[[self.fetchedResultsController sections] objectAtIndex:section] name];
}
-(NSFetchedResultsController *) fetchedResultsController {
    if(_fetchedResultsController != nil) {
        return _fetchedResultsController;
    }
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"EntityName"
                                              inManagedObjectContext:self.managedObjectContext];
    [fetchRequest setEntity:entity];
    _fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
                                                                    managedObjectContext:self.managedObjectContext
                                                                      sectionNameKeyPath:nil
                                                                               cacheName:nil];
    _fetchedResultsController.delegate = self;
    return  _fetchedResultsController;
}
-(void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
    [self.tableView beginUpdates];
}
-(void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
    [self.tableView endUpdates];
}
-(void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath {
    UITableView *tableView = self.ContactsListTableView;
    switch (type) {
        case NSFetchedResultsChangeInsert:
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;
        case NSFetchedResultsChangeDelete:
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;
        case NSFetchedResultsChangeUpdate: {
            Contact *changeContact = [self.fetchedResultsController objectAtIndexPath:indexPath];
            ITDContactCell *cell = [tableView cellForRowAtIndexPath:indexPath];
            cell.name.text = [NSString stringWithFormat:@"%@ %@", changeContact.contactFirstName, changeContact.contactLastName];
        }
            break;
        case NSFetchedResultsChangeMove:
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObjects:newIndexPath, nil] withRowAnimation:UITableViewRowAnimationFade];
            break;
    }
}

编辑1:

请注意，您不应该在表视图中使用reloadData方法，因为表是在保存对NSManagedObjectContext的更改后重新加载的（通过提取的结果控制器）。

编辑2:

您是NSManagedObjectContext nil吗？