swift 使用UserDefaults保存数据

Posted 2021-05-19

# 1. With custom objects

Actually, you will need to archive the custom object into NSData then save it to user defaults and retrieve it from user defaults and unarchive it again. You can archive it like this
```
let teams = [Team(id: 1, name: "team1", shortname: "t1"), Team(id: 2, name: "team2", shortname: "t2")]

var userDefaults = UserDefaults.standard
let encodedData: Data = NSKeyedArchiver.archivedData(withRootObject: teams)
userDefaults.set(encodedData, forKey: "teams")
userDefaults.synchronize()
```

and unarchive it like this
```
let decoded  = userDefaults.object(forKey: "teams") as! Data
let decodedTeams = NSKeyedUnarchiver.unarchiveObject(with: decoded) as! [Team]
```

But if you just did that you will get
`.Team encodeWithCoder:]: unrecognized selector sent to instance`

You will have to make Team conform to NSCoding just like this
```
class Team: NSObject, NSCoding {
    var id: Int
    var name: String
    var shortname: String


    init(id: Int, name: String, shortname: String) {
        self.id = id
        self.name = name
        self.shortname = shortname

    }

    required convenience init(coder aDecoder: NSCoder) {
        let id = aDecoder.decodeInteger(forKey: "id")
        let name = aDecoder.decodeObject(forKey: "name") as! String
        let shortname = aDecoder.decodeObject(forKey: "shortname") as! String
        self.init(id: id, name: name, shortname: shortname)
    }

    func encode(with aCoder: NSCoder) {
        aCoder.encode(id, forKey: "id")
        aCoder.encode(name, forKey: "name")
        aCoder.encode(shortname, forKey: "shortname")
    }
}
```

*@see: http://stackoverflow.com/questions/29986957/save-custom-objects-into-nsuserdefaults*

let myVar = "myValue"
let userDefaults = UserDefaults.standard

// Saving
userDefaults.set(myVar, forKey: "myVar")
userDefaults.synchronize()

// Retriving
if let myVar = userDefaults.value(forKey: "myVar") {
        //do something here when myVar exists
    } else {
        //myVar not exists
}