如何使用swift将自定义结构数组保存到NSUserDefault？

Question

我有一个名为'新闻'的自定义结构,我想将其附加到NSUserDefault的数组中.但它显示错误"类型'新闻'不符合协议'AnyObject'".

我不想将'News'结构更改为类,因为它已经被用于其他代码.无论如何我可以将NSUserDefaults.standardUserDefaults().arrayForKey("savedNewsArray")类型更改为[新闻]？

var savedNews = NSUserDefaults.standardUserDefaults().arrayForKey("savedNewsArray")
var addSavedNews = savedNews as? [News]
addSavedNews.append(News(id: "00", title: newsTitle, source: source, imageURL: imageURL, url: url))
NSUserDefaults.standardUserDefaults().setObject(addSavedNews, forKey: "savedNewsArray")
NSUserDefaults.standardUserDefaults().synchronize()

这是'新闻'结构.

public struct News {
    public var id: String
    public var title: String
    public var source: String?
    public var imageURL: String?
    public var date: NSDate?
    public var url: String

    init(id: String, title: String, source: String, imageURL: String, url: String) {
        self.id = id
        self.title = title
        self.source = source
        self.imageURL = imageURL
        self.url = url
    }
}

Answer 1

NSUserDefaults的只能保存一个非常小的一组类型:NSData,NSString,NSNumber,NSDate,NSArray只包含这些类型,或NSDictionary仅含有这些类型.因此,最好的办法是使用NSKeyedUnarchiver对结构进行编码,这需要一个符合NSCoding的值.你可以让你的类型符合这一点,但我认为从你的用户隐藏它并且只是为内部表示设置一个私有类更清晰,如下所示:

struct Foo {
    var a : String
    var b : String?
}

extension Foo {
    init?(data: NSData) {
        if let coding = NSKeyedUnarchiver.unarchiveObjectWithData(data) as? Encoding {
            a = coding.a as String
            b = coding.b as String?
        } else {
            return nil
        }
    }

    func encode() -> NSData {
        return NSKeyedArchiver.archivedDataWithRootObject(Encoding(self))
    }

    private class Encoding: NSObject, NSCoding {
        let a : NSString
        let b : NSString?

        init(_ foo: Foo) {
            a = foo.a
            b = foo.b
        }

        @objc required init?(coder aDecoder: NSCoder) {
            if let a = aDecoder.decodeObjectForKey("a") as? NSString {
                self.a = a
            } else {
                return nil
            }
            b = aDecoder.decodeObjectForKey("b") as? NSString
        }

        @objc func encodeWithCoder(aCoder: NSCoder) {
            aCoder.encodeObject(a, forKey: "a")
            aCoder.encodeObject(b, forKey: "b")
        }

    }
}

然后,要保存数组,您只需映射.encode数组:

let fooArray = [ Foo(a: "a", b: "b"), Foo(a: "c", b: nil) ]
let encoded = fooArray.map { $0.encode() }
NSUserDefaults.standardUserDefaults().setObject(encoded, forKey: "my-key")

并且要将其恢复,您只需将其传递NSData给init:

let dataArray = NSUserDefaults.standardUserDefaults().objectForKey("my-key") as! [NSData]
let savedFoo = dataArray.map { Foo(data: $0)! }