How to prevent a UIViewController from being popped out? - ios

Question

I have a childViewController which is pushed from parentViewController. In childViewController I want to block pop action in a particular condition.
I wrote this code in viewWillDisappear: But I guess need to do this somewhere else.
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
if changesMade {
let alertController = UIAlertController(title: "Alert", message: "Changes made are not saved. Do you wish to save changes made?", preferredStyle: .alert)
let cancelOption = UIAlertAction(title: "Cancel", style: .cancel)
let saveOption = UIAlertAction(title: "Save", style: .default, handler: { (action) in
self.saveSession()
})
alertController.addAction(saveOption)
alertController.addAction(cancelOption)
present(alertController, animated: true)
}
}

Answer 1

Actually, there is a very simple solution: navigationItem.hidesBackButton = true - this will hide "BACK" button and disable swipe-to-back feature. 🤓

Answer 2

There are two cases here:
User can pop using back button.
User can pop using interactive pop gesture of navigation controller.
I think you should use a custom back button and name it Done and write your logic of showing alert on press of this button.
Using the custom back button would disable the interactive pop gesture by default and you will be spared from playing the dance of enabling/disabling interactivePopGesture on navigation controller.

Answer 3

block pop action till your changes are not saved like this
if changesMade {
let alertController = UIAlertController(title: "Alert", message: "Changes made are not saved. Do you wish to save changes made?", preferredStyle: .alert)
let cancelOption = UIAlertAction(title: "Cancel", style: .cancel)
let saveOption = UIAlertAction(title: "Save", style: .default, handler: { (action) in
self.saveSession()
self.navigationController?.popViewController(animated: true)
})
alertController.addAction(saveOption)
alertController.addAction(cancelOption)
present(alertController, animated: true)
}
Update - Add this below custom button and its action in child View controller which is being pushed from parent View Controller
so, without satisfying your condition user can not move from child to parent again
For customising action of navigation backButton you need to manually add a back Button using below line , you can Customise barButton being added here in DidLoad
self.navigationItem.leftBarButtonItem = UIBarButtonItem(title: "Back", style: UIBarButtonItemStyle.plain, target: self, action: #selector(self.backToInitial(sender:)))
It will perform required Action
#objc func backToInitial(sender: AnyObject) {
if changesMade {
let alertController = UIAlertController(title: "Alert", message: "Changes made are not saved. Do you wish to save changes made?", preferredStyle: .alert)
let cancelOption = UIAlertAction(title: "Cancel", style: .cancel)
let saveOption = UIAlertAction(title: "Save", style: .default, handler: { (action) in
self.saveSession()
self.navigationController?.popViewController(animated: true)
})
alertController.addAction(saveOption)
alertController.addAction(cancelOption)
present(alertController, animated: true)
}
}
and I do not think you can stop default back button action task of navigation Controller as it is designed the way to perform it
But yes you can manage it in ViewWillDisappear as :
override func viewWillDisappear(_ animated: Bool) {
if self.isMovingFromParentViewController || self.isBeingDismissed {
self.navigationController?.popViewController(animated: false) //here task but will not result as Expected output
}
}
-----------------Re-Update ---------------
in swift I used a objective-C class to get output as expected now, childViewController pop action is being controller from a alert using default back button that we get from navigation controller
You can customise you pop action to perform or not until your condition is not satisfied
Github Link - https://github.com/RockinGarg/NavigationBackButton.git

Answer 4

I found a much more elegant solution (in my opinion).
It works no matter how the user triggers the pop (accessibility escape, swipe back gesture, tapping back) since it overrides the built in pop methods that the system uses.
Swift 5
public class DiscardSafeNavigationController:UINavigationController {
/// Should the pop be prevented? Set this to `true` when you have changes which need to be protected
public var hasUnsavedChanges:Bool = false
/// Show a prompt on the top most screen asking the user if they wish to proceed with the pop
/// - Parameter discardCallback: The callback to use if the user opts to discard
private func confirmDiscardChanges(discardCallback:#escaping (()->())) {
let alertController = UIAlertController.init(title: "Discard changes", message: "Are you sure you want to discard any unsaved changes?", preferredStyle: UIAlertController.Style.alert)
alertController.addAction(UIAlertAction.init(title: "Discard", style: UIAlertAction.Style.destructive, handler: { (_) in
discardCallback()
//User elected to discard and so, at this point, they no longer have changes to save
self.hasUnsavedChanges = false
}))
alertController.addAction(UIAlertAction.init(title: "Cancel", style: UIAlertAction.Style.cancel, handler: nil))
self.topViewController?.present(alertController, animated: true, completion: nil)
}
override func popViewController(animated: Bool) -> UIViewController? {
//If there aren't unsaved changes, popping is safe
if !hasUnsavedChanges {
return super.popViewController(animated: animated)
}else {
//Changes have been made. Block the pop and first check with the user before continuing
confirmDiscardChanges {
super.popViewController(animated: animated)
}
return nil
}
}
}
and when you want to enable discard protection from any child view controllers, simply use:
(self.navigationController as? DiscardSafeNavigationController)?.hasUnsavedChanges = true
and then any time the navigation controller is asked to pop it, the navigation controller will ask the user first.