从核心数据中获取记录时返回空值

Question

朋友们，当我从核心数据中获取记录时，它显示为 null 。我不知道是什么问题。如果有人能解决我的问题，我会非常高兴。这是我的代码。

注意：我在名为“dbmanager”的单独文件中返回了所有核心数据函数

dbmanager.m

- (NSArray *)fetchAllAds {
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
[fetchRequest setEntity:[NSEntityDescription entityForName:@"Ad" 
inManagedObjectContext:dbManager.managedObjectContext]];
NSError *error = nil;
NSArray *results = [managedObjectContext executeFetchRequest:fetchRequest error:&error]; 
return results;
}

- (Ad*)addToFavourite:(NSNumber*)adId text:(NSString*)text type:(LinkupType)type {

Ad *item = (Ad*)[NSEntityDescription insertNewObjectForEntityForName:@"Ad" 
inManagedObjectContext:self.managedObjectContext]; 
item.adId = adId;
item.data =text;
item.state = [NSNumber numberWithInt:type];
[self save];
return item;  
}

- (void)save {
NSError *error = nil;
if (![[self managedObjectContext] save:&error]) {
    // Update to handle the error appropriately.
    NSLog(@"Unresolved error7 %@, %@", error, [error userInfo]);
    exit(-1);  // Fail
}
}

MYviewcontroller.m

- (void)viewDidLoad
 {
self.fetchedRecordsArray = [[DBManager instance]fetchAllAds];
[[DBManager instance]managedObjectContext];
[self.shoppingtbl reloadData];
//NSLog(@"the fetched data is %@",[[DBManager instance]fetchAllAds]);
[super viewDidLoad];
}

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{

return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
return [self.fetchedRecordsArray count];

}


- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath 
*)indexPath
{
static NSString *CellIdentifier = @"ShoppingCart";
ShoppingCart *cell = (ShoppingCart*)[tableView dequeueReusableCellWithIdentifier:CellIdentifier
                                                                    forIndexPath:indexPath];
ad=[self.fetchedRecordsArray objectAtIndex:indexPath.row];
cell.addesc.text =[NSString stringWithFormat:@"%@",ad.data];
cell.adId.text=[NSString stringWithFormat:@"%lu", (long)[ad.adId integerValue]];
cell.adstatus.text=[NSString stringWithFormat:@"%@",ad.state];
return cell;

}

请尝试解决我的问题。当我签入 nslog 时，它显示如下：

     "<Ad: 0x9751570> (entity: Ad; id: 0x974c6b0 <x-coredata://B3AA111F-8307-4A16-B898-403A804DFDFB/Ad/p56> ; data: <fault>)",
"<Ad: 0x974e370> (entity: Ad; id: 0x9751af0 <x-coredata://B3AA111F-8307-4A16-B898-403A804DFDFB/Ad/p57> ; data: <fault>)"

note:  status section is showing properly!

Answer 1

使用 NSFetchedResultsController 而不是使用单独的 fetchedRecordsArray 数组。通过代码保持 ManagedObjects 不是线程安全的。