Populating information in swift 3 for iPad

You could implement UITextFieldDelegate and your delegate will be called when the user enter something in your text field.

1. First set the delegate to self

   txtField.delegate = self
   

2. Use this if you want to change the other fields when the user is done editiing your master field

   func textFieldDidEndEditing(_ textField: UITextField, reason: UITextFieldDidEndEditingReason) {
      // change other fields here
      otherField.text = textField.text
   }