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标题: ios - 使用 NSSortDescriptor 按时间错误排序(带有核心数据) [打印本页]

作者: 菜鸟教程小白 时间: 2022-12-13 04:43
标题: ios - 使用 NSSortDescriptor 按时间错误排序(带有核心数据)

请在这里帮助我。我遇到了一些非常奇怪的错误，试图对我的字符串 TableView 对象进行排序。

行为很简单，我有:

CreateViewController - 我在这里创建字符串并将它们添加到核心数据中

StackTableViewController - 这是我创建的字符串的表格 View 。它们应该按日期排序，第一个单元格是最旧的，第二个单元格是在他之后创建的，依此类推......

HomeViewController - 这里我有一个 UILabel，它一直保存表格 View 的第一个对象，如果我在表格中删除它，我会使用委托(delegate)方法更新这个标签，

原来如此。

问题:

如果表格 View 中没有字符串，然后我在创建页面中添加了一个字符串，它会被很好地创建，但是如果添加另一个，新的字符串会在列表的顶部...但是如果我终止该应用程序并再次打开它的顺序很好。

在我添加更多字符串后还有一些其他奇怪的行为......但问题是，每当我终止应用程序并再次打开它时，一切都完美无缺......:/

这是相关代码:

CreateViewController.m

- (id)init { 
    self = [super initWithNibName"CreateViewController" bundle:nil];
    if (self) {
    }
    return self;
}


- (void)save {

    if (self.myTextView.text.length == 0) {
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle"Hey!" message"You can't save a blank string" delegate:self cancelButtonTitle"Ok" otherButtonTitles:nil, nil];
        [alert show];
    } 

    [self insertTeget];

    [self.presentingViewController dismissViewControllerAnimated:YES completion:nil];

    [self.myTextView resignFirstResponder];
}

//this is where I add the string to the NSManagedObject object I have called 'Target' 
- (void)insertTeget {

    CoreDataStack *stack = [CoreDataStack defaultStack];
    Target *target = [NSEntityDescription insertNewObjectForEntityForName"Target" inManagedObjectContext:stack.managedObjectContext];
    if (self.myTextView.text != nil) {
        target.body = self.myTextView.text;
    }

    [stack saveContext];
}

这是表格 View :

StackTableViewController.m

- (id)init {

    self = [super initWithNibName"StackTableViewController" bundle:nil];
    if (self) {

        [self fetchData];
    }
    return self;
}

//currentTarget is a string I have in the .h file to pass the home view controller the first string of the table view  
- (void)fetchData {
    [self.fetchedResultController performFetch:nil];
    if (self.fetchedResultController.fetchedObjects.count > 0) {
        NSIndexPath *indexPath = [NSIndexPath indexPathForItem:0 inSection:0];
        Target *current = [self.fetchedResultController objectAtIndexPath:indexPath];
        self.currentTarget = current.body;
    }else {
        self.currentTarget = nil;
    }
}

- (void)viewDidLoad {

    [super viewDidLoad];
    [self fetchData];
}

#pragma mark - Table view data source

- (NSInteger)numberOfSectionsInTableViewUITableView *)tableView {
    // Return the number of sections.
    return self.fetchedResultController.sections.count;
}

- (NSInteger)tableViewUITableView *)tableView numberOfRowsInSectionNSInteger)section {
    // Return the number of rows in the section.
    id <NSFetchedResultsSectionInfo> sectionInfo = [self.fetchedResultController sections][section];
    return [sectionInfo numberOfObjects];
}

- (UITableViewCellEditingStyle)tableViewUITableView *)tableView editingStyleForRowAtIndexPathNSIndexPath *)indexPath
{
    return UITableViewCellEditingStyleDelete;
}

//here I'm updating the delegate when A cell was deleted so I can update the label in the home view controller
- (void)tableViewUITableView *)tableView commitEditingStyleUITableViewCellEditingStyle)editingStyle forRowAtIndexPathNSIndexPath *)indexPath {

    Target *target = [self.fetchedResultController objectAtIndexPath:indexPath];
    CoreDataStack *stack = [CoreDataStack defaultStack];
    [[stack managedObjectContext] deleteObject:target] ;
    [stack saveContext];

    if ([_delegate respondsToSelectorselector(didDeleteObject)]) {
        [self fetchData];
        [_delegate didDeleteObject];
    }
}

- (UITableViewCell *)tableViewUITableView *)tableView cellForRowAtIndexPathNSIndexPath *)indexPath {

    static NSString *cellIdentifier = @"StackTableViewCell";

    Target *target = [self.fetchedResultController objectAtIndexPath:indexPath];

    StackTableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];

    if (!cell)
    {
        NSArray *topLevelObjects = [[NSBundle mainBundle] loadNibNamed"StackTableViewCell" owner:self options:nil];
        cell = [topLevelObjects objectAtIndex:0];
    }

    cell.cellLabel.text = target.body;

    return cell;
}

// this is my fetch request where im setting up the sort descriptor 
- (NSFetchRequest *)targetsFetchRequest {

    NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName"Target"];
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey"time" ascending:YES];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
    [fetchRequest setSortDescriptors:sortDescriptors];
    return fetchRequest;
}


- (NSFetchedResultsController *)fetchedResultController {

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

    CoreDataStack *stack = [CoreDataStack defaultStack];

    NSFetchRequest *fetchRequest = [self targetsFetchRequest];

    _fetchedResultController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:stack.managedObjectContext sectionNameKeyPath:nil cacheName:nil];

    _fetchedResultController.delegate = self;

    return _fetchedResultController;

}

这是我更新标签的主视图 Controller :

- (id)init {
    self = [super initWithNibName:@"HomeViewController" bundle:nil];
    if (self) {
        stackTableViewController = [[StackTableViewController alloc] init];
        stackTableViewController.delegate = self;
    }
    return self;
}


- (void)viewWillAppear:(BOOL)animated {
    [stackTableViewController fetchData];
    self.homeLabel.text = stackTableViewController.currentTarget;
}

- (void)viewDidLoad {

    [super viewDidLoad];
    self.homeLabel.text = stackTableViewController.currentTarget;
}

//this is the delegate method
- (void)didDeleteObject { 
    self.homeLabel.text = stackTableViewController.currentTarget;
}

- (IBAction)goToStack:(id)sender {

    [self.navigationController pushViewController:stackTableViewController animated:YES];
}

- (IBAction)goToCreate:(id)sender {

    CreateViewController *createViewController = [[CreateViewController alloc]initWithNibName:@"CreateViewController" bundle:nil];
    UINavigationController *navigationController = [[UINavigationController alloc]initWithRootViewController:createViewController];
    [self.navigationController presentViewController:navigationController animated:YES completion:nil]}

拜托拜托，这让我发疯了，为什么只有在我终止应用程序后订单才能正常？谢谢@@@!

Best Answer-推荐答案

我没有看到你在任何地方设置时间。当您创建对象时，它应该设置为 [NSDate date]，如果它充当创建日期。

关于ios - 使用 NSSortDescriptor 按时间错误排序(带有核心数据)，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/27863393/

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