首先，很抱歉，因为我已将其放在平板电脑上，这意味着我无法访问代码编辑器。但是，这是我对您的问题的看法：
@IBOutlet weak var testLabel: UILabel!
@IBOutlet weak var first: UITextField!
@IBOutlet weak var second: UITextField!
func calculation1() -> Void {
// Check our two text fields contain text
guard let _ = first.text,
let _ = second.text else { return }
c // Check that the text can be parsed as Doubles
c guard let dfirst : Double = Double(first.text!),
let dsecond : Double = Double(second.text!) else { return }
// Now that we know we have two valid numbers, do the calculation
let answerCal : Double = ceil(dfirst! * dsecond!)
// Fetch a number formatter
let numberFormatter : NSNumberFormatter = {
let nF : NSNumberFormatter = NSNumberFormatter()
nF.numberStyle = .DecimalStyle
return nF
}()
// And update the text field with the answer if it produces a valid result
if let answerText : String = numberFormatter.stringFromNumber(answerCal) {
testLabel.text = answerText
}
}
您必须小心使用 UI 元素，如果您不先检查，用户理论上可以输入任何内容并导致您的应用程序崩溃。因此，如果文本字段中没有文本或这些字段包含不可用的文本，则保护语句将安全地退出方法调用。
您从数字格式化程序返回 Optional 的原因是因为无法保证格式化程序能够为您提供有效的字符串。因此，您会看到，在尝试更新文本字段之前，我已经明确检查了 numbe 格式化程序是否会生成非零结果。
（注意 - 我很欣赏数字格式化程序的关闭在技术上超出了要求，但我发现有时在配置对象时更清楚。）
更新：
Vidal - 你试过我发给你的代码了吗？我很快就根据我昨晚整理的内容整理了以下内容。这显然很粗糙，但表明我建议的方法效果很好，除非我遗漏了什么。我能想到的唯一问题是您在界面构建器中做了一些我不知道的事情。希望对您有所帮助！
import UIKit
class ViewController: UIViewController {
var calculatorView : UIView!
var textFieldOne : UITextField!
var textFieldTwo : UITextField!
var calButton : UIButton!
var answer : UILabel!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
self.calculatorView = {
let cV : UIView = UIView(frame: CGRect(origin: CGPointZero, size: CGSizeMake(400, 400)))
cV.backgroundColor = UIColor.redColor()
func buildTextField() -> UITextField {
let tF : UITextField = UITextField()
tF.backgroundColor = UIColor.whiteColor()
tF.textColor = UIColor.blackColor()
tF.placeholder = "Please enter number"
return tF
}
self.textFieldOne = buildTextField()
self.textFieldTwo = buildTextField()
self.textFieldOne.frame = CGRect(origin: CGPointMake(20, 20), size: CGSizeMake(160, 50))
self.textFieldTwo.frame = CGRect(origin: CGPointMake(220, 20), size: CGSizeMake(160, 50))
self.calButton = {
let cB : UIButton = UIButton()
cB.setTitle("Calculate", forState: .Normal)
cB.frame = CGRect(origin: CGPointMake(20, 80), size: CGSizeMake(360, 50))
cB.addTarget(self, action: #selector(self.getAnswer), forControlEvents: UIControlEvents.TouchUpInside)
return cB
}()
self.answer = {
let a : UILabel = UILabel()
a.backgroundColor = UIColor.blueColor()
a.textColor = UIColor.whiteColor()
a.frame = CGRect(origin: CGPointMake(20, 140), size: CGSizeMake(360, 50))
return a
}()
cV.addSubview(textFieldOne)
cV.addSubview(textFieldTwo)
cV.addSubview(calButton)
cV.addSubview(answer)
return cV
}()
self.view.addSubview(calculatorView)
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
func getAnswer() -> Void {
// Check our two text fields contain text
guard let _ = self.textFieldOne.text,
let _ = self.textFieldTwo.text else { return }
// Check that the text can be parsed as Doubles
guard let dfirst : Double = Double(self.textFieldOne.text!),
let dsecond : Double = Double(self.textFieldTwo.text!) else { return }
// Now that we know we have two valid numbers, do the calculation
let answerCal : Double = ceil(dfirst * dsecond)
// Fetch a number formatter
let numberFormatter : NSNumberFormatter = {
let nF : NSNumberFormatter = NSNumberFormatter()
nF.numberStyle = .DecimalStyle
return nF
}()
// And update the text field with the answer if it produces a valid result
if let answerText : String = numberFormatter.stringFromNumber(answerCal) {
self.answer.text = answerText
}
}
}