仅当两个文本字段都填写时，如何在 Swift 中添加两个数字

Question

I'm trying to add two numbers in Swift 5, and I want to add some error checks. I don't want to make it possible for a user to click on the plus button if both of the text fields are not filled in. I tried with the if state below but it did not work.

the whole function:

@IBAction func sum(_ sender: Any) {

      let one = input1.text
      let oneInt = Int(one!)
      let two = input2.text
      let twoInt = Int(two!)
      let total = oneInt! + twoInt!
      label.text = "\(total)"

    if(input2.text == nil){
        addBtn.isEnabled = false
    }
    if(input1.text == nil){
        addBtn.isEnabled = false
    }
  }

Answer 1

try to use guard like this.If your input field does not contain any value that field return blank string and when you try to get integer value from that string it will return nil and your add button will be disable.

@IBAction func sum(_ sender: Any) {

  guard let text1 = input1.text, let intValue1 = Int(text1) else {
  addBtn.isEnabled = false
  return "error"
 }
 guard let text2 = input2.text, let intValue2 = Int(text2) else {
  addBtn.isEnabled = false 
  return "error"
 }
label.text = "\(intValue1 + intValue2)"

}

Answer 2

A nice and simple way is to addTarget to your textFiels . This will enable you to handle the events on the text field. In this scenario we'll use .editingChanged and use a single selector to achieve our goal:

What we'll do : We will listen for when someone types something in the textfield. Whenever a text changed was made, we'll check to see if all the textfields was populated and then if it was we enable the sum button.

A small controller sample :: Make sure to read the comments to understand the code faster

import UIKit

class ViewController: UIViewController {
    @IBOutlet var textfield1: UITextField!
    @IBOutlet var textfield2: UITextField!
    @IBOutlet var sumButton: UIButton!
    @IBOutlet weak var label: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()
        sumButton.isEnabled = false /// Disable the button first thing
        [textfield1, textfield2].forEach {
            $0.addTarget(self, action: #selector(editingChanged(_:)), for: .editingChanged) /// add targets to handle the events (in your case it listens for the 'editingChanged' event )
        }
    }

    @objc func editingChanged(_ textField: UITextField) {

        /// Here we just loop through all our textfields 
        for each in  [textfield1, textfield2] {
            if let text = each?.text { /// Just make sure the textfields text is not nil
                if text.count < 1 {
                    // If the textfiels text has no value in, then we keep the button disabled and return
                    sumButton.isEnabled = false
                    return
                }
            } else {
                /// Else if the text field's text is nill, then return and keep the button disabled
                sumButton.isEnabled = false
                return
            }
        }

        sumButton.isEnabled = true /// If the code reaches this point, it means the textfields passed all out checks and the button can be enabled
    }

    @IBAction func sum(_ sender: Any) {
        let one = textfield1.text!
        let two = textfield2.text!

        guard let oneInt = Int(one), let twoInt = Int(two) else {
            print("Whatever was in that text fields, couldn't be converted to an Int")
            label.text = "Be sure to add numbers."
            return
        }

        let total = oneInt + twoInt

        label.text = "\(total)"
    }
}

Answer 3

textfields are not nil but empty strings. so make your comparison like :

if input1.text == "" { 
 // do your check here 
}

Answer 4

Seems like you want to start with addBtn.isEnabled = false then update it whenever the user enters two valid integers into the text fields, ie Int(input1.text ?? "") != nil && Int(input2.text ?? "") != nil . You can do this by adding a target to your textfields ( input1 and input2 ) for .editingChanged events. For example, if you're doing this in a UIViewController , you can do this in viewDidLoad :

    override func viewDidLoad() {
        super.viewDidLoad()
        addBtn.isEnabled = false
        input1.addTarget(self, action: #selector(textFieldDidEdit(_:)), for: .editingChanged)
        input2.addTarget(self, action: #selector(textFieldDidEdit(_:)), for: .editingChanged)
    }

Where textFieldDidEdit(_:) action looks like:

    @objc func textFieldDidEdit(_ sender: UITextField) {
        addBtn.isEnabled = Int(input1.text ?? "") != nil && Int(input2.text ?? "") != nil
    }

Finally your sum function becomes:

   @IBAction func sum(_ sender: UIButton) {
        guard let oneInt = Int(input1.text ?? ""), let twoInt = Int(input2.text ?? "") else {
            return
        }
        let total = oneInt + twoInt
        label.text = "\(total)"
    }

As all of the number validation has moved to the textFieldDidEdit(_:) function.