我刚开始学习斯威夫特，所以这个问题的程度对你来说可能已经足够明显了，但是，我只是不明白该怎么做。
我“创建”了一个简单的应用程序，允许你添加你一天的日志。每个单元格存储您添加的时间、一个根据时间而更改的自定义图标以及日志文本本身（简单文本）。
一切正常。但是，由于我不知道“用户默认值”的内容，每当我关闭应用程序时，时钟都会重置。
我读了很多关于用户默认值的文章，但是我不知道如何保存我的数据，即使我关闭了应用程序。
我试着这样做：
class ToDoItem: NSObject, NSCoding {
var title: String
var date: String
var type: String!
public init(title: String, date: String, type: String) {
self.title = title
self.date = date
self.type = type
}
required init?(coder aDecoder: NSCoder)
{
// Try to unserialize the "title" variable
if let title = aDecoder.decodeObject(forKey: "title") as? String
{
self.title = title
let dateFormatter = DateFormatter()
dateFormatter.dateStyle = .none
dateFormatter.timeStyle = .short
self.date = dateFormatter.string(from: Date())
let hour = NSCalendar.current.component(.hour, from: Date())
var tempType = ""
switch hour {
case 5..<9: tempType = "morning_1"
case 6..<12: tempType = "morning_2"
case 12: tempType = "noon_1"
case 13..<16: tempType = "afternoon_1"
case 16..<20: tempType = "dusk_1"
case 20..<23: tempType = "evening_1"
case 23..<00: tempType = "midnight_1"
default: tempType = "morning_1"
}
self.type = tempType
}
else
{
// There were no objects encoded with the key "title",
// so that's an error.
return nil
}
let userDefaults = UserDefaults.standard
userDefaults.set(true, forKey: "title")
}
func encode(with aCoder: NSCoder)
{
// Store the objects into the coder object
aCoder.encode(self.title, forKey: "title")
let defaults = UserDefaults.standard
defaults.set(false, forKey: "title")
}
}
extension Collection where Iterator.Element == ToDoItem
{
// Builds the persistence URL. This is a location inside
// the "Application Support" directory for the App.
private static func persistencePath() -> URL?
{
let url = try? FileManager.default.url(
for: .applicationSupportDirectory,
in: .userDomainMask,
appropriateFor: nil,
create: true)
return url?.appendingPathComponent("todoitems.bin")
}
// Write the array to persistence
func writeToPersistence() throws
{
if let url = Self.persistencePath(), let array = self as? NSArray
{
let data = NSKeyedArchiver.archivedData(withRootObject: array)
try data.write(to: url)
}
else
{
throw NSError(domain: "com.example.MyToDo", code: 10, userInfo: nil)
}
}
// Read the array from persistence
static func readFromPersistence() throws -> [ToDoItem]
{
if let url = persistencePath(), let data = (try Data(contentsOf: url) as Data?)
{
if let array = NSKeyedUnarchiver.unarchiveObject(with: data) as? [ToDoItem]
{
return array
}
else
{
throw NSError(domain: "com.example.MyToDo", code: 11, userInfo: nil)
}
}
else
{
throw NSError(domain: "com.example.MyToDo", code: 12, userInfo: nil)
}
}
}
有人能帮帮我吗？或者至少指点我该怎么做？谢谢您！
最佳答案
你使用的是NSKeyedArchiver和NSKeyedUnarchiver这是一种不同于UserDefaults的机制。两者都是完全有效的，但你必须选一个，它们不能一起工作。
在这里，您将归档和取消归档ToDoItem的数组。要使其工作，ToDoItem必须是可归档的，这意味着它必须实现NSCoding协议，即：
public protocol NSCoding {
public func encode(with aCoder: NSCoder)
public init?(coder aDecoder: NSCoder) // NS_DESIGNATED_INITIALIZER
}
必须将要保存的所有属性添加到
NSCoder对象或从中提取。下面是一个例子：class ToDoItem: NSObject, NSCoding
{
var title: String
var date: Date
required init?(coder aDecoder: NSCoder)
{
guard let title = aDecoder.decodeObject(forKey: "title") as? String else {
return nil
}
guard let date = aDecoder.decodeObject(forKey: "date") as? Date else {
return nil
}
self.title = title
self.date = date
}
func encode(with aCoder: NSCoder)
{
aCoder.encode(self.title, forKey: "title")
aCoder.encode(self.date, forKey: "date")
}
}