如何使用NSPredicate使用今天的NSDate获取对象？

我困在我的核心数据模型和涉及date的提取请求的问题。

我有一个具有NSDate属性的实体中的一些对象; 我需要提取与今天的date对象，但我总是从这个代码无：

public func getObjectsOfToday() -> Array<myObject>? { let entityDescription = NSEntityDescription.entityForName("Objects", inManagedObjectContext: DataAccess.sharedInstance.managedObjectContext) let request = NSFetchRequest() request.entity = entityDescription request.returnsObjectsAsFaults = false let today = NSDate() request.predicate = NSPredicate(format: "(dateStart => %@) AND (dateStart <= %@)", today, today) var objects: [AnyObject]? do { objects = try DataAccess.sharedInstance.managedObjectContext.executeFetchRequest(request) } catch let error as NSError { print(error) objects = nil } return objects as? Array<Objects> } 

问题我认为这是NSPredicate，因为它也考虑到小时，分钟和秒钟。 如果我今天打印的东西是这样的：

打印今天的描述：2016-02-28 22:02:01 +0000

但是我想用相同的date获取对象，忽略小时，分钟和秒 。 我需要做什么？

我也尝试使用组件创build另一个NSDate：

 let components = cal.components([.Day , .Month, .Year ], fromDate: today) let newDate = cal.dateFromComponents(components) 

但结果是一样的。 我究竟做错了什么？

Answer 1

我所做的就是将它与今天的开始和结束进行比较，并有一些辅助function来计算它们：

 class DateHelper{ internal class func startOfDay(day: NSDate) -> NSDate { let gregorian = NSCalendar(calendarIdentifier: NSCalendarIdentifierGregorian) let unitFlags: NSCalendarUnit = [.Minute, .Hour, .Day, .Month, .Year] let todayComponents = gregorian!.components(unitFlags, fromDate: day) todayComponents.hour = 0 todayComponents.minute = 0 return (gregorian?.dateFromComponents(todayComponents))! } internal class func endOfDay(day: NSDate) -> NSDate { let gregorian = NSCalendar(calendarIdentifier: NSCalendarIdentifierGregorian) let unitFlags: NSCalendarUnit = [.Minute, .Hour, .Day, .Month, .Year] let todayComponents = gregorian!.components(unitFlags, fromDate: day) todayComponents.hour = 23 todayComponents.minute = 59 return (gregorian?.dateFromComponents(todayComponents))! } } 

所以在你的代码中，你可以调用：

 request.predicate = NSPredicate(format: "(dateStart => %@) AND (dateStart <= %@)", DateHelper.startOfDay(today), DateHelper.endOfDay(today)) 

Answer 2

创build一个开始date，获取一天的时间（间隔），添加开始date的时间间隔来获得第二天的开始。

 var startOfToday: NSDate? var interval: NSTimeInterval = 0 NSCalendar.currentCalendar().rangeOfUnit(.Day, startDate: &startOfToday, interval: &interval, forDate: NSDate()) let startOfTomorrow = startOfToday!.dateByAddingTimeInterval(interval) 

创build谓词

 let predicate = NSPredicate(format: "dateStart >= %@ AND dateStart < %@", startOfToday, startOfTomorrow) 

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我使用了以下testing代码，没有核心数据的麻烦

 import Foundation let dates:[NSDate] = { var dates:[NSDate] = [] dates.append({ let c = NSDateComponents() c.year = 2016 c.month = 2 c.day = 1 return NSCalendar.currentCalendar().dateFromComponents(c)! }()) dates.append({ let c = NSDateComponents() c.year = 2016 c.month = 2 c.day = 3 return NSCalendar.currentCalendar().dateFromComponents(c)! }()) dates.append({ let c = NSDateComponents() c.year = 2016 c.month = 3 c.day = 1 return NSCalendar.currentCalendar().dateFromComponents(c)! }()) dates.append({ let c = NSDateComponents() c.year = 2016 c.month = 2 c.day = 28 c.hour = 12 c.minute = 30 return NSCalendar.currentCalendar().dateFromComponents(c)! }()) dates.append({ let c = NSDateComponents() c.year = 2016 c.month = 2 c.day = 28 c.hour = 11 c.minute = 15 return NSCalendar.currentCalendar().dateFromComponents(c)! }()) return dates }() var startOfToday: NSDate? var interval: NSTimeInterval = 0 NSCalendar.currentCalendar().rangeOfUnit(.Day, startDate: &startOfToday, interval: &interval, forDate: NSDate()) if let startOfToday = startOfToday { let startOfTomorrow = startOfToday.dateByAddingTimeInterval(interval) let predicate = NSPredicate(format: "self >= %@ AND self < %@", startOfToday, startOfTomorrow) let filteredArray = dates.filter({predicate.evaluateWithObject($0)}) print(filteredArray) } 

结果：

 [2016-02-28 11:30:00 +0000, 2016-02-28 10:15:00 +0000]