ios - swift ，线程 1 : EXC_BAD_INSTRUCTION error

Question

import UIKit

class ViewController: UIViewController {

@IBOutlet weak var currencySegment: UISegmentedControl!

@IBOutlet weak var sourceMoneyField: UITextField!

@IBOutlet weak var targetMoneyLabel: UILabel!

    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.
}
@IBAction func convertMoney(_ sender: Any) {
    let ratio : Double
    switch currencySegment.selectedSegmentIndex {
    case 0:
        ratio = 0.00085
    case 1:
        ratio = 1178.5
    default :
        ratio = 1.0
    }
    let targetMoneyString: String
    if let sourceMoney = Double(sourceMoneyField.text!){
        targetMoneyString = "\(sourceMoney * ratio)"
    }else {
        targetMoneyString = "Error"
    }

    targetMoneyLabel.text = targetMoneyString
}
}

在最后一部分，我得到的错误是:

thread 1: exc_bad_instruction(code=exc_i386_invop,subcode=0x0) error

到 targetMoneyLabel.text = targetMoneyString 部分。

我想我必须更改最后一句话，我尝试阅读和观看许多视频来修复它，但我做不到。

问题是否与nil有关？我是 Swift 的新手。

Answer 1

问题一定是关于展开变量。

你可以试试这个:

guard let targetMoneyString.characters.count > 0 else  {
    return
}
targetMoneyLabel.text = targetMoneyString