ios - 核心数据未保存到 TableView

Question

所以这是我第一次使用核心数据，到目前为止还不是最好的体验。到目前为止，我的应用程序由两个 UITableView Controller 和一个 ViewController 组成。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中，并将列表的名称放入第一个 TableView 中。然后用户单击列表的名称并将它们推送到列表中的内容，该列表是空的，因为它尚未填充。然后用户填充 TableView，因此它会推送到单个 View Controller ，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，它返回到最后一个 UITableView Controller 并且什么都没有。这是我的第一个问题，第二个是我想在 View 之间传递数据，所以当用户单击列表时，它会推送到第二个 UITableView Controller 并在顶部说出列表的名称。我对所有核心数据的内容和关系感到非常困惑，所以如果有人能帮助我，我将不胜感激。我将包括我的代码和数据模型。

数据模型

First Views .m(列出所有列表的 View )

- (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 View 的 .m(显示列表中所有项目的 View )

- (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 View (将项目添加到列表的 View )

- (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

在允许我创建新项目的模型 View 中:

[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 *)0x8d22e90newItem=(Item_Item_ *)0x8a636b0

Answer 1

我并不完全清楚所有这些 Controller 是如何连接在一起的。使用核心数据时需要考虑的一些建议:

• 有多种方法可以处理您将在主队列上使用的托管对象上下文。许多使用依赖项注入(inject)沿着 Controller 层次结构传递上下文，而不是在每个 Controller 中向应用程序委托(delegate)请求它。

• 您可以通过子类化 NSManagedObject 来大大简化您的生活，这样您就不必使用 KVC 来访问实体的属性。 Xcode 可以为您完成；但 mogenerator 提供的更多。

• NSFetchedResultsController 有时可以帮助简化核心数据和表格 View 的使用；但它也增加了自己的一套怪癖。

也就是说，我无法判断这是否与您的问题有关或是否一定有帮助；所以我整理了一个示例应用程序，它大致反射(reflect)了您想要做的部分内容。 (我认为......)它遗漏了很多从用户等处收集数据的逻辑，但你可以看看你可能会考虑如何将这样的核心数据应用程序放在一起。

参见this repository在 github 上。