Ios NSFetchedResultsController能否与NSDictionaryResultType一起工作？

我使用核心数据将店铺存储为

实体

店铺，并且在我拥有

属性

城市的每个店铺上，我希望按城市对店铺进行分组，并显示一个包含所有城市的

UITableView

。我使用

NSFetchedResultsController

获取数据并刷新

UITableView

，因为我想对城市进行分组，所以我将请求的

resultType

设置为

NSDictionaryResultType

。

---

但是现在，当我在我的

NSFetchedResultsController上使用
objectAtIndexPath
时，我得到的是
NSKnownkeysdictionary1
我的问题是，我能让
NSFetchedResultsController
处理
nsDictionaryResultsType
吗？在这种情况下，我应该停止使用
NSFetchedResultsController
采取其他方法
 必须为其设置NSExpressionDescription以获取适当的值。你可以这样做

- (NSFetchedResultsController *)fetchedResultsController
{
    if (!_fetchedResultsController) {
        NSExpression *cityKeypath = [NSExpression expressionForKeyPath:@"identifier"];
        NSExpressionDescription *cityDescription = [[NSExpressionDescription alloc] init];
        cityDescription.expression = cityKeypath;
        cityDescription.name = @"City";
        cityDescription.expressionResultType = NSStringAttributeType;


        NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Shop"];
        [fetchRequest setPropertiesToFetch:@[cityDescription]];
        [fetchRequest setPropertiesToGroupBy:@[@"city"]];
        [fetchRequest setResultType:NSDictionaryResultType];

        fetchRequest.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"city" ascending:YES]];
        _fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
                                                                        managedObjectContext:self.managedObjectContext
                                                                          sectionNameKeyPath:nil
                                                                                   cacheName:nil];

       _fetchedResultsController.delegate = self;
        NSError *error;

        [_fetchedResultsController performFetch:&error];
    }
    return _fetchedResultsController;
}

 {
   @"city": "Kansas"
  }
 ...

因此，需要为要获取的属性提供NSExpressionDescription。NSFetchedResultsController结果将在字典中显示如下类型：

- (NSFetchedResultsController *)fetchedResultsController
{
    if (!_fetchedResultsController) {
        NSExpression *cityKeypath = [NSExpression expressionForKeyPath:@"identifier"];
        NSExpressionDescription *cityDescription = [[NSExpressionDescription alloc] init];
        cityDescription.expression = cityKeypath;
        cityDescription.name = @"City";
        cityDescription.expressionResultType = NSStringAttributeType;


        NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Shop"];
        [fetchRequest setPropertiesToFetch:@[cityDescription]];
        [fetchRequest setPropertiesToGroupBy:@[@"city"]];
        [fetchRequest setResultType:NSDictionaryResultType];

        fetchRequest.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"city" ascending:YES]];
        _fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
                                                                        managedObjectContext:self.managedObjectContext
                                                                          sectionNameKeyPath:nil
                                                                                   cacheName:nil];

       _fetchedResultsController.delegate = self;
        NSError *error;

        [_fetchedResultsController performFetch:&error];
    }
    return _fetchedResultsController;
}

 {
   @"city": "Kansas"
  }
 ...

它似乎会起作用，但如何访问
cellforrowatinexpath
的字典？似乎
objectAtIndexPath
和
fetchedObjects
from
NSFetchedResultsController
都不能真正做到这一点。fetchedObjects应该为您提供字典数组。