Question

我有一个获取请求，该请求可以产生一个包含结果中两个部分的tableview。

我的模特：

@interface Player : NSManagedObject

@property (nonatomic, retain) NSString * name;
@property (nonatomic, retain) NSNumber * isFacebookFriend;

此模型上的获取请求应该会生成一个部分，其中一个部分中的isFacebookFriend == YES，而第二部分中的isFacebookFriend == NO。

我试过

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
HBAppDelegate *appDelegate = [UIApplication sharedApplication].delegate;
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Player" inManagedObjectContext:appDelegate.managedObjectContext];
[fetchRequest setEntity:entity];
NSSortDescriptor *nameDescriptor = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:NO];
[fetchRequest setSortDescriptors:@[nameDescriptor]];
[fetchRequest setResultType:NSDictionaryResultType];
[fetchRequest setPropertiesToGroupBy:@[@"isFacebookFriend"]];
_fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:appDelegate.managedObjectContext sectionNameKeyPath:nil cacheName:@"playerCache"];
NSError *error;
[_fetchedResultsController performFetch:&error];

但那没有做到。错误是：

2013-06-12 12:27:28.364 TwentyQuestions[25015:c07] Unbalanced calls to begin/end appearance transitions for <UINavigationController: 0xb676aa0>.
2013-06-12 12:27:31.119 TwentyQuestions[25015:c07] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'SELECT clauses in queries with GROUP BY components can only contain properties named in the GROUP BY or aggregate functions ((<NSAttributeDescription: 0xc382320>), name hasRegisteredForGame, isOptional 1, isTransient 0, entity Player, renamingIdentifier hasRegisteredForGame, validation predicates (
), warnings (
), versionHashModifier (null)
 userInfo {
}, attributeType 800 , attributeValueClassName NSNumber, defaultValue (null) is not in the GROUP BY)'

Answer 1

要创建包含节的表视图，您必须使用sectionNameKeyPath参数 NSFetchedResultsController。您还必须添加一个（第一个）排序描述符根据部分名称键路径。

NSSortDescriptor *nameDescriptor = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:NO];
NSSortDescriptor *isFacebookFriendDescriptor = [[NSSortDescriptor alloc] initWithKey:@"isFacebookFriend" ascending:NO];
[fetchRequest setSortDescriptors:@[isFacebookFriendDescriptor, nameDescriptor]];
_fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
            managedObjectContext:appDelegate.managedObjectContext
              sectionNameKeyPath:@"isFacebookFriend"
                       cacheName:@"playerCache"];

您不必设置setPropertiesToGroupBy，我也不建议您设置 NSDictionaryResultType因为这会禁用自动更新通知。

具有分组的核心数据NSFetchRequest

1 个答案: