swift - 尝试连接字符串时出现 nill 错误

Question

我遵循了教程并正确完成了所有操作。就在我尝试设置标签文本时，我可以在控制台中打印出年龄，但出现 nil 错误。

class ViewController: UIViewController {


    @IBOutlet var inputField: UITextField!
    @IBOutlet var outputLbl: UILabel!

    @IBAction func enterBtn(sender: AnyObject) {

        if(inputField != nil){

           var age = inputField.text.toInt()
           println(age)

           var catYears = age! * 7
           println(catYears)
           outputLbl.text = "Your cat is \(catYears)  old"
        }
        else {            
           outputLbl.text = "Please enter a age"
        }
    }    

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

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

我阅读了文档并正确连接了字符串。然而就像我说的，当我取出下面的语句时:

outputLbl.text = "Your cat is \(catYears)  old"

程序运行良好。

Answer 1

我建议重构它以检查输入的文本是否能够转换为 int。您不应该检查 textField != nil 是否正确，因为如果 Storyboard正确加载，它不会为 nil。

考虑这个变化:

@IBAction func enterBtn(sender: UIButton) {

    if let age = inputField.text.toInt() {
        println(age)

        var catYears = age * 7
        println(catYears)
        outputLbl.text = "Your cat is \(catYears) old"
    } else {
        outputLbl.text = "Please enter a valid age"
    }
}