NSFetchedResultsController帮助

Question

我的表视图没有显示任何内容(即使有数据)，当我从选项卡栏切换回它时，会得到一个错误：

2011-06-28 11:25:20.043狗仔队7773:207个-__NSCFArray区段:未识别的选择器发送到实例0x592d2d0 2011-06-28 11:25:20.048狗仔队7773:207*终止应用程序由于非正常异常'NSInvalidArgumentException'，原因：‘_NSCFArray区段:未识别的选择器发送到实例0x592d2 d0’

我做错了什么？

您可以在以下位置获得完整的代码：

https://github.com/blasto333/Paparazzi

标题

@interface PersonListViewController : UITableViewController {
    NSFetchedResultsController *fetchResultsController;
}

@end

实现

- (void)viewDidLoad
{
    [super viewDidLoad];

    // Uncomment the following line to preserve selection between presentations.
    // self.clearsSelectionOnViewWillAppear = NO;

    // Uncomment the following line to display an Edit button in the navigation bar for this view controller.
    // self.navigationItem.rightBarButtonItem = self.editButtonItem;

    fetchResultsController = [[FlickrFetcher sharedInstance] fetchedResultsControllerForEntity:@"Person" withPredicate:nil];
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
}

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
}

- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
}

- (void)viewDidDisappear:(BOOL)animated
{
    [super viewDidDisappear:animated];
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

#pragma mark - Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    return [[fetchResultsController sections] count];
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    id <NSFetchedResultsSectionInfo> sectionInfo = [[fetchResultsController sections] objectAtIndex:section];
    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] autorelease];
    }

    // Configure the cell...
    Person *person = [fetchResultsController objectAtIndexPath:indexPath];
    [cell.textLabel setText:person.name];

    return cell;
}

Answer 1

您需要保留fetchResultsController，因为它一创建就会发布。方法fetchedResultsControllerForEntity:withPredicate返回一个自动释放的对象。将行改为：

fetchResultsController = [[[FlickrFetcher sharedInstance] fetchedResultsControllerForEntity:@"Person" withPredicate:nil] retain];

然而，iOS和Mac上的内存管理将很快成为过去。如果您是付费ADC成员，请查看Xcode的一些beta版本，并测试驱动自动参考计数的内容。我已经用了几个星期了，效果很好。

编辑:因为您的fetchResultsController中没有任何数据，所以不会显示任何行。方法numberOfSectionsInTableView:正在返回零，因此您的TableViewDataSource协议的其他方法都没有被调用。