Swift从ManagedObjectContext获取日期数组FetchRequest

Question

我想在Core Data（保存日期数组）中为日期属性制作一个NSDates数组。所以我可以在日历中显示有天保存项目的日子。我曾尝试与下面的代码，但得到一个错误：

终止应用程序由于未捕获的异常“NSInvalidArgumentException”，理由是：“无法解析格式字符串‘savedTime’

func datesWithSavedData() -> [NSDate] { 
    let fetchRequest = NSFetchRequest(entityName: "UserData") 
    fetchRequest.predicate = NSPredicate(format: "savedTime'") 
    fetchRequest.sortDescriptors = [NSSortDescriptor(key: "savedTime", ascending: false)] 
    do { 
    let results = 
     try managedObjectContext.executeFetchRequest(fetchRequest) as? [NSDate] 
    selectedDates = results! 
    print(selectedDates) 
    } catch let error as NSError { 
    print("Could not fetch \(error), \(error.userInfo)") 
    } 

    return selectedDates as! [NSDate] 
} 

Answer 1

一种解决方法是告诉核心数据返回字典数组而不是[NSManagedObject]例如

func datesWithSavedData() -> [NSDate] { 
    let fetchRequest = NSFetchRequest(entityName: "UserData") 
    fetchRequest.sortDescriptors = [NSSortDescriptor(key: "savedTime", ascending: false)] 
    fetchRequest.resultType = .DictionaryResultType 
    fetchRequest.propertiesToFetch = ["savedTime"] 
    do { 
    let results = try managedObjectContext.executeFetchRequest(fetchRequest) as! [[String:NSDate]] 
    return results.map { $0["savedTime"] as! NSDate } 

    } catch let error as NSError { 
    print(error) 
    return [NSDate]() 
    } 
}