Question

在重新访问一些似乎与Xcode6 beta 5一起使用的代码时，我注意到我得到了“无法转换表达式的类型'[AnyObject]？”输入'NSArray'“此行的错误：

let textFields:NSArray = loginAlert.textFields as NSArray

以下是似乎是问题的代码部分：

override func viewDidAppear(animated: Bool) {
    if PFUser.currentUser() == nil{
        var loginAlert:UIAlertController = UIAlertController(title: "Sign Up / Login", message: "Please sign up or login", preferredStyle: UIAlertControllerStyle.Alert)

loginAlert.addTextFieldWithConfigurationHandler({
            textfield in
            textfield.placeholder = "Your username"
        })

        loginAlert.addTextFieldWithConfigurationHandler({
            textfield in
            textfield.placeholder = "Your password"
            textfield.secureTextEntry = true
        })

        loginAlert.addAction(UIAlertAction(title: "Login", style: UIAlertActionStyle.Default, handler: {
            alertAction in
            let textFields:NSArray = loginAlert.textFields as NSArray
            let usernameTextfield:UITextField = textFields.objectAtIndex(0) as UITextField
            let passwordTextfield:UITextField = textFields.objectAtIndex(1) as UITextField            
        }))
}

任何想法是什么问题？

Answer 1

“无法转换表达式的类型'[AnyObject]？”输入'NSArray'“

loginAlert.textFields之类的声音被定义为可选，可能是nil因此，如果您确定它不是nil，请先使用!打开它：

loginAlert.textFields as AnyObject! as NSArray

或：

loginAlert.textFields! as NSArray

在游乐场中非常基本的例子：

var temp:Array<String>?  // define Optional array 

temp = Array<String>()   // well, we create new Array but since its optional we need set "!" each time during manipulation

temp!.append("val1") // 1st off we unwrap it and add new value

var newArray = temp as AnyObject! as Array<String> // to downcast to Array<String>, we unwrap it with AnyObject! first

无法转换表达式的类型'[AnyObject]？'输入'NSArray'

1 个答案: