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我正在尝试从我的表格视图控制器中删除一个核心数据条目，以便当我向左滑动时，会出现一个删除按钮并删除该条目。不幸的是，我收到错误消息：在第 251 和 260 行（代码发布在下面）上的类型“ClassTableViewController *”上找不到属性“类”，并且不知道该怎么做。我有一个名为 Classes.m 和 Classes 的 NSMutableObject 类.h，并且它们已被导入，但 Xcode 似乎无法识别它。

这是代码：

ClassTableViewController.m

#import "ClassTableViewController.h"
#import "Classes.m"
#import "Classes.h"
#import "ClassTableViewCell.h"
#import "NewClassViewController.h"
#import <CoreData/CoreData.h>

@interface ClassTableViewController ()
- (void)configureCell:(ClassTableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath;
@end

@implementation ClassTableViewController

@synthesize fetchedResultsController = _fetchedResultsController;
@synthesize managedObjectContext = _managedObjectContext;
@synthesize managedObjectModel = _managedObjectModel;


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

#pragma mark - Segue

- (void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    if ( [[segue identifier] isEqualToString:@"ShowClass"] ){
        NewClassViewController *dvc = (NewClassViewController *)[segue destinationViewController];
        NSIndexPath *indexPath = [self.tableView indexPathForSelectedRow];
        Classes *classID = [[self fetchedResultsController] objectAtIndexPath:indexPath];
        [dvc setClassID:classID];

    } else if  ([[segue identifier] isEqualToString:@"addClass"]) {
        NewClassViewController *dvc = (NewClassViewController *)[[segue destinationViewController] topViewController];
        [dvc setClassID:[NSEntityDescription insertNewObjectForEntityForName:@"MyClassesID" inManagedObjectContext:self.managedObjectContext]];
    }

}

#pragma mark - View lifecycle

- (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;

    self.navigationItem.leftBarButtonItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemDone target:self action:@selector(firstDone)];

    if (_managedObjectContext == nil)
    {
        _managedObjectContext = [(ClassTableViewController *)[[UIApplication sharedApplication] delegate] managedObjectContext];
        NSLog(@"After managedObjectContext: %@",  _managedObjectContext);
    }


}

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

- (void) firstDone {

    [self.navigationController  dismissModalViewControllerAnimated:YES];
}


- (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 [[self.fetchedResultsController sections] count];
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{

    id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section];

    return [sectionInfo numberOfObjects];
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{

    static NSString *CellIdentifier = @"ClassesCell";

    ClassTableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

    if (cell == nil) {
        cell = [[ClassTableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
    }

    [self configureCell:cell atIndexPath:indexPath];

    return cell;
}

#pragma mark - Table view delegate


- (void)configureCell:(ClassTableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath {
    Classes *classID = [self.fetchedResultsController objectAtIndexPath:indexPath];
    cell.classLabel.text = classID.classTitle;
    cell.periodLabel.text = classID.period;
}



#pragma mark - Fetched results controller

- (NSFetchedResultsController *)fetchedResultsController
{
    if (_fetchedResultsController != nil) {
        return _fetchedResultsController;
    }

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"MyClassesID" inManagedObjectContext:self.managedObjectContext];
    assert(self.managedObjectContext);

    [fetchRequest setEntity:entity];

    [fetchRequest setFetchBatchSize:20];

    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"period" ascending:YES];
    NSArray *sortDescriptors = [NSArray arrayWithObjects:sortDescriptor, nil];
   [fetchRequest setSortDescriptors:sortDescriptors];

    NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:@"Master"];
    aFetchedResultsController.delegate = self;
    self.fetchedResultsController = aFetchedResultsController;

    NSError *error = nil;

    if (![self.fetchedResultsController performFetch:&error]) {
        /*
         Replace this implementation with code to handle the error appropriately.

         abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
         */
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }

    return _fetchedResultsController;


}

- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
    [self.tableView beginUpdates];
}


- (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo
           atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type {

    switch(type) {
        case NSFetchedResultsChangeInsert:
            [self.tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex]
                          withRowAnimation:UITableViewRowAnimationFade];
            break;

        case NSFetchedResultsChangeDelete:
            [self.tableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex]
                          withRowAnimation:UITableViewRowAnimationFade];
            break;
    }
}


- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject
       atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type
      newIndexPath:(NSIndexPath *)newIndexPath {

    UITableView *tableView = self.tableView;

    switch(type) {

        case NSFetchedResultsChangeInsert:
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath]
                             withRowAnimation:UITableViewRowAnimationFade];
            break;

        case NSFetchedResultsChangeDelete:
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath]
                             withRowAnimation:UITableViewRowAnimationFade];
            break;

        case NSFetchedResultsChangeUpdate:
            [self configureCell:[tableView cellForRowAtIndexPath:indexPath]
                    atIndexPath:indexPath];
            break;

        case NSFetchedResultsChangeMove:
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath]
                             withRowAnimation:UITableViewRowAnimationFade];
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath]
                             withRowAnimation:UITableViewRowAnimationFade];
            break;
    }
}


- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
    [self.tableView endUpdates];
}

- (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.Classes objectAtIndex:indexPath.row]];

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

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

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

/*
// Override to support editing the table view.
- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath
{
    if (editingStyle == UITableViewCellEditingStyleDelete) {
        // Delete the row from the data source
        [tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationFade];
    }   
    else if (editingStyle == UITableViewCellEditingStyleInsert) {
        // Create a new instance of the appropriate class, insert it into the array, and add a new row to the table view
    }   
}
*/

/*
// Override to support rearranging the table view.
- (void)tableView:(UITableView *)tableView moveRowAtIndexPath:(NSIndexPath *)fromIndexPath toIndexPath:(NSIndexPath *)toIndexPath
{
}
*/

/*
// Override to support conditional rearranging of the table view.
- (BOOL)tableView:(UITableView *)tableView canMoveRowAtIndexPath:(NSIndexPath *)indexPath
{
    // Return NO if you do not want the item to be re-orderable.
    return YES;
}
*/

/*
#pragma mark - Navigation

// In a story board-based application, you will often want to do a little preparation before navigation
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    // Get the new view controller using [segue destinationViewController].
    // Pass the selected object to the new view controller.
}

 */

@end

我收到错误的代码：

第 251 行：

    [context deleteObject:[self.Classes objectAtIndex:indexPath.row]];

第 260 行：

    [self.Classes removeObjectAtIndex:indexPath.row];
4

2 回答 2

3

首先，删除#import "Classes.m"。其次，我假设 self.Classes 是一个数组，这引发了两个问题：

  1. 如果你的类被命名Classes，那么为什么你的变量Classes也被命名？将变量重命名为vClassesoraClasses或classes。另外，请确保self.classes（或在您的情况下self.Classes）正确初始化。调试！
  2. Classes设置好后，为什么要为对象使用数组NSFetchedResultsController？你应该self.fetchedResultsController改用。

希望能帮助到你。

于 2013-08-13T05:07:08.467 回答
0

错误很明显，这个类中没有名为“Classes”的属性，请确保您导入了名为 Classes 的类，但它不是属性/实例变量。至少我看到的不是……

[self.Classes removeObjectAtIndex:indexPath.row];

这行没有意义，你应该告诉你的数据源删除对象......

于 2013-08-13T05:13:12.897 回答