Core data 核心数据：无法访问获取结果控制器返回的托管对象

我正在为iPad开发一个应用程序，但无法显示已经保存在核心数据中的数据。我之前问过这个问题，很多人都帮过我，但我仍然有同样的问题。这一次，在调试过程中，我得到一个错误，即我设置用来接收获取对象的数组无法访问

我的代码如下：

    #import "RootViewController.h"
    #import "DetailViewController.h"
    #import "AddViewController.h"
    #import "EmployeeDetailsAppDelegate.h"

/*
 This template does not ensure user interface consistency during editing operations in the table view. You must implement appropriate methods to provide the user experience you require.
 */

@interface RootViewController ()
- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath;
@end



@implementation RootViewController

@synthesize detailViewController, fetchedResultsController, managedObjectContext, array, dictionary;
//@synthesize array;

#pragma mark -
#pragma mark View lifecycle

- (void)viewDidLoad {

    self.title = @"Employee Name";
    self.navigationItem.rightBarButtonItem = self.editButtonItem;
    [super viewDidLoad];

    if (self.fetchedResultsController) 
    {
        NSArray *tempArr = self.fetchedResultsController.fetchedObjects;
        NSLog(@"temp array is %@",tempArr);
        int count =[tempArr count];
        int i;
        for(i=0;i <count;i++)
        {
            NSManagedObject *category = [tempArr objectAtIndex:i];
            dictionary = [[NSMutableDictionary alloc] initWithCapacity:0];

            if([[category valueForKey:@"EmployeeName"] isKindOfClass:[NSString class]])
            {
                [dictionary setObject:[category valueForKey:@"EmployeeName"] forKey:@"EmployeeName"];
            }

            if([[category valueForKey:@"EmployeeID"] isKindOfClass:[NSString class]])
            {
                [dictionary setObject:[category valueForKey:@"EmployeeID"] forKey:@"EmployeeID"];
            }
            if([[category valueForKey:@"EmployeeDepartment"] isKindOfClass:[NSString class]])
            {
                [dictionary setObject:[category valueForKey:@"EmployeeDepartment"] forKey:@"EmployeeDepartment"];
            }

            [dictionary setObject:[NSNumber numberWithInt:0] forKey:@"EmployeeName"];

        [self.array addObject:dictionary];

        [dictionary release];
        [tempArr release];
        }
    }
}




- (void)viewWillAppear:(BOOL)animated {

    [self.tableView reloadData];
//    [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 {
    // Ensure that the view controller supports rotation and that the split view can therefore show in both portrait and landscape.    
    return YES;
}

#pragma mark -
#pragma mark Add a new object

- (void)insertNewObject:(id)sender {

    AddViewController *add = [[AddViewController alloc]initWithNibName:@"AddViewController" bundle:nil];
    self.modalPresentationStyle = UIModalPresentationFormSheet;
    add.wantsFullScreenLayout = NO;

    [self presentModalViewController:add animated:YES];
    [add release];  
}   


#pragma mark -
#pragma mark Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return 1;
}


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

//  id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section];
//    return [sectionInfo numberOfObjects];
    if([self.array count])
    {
        return [array count];
    }
    return 1;
}


- (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.

//  [self configureCell:cell atIndexPath:indexPath];

    if(dictionary = [array objectAtIndex:indexPath.row])
    {
        [dictionary objectForKey:@"EmployeeName"];
        cell.textLabel.text = @"(EmployeeName = %@)";        
    }

    else {
        cell.textLabel.text = @"No Employee Name";
    }


    return cell;
}

-(void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath{

//  AddViewController *detail = [fetchedResultsController objectAtIndexPath:indexPath];
//  cell.textLabel.text = detail.empName.text;
}

- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {

    if (editingStyle == UITableViewCellEditingStyleDelete) {

        // Delete the managed object.
        NSManagedObject *objectToDelete = [self.fetchedResultsController objectAtIndexPath:indexPath];
        if (self.detailViewController.detailItem == objectToDelete) {
            self.detailViewController.detailItem = nil;
        }

        NSManagedObjectContext *context = [fetchedResultsController managedObjectContext];
        [context deleteObject:[fetchedResultsController objectAtIndexPath:indexPath]];

        NSError *error;
        if (![context save:&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. If it is not possible to recover from the error, display an alert panel that instructs the user to quit the application by pressing the Home button.
             */
            NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            abort();
        }
    }   
}


- (BOOL)tableView:(UITableView *)tableView canMoveRowAtIndexPath:(NSIndexPath *)indexPath {
    // The table view should not be re-orderable.
    return NO;
}


#pragma mark -
#pragma mark Table view delegate

- (void)tableView:(UITableView *)aTableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {

    // Set the detail item in the detail view controller.

    detailViewController = [[DetailViewController alloc]initWithStyle:UITableViewStylePlain];
//  AddViewController *selectedName = (AddViewController *)[[self fetchedResultsController]objectAtIndexPath:indexPath];
//  detailViewController.detail = selectedName;
    [self.navigationController pushViewController:detailViewController animated:YES];
    [detailViewController release];
}


#pragma mark -
#pragma mark Fetched results controller

- (NSFetchedResultsController *)fetchedResultsController {

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

    /*
     Set up the fetched results controller.
     */
    // Create the fetch request for the entity.
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    // Edit the entity name as appropriate.
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Details" inManagedObjectContext:self.managedObjectContext];
    [fetchRequest setEntity:entity];

    // Set the batch size to a suitable number.
    [fetchRequest setFetchBatchSize:20];

    // Edit the sort key as appropriate.

    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"EmployeeName" ascending:NO];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];

    AddViewController *name = [[AddViewController alloc]init];

    if (name.empName.text) {
        NSPredicate *inPredicate = [NSPredicate predicateWithFormat: @"EmployeeName = %@", name.empName.text];
        [fetchRequest setPredicate:inPredicate];
    }

    [fetchRequest setSortDescriptors:sortDescriptors];

    // Edit the section name key path and cache name if appropriate.
    // nil for section name key path means "no sections".
    NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:managedObjectContext sectionNameKeyPath:nil cacheName:@"Root"];
    aFetchedResultsController.delegate = self;
    self.fetchedResultsController = aFetchedResultsController;

    [aFetchedResultsController release];
    [fetchRequest release];
    [sortDescriptors release];

    return fetchedResultsController;
}    


#pragma mark -
#pragma mark Fetched results controller delegate

- (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];
}


#pragma mark -
#pragma mark Memory management

- (void)didReceiveMemoryWarning {
    // Releases the view if it doesn't have a superview.
    [super didReceiveMemoryWarning];

    // Relinquish ownership any cached data, images, etc. that aren't in use.
}


- (void)viewDidUnload {

    self.fetchedResultsController = nil;
    // Relinquish ownership of anything that can be recreated in viewDidLoad or on demand.
    // For example: self.myOutlet = nil;

//  self.array = nil;
}


- (void)dealloc {

//  [array release];
    [detailViewController release];
    [fetchedResultsController release];
    [managedObjectContext release];

    [super dealloc];
}

@end

#导入“RootViewController.h”
#导入“DetailViewController.h”
#导入“AddViewController.h”
#导入“EmployeeDetailsAppDelegate.h”
/*
在表视图中进行编辑操作时，此模板不能确保用户界面的一致性。您必须实施适当的方法来提供所需的用户体验。
*/
@接口RootViewController（）
-（void）configureCell:（UITableViewCell*）单元格atIndexPath:（NSIndexPath*）indexPath；
@结束
@RootViewController的实现
@综合detailViewController、fetchedResultsController、managedObjectContext、数组、字典；
//@综合阵列；
#布拉格标记-
#pragma标记视图生命周期
-（无效）viewDidLoad{
self.title=@“员工姓名”；
self.navigationItem.rightBarButtonItem=self.editButtonItem；
[超级视图下载]；
if（self.fetchedResultsController）
{
NSArray*tempArr=self.fetchedResultsController.fetchedObject；
NSLog（@“临时数组为%@”，tempArr）；
整数计数=[tempArr计数]；
int i；
对于（i=0；i我不确定，但我认为您将元素放入数组的方式失败了：

NSArray *tempArr = self.fetchedResultsController.fetchedObjects;

您可以尝试执行for循环并将每个对象添加到数组中。如下所示：

 NSMutableArray *tempArray = [[NSMutableArray alloc] init];

for(elementType *element in [self.fetchedResultsController fetchedObjects])
{
    [tempArray addObject: [element objectForKey: appropriateKey]];
}  

NSManagedObject *mo=[[fetchedResultsController fetchedObjects] objectAtIndex:index.row]];   
    cell.textLabel.text = [NSString stringWithFormat:@"(EmployeeName = %@)",[mo valueForKey:@"EmployeeName"]];

首先，不必要地创建一个字典数组，它只会复制已在“获取结果控制器”中返回的数组
fetchedObjects

您似乎希望检查托管对象属性的空值，但操作错误。此类型的检查：

if([[category valueForKey:@"EmployeeName"] isKindOfClass:[NSString class]])

…即使属性为无值，也将计算为TRUE，因为键值编码返回的值将是字符串（因为生成的访问器方法始终返回字符串）

处理空字段的最佳位置是数据模型本身。只需将属性
EmployeeName
的默认值设置为“No Employee Name”，就可以省去所有检查

其次，您对数组使用的引用不一致。有时您使用的是
self.array
，而其他时候仅使用
array
。只有在使用第一种形式时，您才能获得适当的保留。如果使用第二种形式，您的数组可能会随机消失

第三，在
tableView:（UITableView*）tableView cell for rowatinexpath:
此行：

if(dictionary = [array objectAtIndex:indexPath.row])

…使用了错误的访问表单，因此它可能会或可能不会找到数组对象。此行：

cell.textLabel.text = @"(EmployeeName = %@)";

…将所有单元格的文本设置为“（EmployeeName=）”，可能会产生编译错误。它应该是：

    cell.textLabel.text = [NSString stringWithFormat:@"(EmployeeName = %@)",[dictionary objectForKey:@"EmployeeName"]];

您真的应该像这样使用“获取结果”控制器和默认字段（如上所述）：

 NSMutableArray *tempArray = [[NSMutableArray alloc] init];

for(elementType *element in [self.fetchedResultsController fetchedObjects])
{
    [tempArray addObject: [element objectForKey: appropriateKey]];
}  

NSManagedObject *mo=[[fetchedResultsController fetchedObjects] objectAtIndex:index.row]];   
    cell.textLabel.text = [NSString stringWithFormat:@"(EmployeeName = %@)",[mo valueForKey:@"EmployeeName"]];

您不必执行错误检查，因为表中的行数始终与获取的托管对象数匹配

我认为这比必要的要复杂得多。您可能已经习惯了对SQL返回的数据进行大量完整性检查。但是，核心数据和获取的结果控制器将为您处理大部分工作。在这样一个简单的设置中，您通常只需向tableview控件添加大约十行代码特罗勒模板