Question

所以这是我第一次使用核心数据，到目前为止它并不是最好的体验。到目前为止，我的应用程序包含两个UITableView控制器和一个ViewController。该应用程序只是要求用户在UIAlert上输入列表的名称，并将其保存到核心数据，并将列表的名称放入第一个tableview。然后，用户单击列表的名称，并将其推送到列表中的内容，该内容为空，因为尚未填充。然后用户填充TableView，因此它会推送到单个视图控制器，您可以在其中输入所有信息并点击保存。我的问题是，当我点击保存时它没有保存，它会回到最后一个UITableView控制器，没有任何东西存在。这是我的第一个问题，我的第二个问题是我希望在视图之间传递数据，因此当用户点击列表时，它会推送到第二个UITableView控制器并在顶部显示列表的名称。我对所有核心数据和关系感到困惑，所以如果有人能帮助我，我会很感激。我将包含我的代码和数据模型。

数据模型

enter image description here First Views .m（列出所有列表的视图）

- (NSManagedObjectContext *)managedObjectContext {
    NSManagedObjectContext *context = nil;
    id delegate = [[UIApplication sharedApplication] delegate];
    if ([delegate respondsToSelector:@selector(managedObjectContext)]) {
        context = [delegate managedObjectContext];
    }
    return context;
}

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

    // Fetch the lists from persistent data store
    NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"List"];
    self.lists = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];
    [self.tableView reloadData];
}

- (id)initWithStyle:(UITableViewStyle)style
{
    self = [super initWithStyle:style];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (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;
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

#pragma mark - Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    // Return the number of sections.
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    // Return the number of rows in the section.
    return self.lists.count;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];

    // Configure the cell...
    NSManagedObject *list = [self.lists objectAtIndex:indexPath.row];
    [cell.textLabel setText:[list valueForKey:@"name"]];

    return cell;
}

-(IBAction)add:(id)sender {
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Add List" message:@"Create a New Wish List" delegate:self cancelButtonTitle:@"Cancel" otherButtonTitles:@"Save", nil];
    [alert setAlertViewStyle:UIAlertViewStylePlainTextInput];
    [alert setTag:2];
    [alert show];
    alert.delegate = self;
}
- (void) alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
{
    if (buttonIndex != 0 && alertView.tag == 2) {
        UITextField *tf = [alertView textFieldAtIndex:0];
        NSManagedObjectContext *context = [self managedObjectContext];

        // Create a new managed object
        NSManagedObject *newList = [NSEntityDescription insertNewObjectForEntityForName:@"List" inManagedObjectContext:context];
        [newList setValue:tf.text forKey:@"name"];

        NSError *error = nil;
        // Save the object to persistent store
        if (![context save:&error]) {
            NSLog(@"Can't Save! %@ %@", error, [error localizedDescription]);


        }

        [self dismissViewControllerAnimated:YES completion:nil];
    }

    NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"List"];
    self.lists = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];

    [self.tableView reloadData];

}
- (BOOL)tableView:(UITableView *)tableView canEditRowAtIndexPath:(NSIndexPath *)indexPath
{
    // Return NO if you do not want the specified item to be editable.
    return YES;
}


- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath
{
    NSManagedObjectContext *context = [self managedObjectContext];

    if (editingStyle == UITableViewCellEditingStyleDelete) {
        // Delete object from database
        [context deleteObject:[self.lists objectAtIndex:indexPath.row]];

        NSError *error = nil;
        if (![context save:&error]) {
            NSLog(@"Can't Delete! %@ %@", error, [error localizedDescription]);
            return;
        }

        // Remove list from table view
        [self.lists removeObjectAtIndex:indexPath.row];
        [self.items removeObjectAtIndex:indexPath.row];
        [self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
    }
}
@end

第二个视图的.m（显示列表中所有项目的视图）

- (NSManagedObjectContext *)managedObjectContext {
    NSManagedObjectContext *context = nil;
    id delegate = [[UIApplication sharedApplication] delegate];
    if ([delegate respondsToSelector:@selector(managedObjectContext)]) {
        context = [delegate managedObjectContext];
    }
    return context;
}

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

    // Fetch the lists from persistent data store
    NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"Item"];
    self.lists = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];
    [self.tableView reloadData];
}

- (id)initWithStyle:(UITableViewStyle)style
{
    self = [super initWithStyle:style];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (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;
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

#pragma mark - Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    // Return the number of sections.
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    // Return the number of rows in the section.
    return self.items.count;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];

    // Configure the cell...
    NSManagedObject *item = [self.items objectAtIndex:indexPath.row];
    [cell.textLabel setText:[item valueForKey:@"list"]];

    return cell;
}


- (BOOL)tableView:(UITableView *)tableView canEditRowAtIndexPath:(NSIndexPath *)indexPath
{
    // Return NO if you do not want the specified item to be editable.
    return YES;
}


- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath
{
    NSManagedObjectContext *context = [self managedObjectContext];

    if (editingStyle == UITableViewCellEditingStyleDelete) {
        // Delete object from database
        [context deleteObject:[self.items objectAtIndex:indexPath.row]];

        NSError *error = nil;
        if (![context save:&error]) {
            NSLog(@"Can't Delete! %@ %@", error, [error localizedDescription]);
            return;
        }

        // Remove device from table view
        [self.items removeObjectAtIndex:indexPath.row];
        [self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
    }
}



#pragma mark - Table view delegate

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    // Navigation logic may go here. Create and push another view controller.
    /*
     <#DetailViewController#> *detailViewController = [[<#DetailViewController#> alloc] initWithNibName:@"<#Nib name#>" bundle:nil];
     // ...
     // Pass the selected object to the new view controller.
     [self.navigationController pushViewController:detailViewController animated:YES];
     */
}


#pragma mark - Segue

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    if ([[segue identifier] isEqualToString:@"ShowDetails"]) {
        NSManagedObject *selectedItem = [self.items objectAtIndex:[[self.tableView indexPathForSelectedRow] row]];
        AddViewController *destViewController = segue.destinationViewController;
        destViewController.items = selectedItem;
    }
}

@end

最后一个视图（将项目添加到列表中的视图）

- (NSManagedObjectContext *)managedObjectContext {
    NSManagedObjectContext *context = nil;
    id delegate = [[UIApplication sharedApplication] delegate];
    if ([delegate respondsToSelector:@selector(managedObjectContext)]) {
        context = [delegate managedObjectContext];
    }
    return context;
}

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (IBAction)cancel:(id)sender {
    [self dismissViewControllerAnimated:YES completion:nil];
}

- (IBAction)save:(id)sender {
    NSManagedObjectContext *context = [self managedObjectContext];

    // Create a new managed object
    NSManagedObject *newItem = [NSEntityDescription insertNewObjectForEntityForName:@"Item" inManagedObjectContext:context];
    [newItem setValue:self.lists forKey:@"list"];
    [newItem setValue:self.lists forKey:@"list"];
    [newItem setValue:self.lists forKey:@"list"];


    NSError *error = nil;
    // Save the object to persistent store
    if (![context save:&error]) {
        NSLog(@"Can't Save! %@ %@", error, [error localizedDescription]);
    }

    [self dismissViewControllerAnimated:YES completion:nil];
}
@end

在我的模型视图中，允许我创建一个新项目：

[newItem setValue:self.name.text forKey:@"itemName"];
[newItem setValue:self.price.text forKey:@"price"];
[newItem setValue:self.desc.text forKey:@"description"];

错误：

self =（AddViewController *）0x8d22e90 newItem =（Item_Item_ *）0x8a636b0

Answer 1

我并不完全清楚所有这些控制器是如何连接在一起的。使用Core Data时需要考虑的一些建议：

有多种方法可以处理您在主队列中使用的托管对象上下文。许多人使用依赖注入来沿控制器层次结构传递上下文，而不是在每个控制器中向应用程序委托询问它。
您可以通过继承NSManagedObject来大大简化您的生活，这样您就不必使用KVC来访问实体上的属性。 Xcode可以为你做到;但是发电机提供了更多。
NSFetchedResultsController有时可以帮助简化核心数据和表格视图的使用;但它也增加了自己的一系列怪癖。

尽管如此，我无法判断这些问题是否与您的问题有关或是否有所帮助;所以我整理了一个示例应用程序，它大致反映了您尝试做的事情的一部分。（我认为...）它遗漏了很多从用户那里收集数据的逻辑，但你可以看看你如何考虑整合这样的核心数据应用程序。

请参阅github上的this repository。

核心数据未保存到表视图

1 个答案: