How to determine the last activ UITextField in Xcode - swift

Question

I am new to swift and i am playing around with a little converter app. I Have two TextFields and one "convert" button.
I want to overwrite the non acticv Textfield with the converted value from the last activ TextField.
I know it would be easier with more Textfields and more buttons but i would like to solve it this way.
Can anybody give me an advise?
var NumberC = Int(InputCelcius.text!)!
var NumberF = Int(InputFahrenheit.text!)!
if InputCelcius.isFirstResponder {
if (InputCelcius.text?.isEmpty)! {
NumberC=0
print("NumberC is empty")
}
NumberC = NumberC * 9/5 + 32
InputFahrenheit.text = " \(NumberC)"
}
else if InputFahrenheit.isFirstResponder {
if (InputFahrenheit.text?.isEmpty)! {
NumberF=0
print("NumberF is empty")
}
NumberF = (NumberF - 32) * 5/9
InputCelcius.text = " \(NumberF)"
}

Answer 1

I’d suggest using the UITextFieldDelegate function textFieldDidEndEditing. Make sure you subclass your viewController as a UITextFieldDelegate.
class ViewController: UIViewController, UITextFieldDelegate {
Set each textField's delegate to self in viewDidLoad.
override func viewDidLoad() {
super.viewDidLoad()
InputFahrenheit.delegate = self
InputCelsius.delegate = self
}
With this method you wouldn't even need a UIButton, but you could use the button to force the textField to end editing like this.
#objc func buttonAction (sender: UIButton) {
self.view.endEditing(true)
}
Which will call this delegate method if the user was editing a textField.
func textFieldDidEndEditing (textField: UITextField) {
if textField.isEmpty {return} //this prevents nil errors and user would have to type in "0" if wishing to convert zero.
if textField == InputCelsius {
let conversion = Float(textField.text!) * 9/5 + 32
InputFahrenheit.text = String(format: “%.f”, conversion) //“%.1f” will show one decimal place and so forth
} else if textField == InputFahrenheit {
let conversion = ( Float(textField.text!) - 32 ) * 5/9
InputCelsius.text = String(format: “%.f”, conversion)
}
}

Answer 2

I‘m not quite sure about that but I think if you press the button, the button itself will become first responder, so your code won‘t work.
The proper way to do that, would be to set IBAction functions that get called when you finish editing one of your textfields. Just connect the Textfields inside your storyboard to the code like you did it with your button.
Then you can set up two functions, one for each of the textfields, so you don‘t have to worry about firstresponder.