如何使我在UIAlertController内的UITextField中输入的数据通过Swift中的重置保持不变？

我一直在尝试在浏览器应用程序中集成Pinboard书签视图（通过解析RSS Feed并将其显示在TableView中）。为了获取提要的用户名和API令牌，我在应用程序的“设置”视图中有一个UIAlertController。输入的详细信息将在整个会话中保留，但是如果我从多任务视图中强制退出该应用程序，则这些详细信息将被删除。我怎样才能让他们留下来？

这是我用于UIAlertController的代码：

@IBAction func pinboardUserDetailsRequestAlert(sender: AnyObject) {
    //Create the AlertController
    var pinboardUsernameField :UITextField?
    var pinboardAPITokenField :UITextField?
    let pinboardUserDetailsSheetController: UIAlertController = UIAlertController(title: "Pinboard Details", message: "Please enter your Pinboard Username and API Token to access your bookmarks", preferredStyle: .Alert)
    //Add a text field
    pinboardUserDetailsSheetController.addTextFieldWithConfigurationHandler({(usernameField: UITextField!) in
        usernameField.placeholder = "Username"
        var parent = self.presentingViewController as! ViewController
        usernameField.text = parent.pinboardUsername
        pinboardUsernameField = usernameField
    })
    pinboardUserDetailsSheetController.addTextFieldWithConfigurationHandler({(apiTokenField: UITextField!) in
        apiTokenField.placeholder = "API Token"
        var parent = self.presentingViewController as! ViewController
        apiTokenField.text = parent.pinboardAPIToken
        pinboardAPITokenField = apiTokenField
    })
    pinboardUserDetailsSheetController.addAction(UIAlertAction(title: "Cancel", style: .Cancel, handler: nil))
    pinboardUserDetailsSheetController.addAction(UIAlertAction(title: "Done", style: .Default, handler: { (action) -> Void in
        // Now do whatever you want with inputTextField (remember to unwrap the optional)
        var parent = self.presentingViewController as! ViewController
        parent.pinboardAPIToken = pinboardAPITokenField?.text
        parent.pinboardUsername = pinboardUsernameField?.text
    }))
    //Present the AlertController
    self.presentViewController(pinboardUserDetailsSheetController, animated: true, completion: nil)

}