Unwind method doesn't work when using default backward button - ios

Question

I have three view controllers like below
I wrote the unwind method in viewcontroller1, and try to receive some data from viewcontroller2 and viewcontroller3 when they unwind to viewcontroller1.
#IBAction func unwindToViewController1(segue: UIStoryboardSegue) {
print("1")
main_content = (segue.source as! MainContentViewController).main_content
}
#IBAction func unwindToViewController2(segue: UIStoryboardSegue) {
print("2")
detailed_content = (segue.source as! SupplementContentViewController).supplement
}
And set the exit unwind segue for both controller 2 and 3 already.
But why the unwindToViewController methods never get called correctly? I think they should be called when I click the button automatically created by the system.

Answer 1

I solve this problem by using delegate instead of unwind. Delegate pattenr is a more explicit way to solve this problem.
By creating a protocol called myDelegate
protocol myDelegate {
func updateMaincontent(main_content : String)
func updateSupplement(supplement: String)
}
And create a delegate instance inside the second view controller
var delegate: myDelegate?
Then in the first view controller, make the class extend myDelegate and set this delegate of second view controller to self in the func prepare(for segue: UIStoryboardSegue, sender: Any?) method
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if let destinationViewController = segue.destination as? MainContentViewController {
destinationViewController.main_content = self.main_content
destinationViewController.delegate = self
}
else if let destinationViewController = segue.destination as? SupplementContentViewController {
destinationViewController.supplement = self.detailed_content
destinationViewController.delegate = self
}
}
Finally, go back to second view controller, and set the value of delegate to what you want in viewWillDisappear method.
func viewWillDisappear(_ animated: Bool) {
self.main_content = contentTextView.text
delegate?.updateMaincontent(main_content: contentTextView.text)
}