将字典保存到 NSUserDefaults [英] Saving dictionary into NSUserDefaults
问题描述
class AddElementVC: UIViewController {
// textfields and some other functions are defined here
@IBAction func addElement(sender: UIBarButtonItem) {
let newElement = Element(/* properties are defined here */)
var theDict = NSUserDefaults.standardUserDefaults().dictionaryForKey(tableViewData) as [String: [Element]]
if var theArray = theDict[newElement.someProperty] {
theArray += newElement
theDict[newElement.someProperty] = elementArray
} else{
theDict[newElement.someProperty] = [newElement]
}
NSUserDefaults.standardUserDefaults().setObject(theDict, forKey: tableViewData)
}
}
对上述代码的解释:
我的 tableView-app 从 [String: [Element]] 类型的字典(Element 是一个自定义类)接收数据,该字典是从 userDefaults 加载的.在第二个 viewController 中,您可以填写一些 textFields,最后按下 UIBarButtonItem.根据 textFields 的数据,创建了类Element"的新实例,并将其添加到theDict"中newElement"属性之一的键处.当我使用控制台输出检查它时,一切正常,但我最终无法将编辑过的字典保存在 userDefaults 中.没有语法错误,但是当我使用该应用程序并尝试通过第二个 viewController 将另一个元素添加到 Dictionary 时,会显示以下错误:
My tableView-app receives its data from a dictionary of type [String: [Element]] (Element is a custom class), which is loaded from the userDefaults. In a second viewController you can fill out some textFields and finally press a UIBarButtonItem. From the textFields' data a new instance of the class "Element" is created and added to "theDict" at the key of one of the "newElement"'s properties. All that works fine as I checked it with console-outputs, but I am not able to finally save the edited dictionary in the userDefaults. There are no syntax-errors, but when I use the app and try to to add another element to the Dictionary via the second viewController, the following error is displayed:
错误消息:
NSForwarding: 警告: '_TtC12myApp7Element' 类的对象 0xdcb002c 没有实现 methodSignatureForSelector: -- 麻烦提前
NSForwarding: warning: object 0xdcb002c of class '_TtC12myApp7Element' does not implement methodSignatureForSelector: -- trouble ahead
研究并没有帮助我理解错误信息.
Researches didn't help me to understand the error-message.
编辑
import Foundation
class Element: NSCoding {
enum State: String {
case state1 = "state1"
case state2 = "state2"
}
let state: State
// some more properties
init(state: String /* something more */ ){
self.state = State.fromRaw(state)!
// something more
}
init(coder aDecoder: NSCoder!) {
self.state = aDecoder.decodeObjectForKey("state") // displays error: 'AnyObject' is not convertible to 'Element.State'
// something more
}
func encodeWithCoder(aCoder: NSCoder!) {
aCoder.encodeObject(self.state, forKey: "state") // displays error: Extra Argument 'forKey' in call
// something more
}
}
推荐答案
value 参数只能是属性列表对象:NSData,NSString、NSNumber、NSDate、NSArray 或 NSDictionary.对于 NSArray 和NSDictionary 对象,它们的内容必须是属性列表对象.参见 什么是属性列表?"//apple_ref/doc/uid/10000048i" rel="noreferrer">属性列表编程指南.
The value parameter can be only property list objects: NSData, NSString, NSNumber, NSDate, NSArray, or NSDictionary. For NSArray and NSDictionary objects, their contents must be property list objects. See "What is a Property List?" in Property List Programming Guide.
您不能在字典中存储包含 Element
元素的字典.
You cannot store a dictionary with elements of Element
in the dictionary.
一种选择是确保 Element
实现 NSCoding 协议 然后使用 NSKeyedArchiver 将您的字典转换为 NSData:
One option is to make sure Element
implements the NSCoding protocol and then use NSKeyedArchiver to convert your dictionary into NSData:
// Storing the dictionary
var data = NSKeyedArchiver.archivedDataWithRootObject(theDict)
NSUserDefaults.standardUserDefaults().setObject(data, forKey: tableViewData)
// Retrieving the dictionary
var outData = NSUserDefaults.standardUserDefaults().dataForKey(tableViewData)
var dict = NSKeyedUnarchiver.unarchiveObjectWithData(outData)
您的协议实现看起来像这样:
Your protocol implementation would look like something like this:
init(coder aDecoder: NSCoder!) {
self.state = State.fromRaw(aDecoder.decodeObjectForKey("state") as String)
}
func encodeWithCoder(aCoder: NSCoder!) {
aCoder.encodeObject(self.state.toRaw(), forKey: "state")
}
您不能存储枚举,但可以存储它的原始表示形式,即字符串.
You cannot store an Enum, but you can store the raw representation of it which is a string.
这篇关于将字典保存到 NSUserDefaults的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!