我的 iOS fetchrequest 的奇怪行为有两个部分

Question

在我的带有 2 个部分 的 tableviewcontroller 中，构建工作正常，但应用程序崩溃。当我打开详细视图控制器以将项目添加到数据存储时，一开始崩溃，因此一个部分将有一个项目，而另一个部分将具有零项目（因为生成这些部分的两个不同谓词）。

如果我只设置一个部分，构建应用程序，存储两个不同的项目，每个部分一个，一切都很好，每个部分的项目数量相同。当我再次设置两个部分时，重新构建应用程序，运行并创建一个新项目，这些部分的编号不同：代码将保存项目，返回 tableview 将使应用程序崩溃。这是为什么呢？

#import "hommedicineTableViewController.h"
#import "cella2.h"

@interface hommedicineTableViewController ()

@end

@implementation hommedicineTableViewController
@synthesize section2Items = _section2Items;
static NSString *CellIdentifier = @"cell3";

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

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor colorWithRed:(220/255.f) green:(237/255.f) blue:(231/255.f) alpha:1.0];
    self.tableView.separatorStyle = UITableViewCellSeparatorStyleNone;
    [self.tableView registerNib:[UINib nibWithNibName:NSStringFromClass([cella2 class]) bundle:nil] forCellReuseIdentifier:NSStringFromClass([cella2 class])];
    [self.tableView registerNib:[UINib nibWithNibName:NSStringFromClass([cella2 class]) bundle:nil] forCellReuseIdentifier:CellIdentifier];
}

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
    NSPredicate *predicate1 = [NSPredicate predicateWithFormat:@"archivio like%@", @"in*"];
    NSPredicate *predicate2 = [NSPredicate predicateWithFormat:@"archivio like%@", @"ar*"];
    NSFetchRequest *fetchRequest1 = [[NSFetchRequest alloc] initWithEntityName:@"Medicine"];
    NSFetchRequest *fetchRequest2 = [[NSFetchRequest alloc] initWithEntityName:@"Medicine"];
    NSSortDescriptor *sortDescriptor1 = [[NSSortDescriptor alloc] initWithKey:@"archivio" ascending:NO];
    NSSortDescriptor *sortDescriptor2 = [[NSSortDescriptor alloc] initWithKey:@"scadenza" ascending:YES];
    [fetchRequest1 setSortDescriptors:[NSArray arrayWithObjects: sortDescriptor1, sortDescriptor2, nil]];
    NSSortDescriptor *sortDescriptor3 = [[NSSortDescriptor alloc] initWithKey:@"archivio" ascending:YES];
    [fetchRequest2 setSortDescriptors:[NSArray arrayWithObjects: sortDescriptor3, sortDescriptor2, nil]];
    [fetchRequest1 setPredicate:predicate1];
    [fetchRequest2 setPredicate:predicate2];
    self.contactarray = [[managedObjectContext executeFetchRequest:fetchRequest1 error:nil] mutableCopy];
    _section2Items = [[managedObjectContext executeFetchRequest:fetchRequest2 error:nil] mutableCopy];
    [self.tableView reloadData];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
}

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return 2;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    if (section == 0) {
            return [self.contactarray count];
    } else if (section == 1) {
            return [_section2Items count];
    } else {
    return 0;
    }
}

- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath {
    cella2 *tcell = (cella2 *)cell;
    NSManagedObject *device1 = [self.contactarray objectAtIndex:indexPath.row];
    NSManagedObject *device2 = [_section2Items objectAtIndex:indexPath.row];
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"dd-MM-YYYY"];
    NSString *dateString = [dateFormatter stringFromDate:[device1 valueForKey:@"scadenza"]];
    if (indexPath.section == 0) {
                                tcell.immagine1.image = [[UIImage alloc] initWithData:[device1 valueForKey:@"picture"]];
                                tcell.label1.text = [NSString stringWithFormat:@"%@", [device1 valueForKey:@"nominativo"]];
                                tcell.label2.text = [NSString stringWithFormat:@"Scadenza: %@", dateString];
                                tcell.label3.text = [NSString stringWithFormat:@"%@", [device1 valueForKey:@"archivio"]];
    } else {
                                tcell.label2.textColor = [UIColor colorWithRed:0.0f/255.0f green:0.0f/255.0f blue:0.0f/255.0f alpha:1.0f];
                                tcell.immagine1.image = [[UIImage alloc] initWithData:[device2 valueForKey:@"picture"]];
                                tcell.label1.text = [NSString stringWithFormat:@"%@", [device2 valueForKey:@"nominativo"]];
                                tcell.label2.text = [NSString stringWithFormat:@"Scadenza: %@", dateString];
                                tcell.label3.text = [NSString stringWithFormat:@"%@", [device2 valueForKey:@"archivio"]];
    }
}

- (UITableViewCell *)tableView:(UITableView *)tableView
         cellForRowAtIndexPath:(NSIndexPath *)indexPath {
        cella2 *cell = (cella2 *)[tableView dequeueReusableCellWithIdentifier:CellIdentifier];
        [self configureCell:cell atIndexPath:indexPath];
        return cell;
}

- (BOOL)tableView:(UITableView *)tableView canEditRowAtIndexPath:(NSIndexPath *)indexPath {
    return YES;
}

- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {
    NSManagedObjectContext *context = [self managedObjectContext];
    if (editingStyle == UITableViewCellEditingStyleDelete) {
        [context deleteObject:[self.contactarray objectAtIndex:indexPath.row]];
        NSError *error = nil;
        if (![context save:&error]) {
            NSLog(@"Can't Delete! %@ %@", error, [error localizedDescription]);
            return;
        }
        [self.contactarray removeObjectAtIndex:indexPath.row];
        [self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
    }
}

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    [self performSegueWithIdentifier:@"seg2" sender:self];
}

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    if ([[segue identifier] isEqualToString:@"seg2"]) {
        NSManagedObject *selectedDevice = [self.contactarray objectAtIndex:[[self.tableView indexPathForSelectedRow] row]];
        DettaglioViewController *destViewController = segue.destinationViewController;
        destViewController.contactdb = selectedDevice;
    }
}

 @end

Answer 1

我怀疑问题出在你的configureCell:atIndexPath: 方法上，特别是这两行：

NSManagedObject *device1 = [self.contactarray objectAtIndex:indexPath.row];
NSManagedObject *device2 = [_section2Items objectAtIndex:indexPath.row];

如果一个部分的项目多于另一部分，则其中一行将尝试越界访问数组索引（即 indexPath.row 将大于或等于数组计数）。只需将这些行移到 if/else 的相关子句中即可：

if (indexPath.section == 0) {
    NSManagedObject *device1 = [self.contactarray objectAtIndex:indexPath.row];
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"dd-MM-YYYY"];
    NSString *dateString = [dateFormatter stringFromDate:[device1 valueForKey:@"scadenza"]];
    tcell.immagine1.image = [[UIImage alloc] initWithData:[device1 valueForKey:@"picture"]];
    tcell.label1.text = [NSString stringWithFormat:@"%@", [device1 valueForKey:@"nominativo"]];
    tcell.label2.text = [NSString stringWithFormat:@"Scadenza: %@", dateString];
    tcell.label3.text = [NSString stringWithFormat:@"%@", [device1 valueForKey:@"archivio"]];
} else {
    NSManagedObject *device2 = [_section2Items objectAtIndex:indexPath.row];
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"dd-MM-YYYY"];
    NSString *dateString = [dateFormatter stringFromDate:[device2 valueForKey:@"scadenza"]];
    tcell.label2.textColor = [UIColor colorWithRed:0.0f/255.0f green:0.0f/255.0f blue:0.0f/255.0f alpha:1.0f];
    tcell.immagine1.image = [[UIImage alloc] initWithData:[device2 valueForKey:@"picture"]];
    tcell.label1.text = [NSString stringWithFormat:@"%@", [device2 valueForKey:@"nominativo"]];
    tcell.label2.text = [NSString stringWithFormat:@"Scadenza: %@", dateString];
    tcell.label3.text = [NSString stringWithFormat:@"%@", [device2 valueForKey:@"archivio"]];
}

有更简洁的编码方式，但我希望你能明白。