swift 保存和清空用户首选项实例

import UIKit

class ViewController: UIViewController {

    let KEY_NAME = "inputData"
    
    @IBOutlet weak var inputText: UITextField!
    @IBOutlet weak var outputText: UITextField!
    
    var ud: NSUserDefaults = NSUserDefaults.standardUserDefaults()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view,typically from a nib.
    
        //初期化时取得首选项内容，并显示到output中
        if var value: AnyObject = ud.objectForKey(KEY_NAME) {
            
            //命名为“inputData”的设定项存在的话设定
            outputText.text = value as String
        } else {
            
            outputText.text = "设定项不存在"
        }
        
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }

    @IBAction func SaveText(sender: AnyObject) {
    
        //设定（保存）用户首选项
        ud.setObject(inputText.text,forKey: KEY_NAME)
    
    }

    @IBAction func ClearText(sender: AnyObject) {
    
        //移除用户设定（保存）的首选项
        ud.removeObjectForKey(KEY_NAME)
    }
}

用户首选项，是以应用为单位保存的用户的设定项目