Swift 2：AnyObject？ 不能转换为NSString

Question

我正在尝试使用会话检查现有登录但我被抛出此错误

“AnyObject？ 不能转换为'NSString'; 你的意思是用'as！' 迫使低垂？

在这行代码

self.usernameLabel.text = prefs.valueForKey("USERNAME") as NSString

完整的代码块是这样的

import UIKit

class ViewController: UIViewController {

@IBOutlet weak var usernameLabel: UILabel!

//Check for existing login, else show login
override func viewDidAppear(animated: Bool) {
    super.viewDidAppear(true)

    let prefs: NSUserDefaults = NSUserDefaults.standardUserDefaults()
    let isLoggedIn:Int = prefs.integerForKey("ISLOGGEDIN") as Int
    if (isLoggedIn != 1) {
        self.performSegueWithIdentifier("goToLogin", sender: self)
    } else {
        self.usernameLabel.text = prefs.valueForKey("USERNAME") as NSString
    }
}

override func viewDidLoad() {
    super.viewDidLoad()

}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}


}

修复它的最佳方法是什么？

Answer 1

尝试这个 ...

  if let username = prefs.valueForKey("USERNAME") as? String{
      self.usernameLabel.text = username
  }

或者如果你想使用NSString ..（只是一个选项）

 if let username = prefs.valueForKey("USERNAME") as? NSString{
      self.usernameLabel.text = username
  }

Answer 2

将NSString更改为String，

self.usernameLabel.text = prefs.valueForKey("USERNAME") as? String

它的工作正常，希望它有所帮助