我是新的核心数据,我试图找出如何在我的NSFetchedResultsController中创建一个自定义的sectionNameKeyPath.我有一个名为acctPeriod的属性的托管对象.这是一个NSString.我想根据该字段的前4个字符创建节.前4个字符代表会计期间的年份,不需要保存.
我已经通过这个网站,看过关于瞬态属性的帖子,但我似乎不能让他们上班.基本上我想要这个,然后为我的sectionNameKeyPath分配periodYear.
@dynamic periodYear;
-(NSString *)periodYear
{
return [self.acctPeriod substringToIndex:4];
}
任何帮助将不胜感激.
**更新：
使用马丁R.答案,我能够让它按预期工作.
- (NSFetchedResultsController *)fetchedResultsController
{
if (_fetchedResultsController != nil) {
return _fetchedResultsController;
}
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
// Edit the entity name as appropriate.
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Billing" 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:@"acctPeriod" ascending:NO];
NSArray *sortDescriptors = @[sortDescriptor];
//Predicate
NSPredicate *pred = [NSPredicate predicateWithFormat:@"clients = %@",self.client];
NSLog(@"%@",pred);
//[fetchRequest setResultType:NSDictionaryResultType];
//[fetchRequest setReturnsDistinctResults:YES];
[fetchRequest setPredicate:pred];
[fetchRequest setSortDescriptors:sortDescriptors];
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:@"periodYear" cacheName:nil];
aFetchedResultsController.delegate = self;
self.fetchedResultsController = aFetchedResultsController;
NSError *error = nil;
if (![self.fetchedResultsController performFetch:&error])
{
NSLog(@"Unresolved error %@,%@",error,[error userInfo]);
abort();
}
return _fetchedResultsController;
}
解决方法
以下内容应该运行：实现PeriodYear方法(将使用它)
作为“分区名称键路径”)在您的托管对象子类的类扩展中：
作为“分区名称键路径”)在您的托管对象子类的类扩展中：
@interface Event (AdditionalMethods)
- (NSString *)periodYear;
@end
@implementation Event (AdditionalMethods)
- (NSString *)periodYear {
return [self.acctPeriod substringToIndex:4];
}
@end
确保acctPeriod被用作提取请求的第一个(或唯一)排序描述符：
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"acctPeriod" ascending:YES]; NSArray *sortDescriptors = @[sortDescriptor]; [fetchRequest setSortDescriptors:sortDescriptors];
对于获取的结果控制器,使用periodYear作为sectionNameKeyPath：
NSFetchedResultsController *_fetchedResultsController = [[NSFetchedResultsController alloc]
initWithFetchRequest:fetchRequest
managedObjectContext:self.managedObjectContext
sectionNameKeyPath:@"periodYear"
cacheName:nil];
_fetchedResultsController.delegate = self;
self.fetchedResultsController = _fetchedResultsController;
最后添加默认的titleForHeaderInSection方法：
- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section {
id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section];
return [sectionInfo name];
}
或者,您可以将periodYear定义为受管对象的临时属性.
在这种情况下,它也不会存储在数据库中,但可以以按需和缓存计算值的方式实现.
Apple开发人员库中的DateSectionTitles示例项目演示了如何工作.
