在重新审视似乎与Xcode6 beta 5一起使用的代码时，我注意到我得到一个“无法转换表达式的类型”[AnyObject]？为此行键入“NSArray”错误：
let textFields:NSArray = loginAlert.textFields as NSArray
这是代码似乎是问题的部分：
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？
“Cannot convert the expression’s type ‘[AnyObject]?’ to type ‘NSArray'”
听起来像loginAlert.textFields被定义为可选，可能是零，因此如果你确定它不是零 – 首先使用！打开它：
loginAlert.textFields as AnyObject! as NSArray
要么：
loginAlert.textFields! as NSArray
操场上相当基本的例子：
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
