我目前正在尝试制作一个 iPhone 应用程序，但偶然发现了一个小问题。在使用 NSFetchedResultsControllerDelegate 和使用 NSFetchedResults 控制器的任何地方时，我都会收到错误消息。当我在我的代码中实现 Core Data 时，我必须让它工作。欢迎任何反馈。
这是代码：
ClassTableViewController.h
#import <UIKit/UIKit.h>
#import "Classes.h"
//@protocol NewClassViewControllerDelegate;
@interface NewClassViewController : UIViewController
//@property (weak, nonatomic) id <NewClassViewControllerDelegate> delegate;
@property (weak, nonatomic) IBOutlet UITextField *classTextField;
@property (weak, nonatomic) IBOutlet UITextField *periodTextField;
@property (strong, nonatomic) Classes *classID;
- (IBAction)saveClass:(id)sender;
@end
ClassTableViewController.m
#import "ClassTableViewController.h"
#import "Classes.h"
#import "ClassTableViewCell.h"
#import "NewClassViewController.h"
@interface ClassTableViewController ()
- (void)configureCell:(ClassTableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath;
@end
@implementation ClassTableViewController
- (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:@"Classes" 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)];
}
- (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;
}
- (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:@"Classes " inManagedObjectContext: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];
}
/*
// 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