ios - fatal error : unexpectedly found nil while unwrapping an Optional value Computation

Question

import UIKit

class ViewController: UIViewController {

@IBOutlet weak var yourScore: UITextField!
@IBOutlet weak var totalScore: UITextField!
@IBOutlet weak var labelText: UILabel!
@IBAction func buttonPressed(sender: AnyObject) {
    let score1: Int = yourScore.text.toInt()!
    let score2: Int = totalScore.text.toInt()!
    let mistakes = score2 - score1
    let scoreFinal = ((((score2 / 2) - mistakes)*23)/score2)+75
    labelText.text = "\(scoreFinal)"
}
override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
}

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


}

我的代码有问题。是因为数据类型还是什么？当我加载应用程序时，它可以正常打开，但是当按下按钮时，应用程序崩溃了。

http://i.stack.imgur.com/B2i5Z.png

Answer 1

您可以使用 if let 安全地解包值:

if let score1 = yourScore.text.toInt() {
    if let score2 = totalScore.text.toInt() {
        let mistakes = score2 - score1
        let scoreFinal = ((((score2 / 2) - mistakes)*23)/score2)+75
        labelText.text = "\(scoreFinal)"
    } else {
        // no valid score2
    }
} else {
    // no valid score1
}