Prevent View Disappearing in splitview When User Edits Pending Swift 3 - ios

Question

I have a universal master-detail application where I present the master
and detail views side by side on an iPad in both orientations. When a
user makes changes in the detail view on an iPhone I can easily detect
changes and present an alert asking if they want to save the changes or
lose them (CoreData). On an iPad, there is no prohibition against simply clicking
in the master list thereby losing the edits.
I have placed a function in the DetailViewController viewWillDisappear
(for iPad) that raises an alert, but the compiler tells me that it does
not like the presentation of a view on a non-connected view.
Console message: Presenting view controllers on detached view
controllers is discouraged <>.
Is there a more appropriate way to handle this? Swift 3, iOS 10, Xcode 8.2.1
var hasChanged //set to true whenever edits are made
override func viewWillDisappear(_ animated: Bool) {
if UIDevice.current.model == "iPad" {
if hasChanged {
print("hasChanged (should be true) is: \(hasChanged)")
cancelUnsavedEdits()
}//if hasChanged
}//if ipad
}//viewWillDisappear
func cancelUnsavedEdits() {
if hasChanged {
let ac = UIAlertController(title: nil, message: nil, preferredStyle: .alert)
ac.addAction(UIAlertAction(title: "Delete Edits", style: .default, handler: { (action : UIAlertAction!) -> Void in
self.codeDismissTheKeyboard()
self.performSegue(withIdentifier: "unwindToMasterViewController", sender: self)
let editRecordButton = UIBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.edit, target: self, action: #selector(DetailViewController.editThisRecord))
self.navigationItem.rightBarButtonItem = editRecordButton
self.navigationItem.leftBarButtonItem = nil
self.navigationItem.hidesBackButton = false
//need to remove the edits - refresh the original page
self.configureView()
}))//addAction block
ac.addAction(UIAlertAction(title: "Save Edits", style: .default, handler: { (action : UIAlertAction!) -> Void in
self.codeDismissTheKeyboard()
self.saveTheEditedRecord()
self.performSegue(withIdentifier: "unwindToMasterViewController", sender: self)
}))//addAction block
//ac.addAction(UIAlertAction(title: "Cancel", style: .default, handler: nil))
//try this - for -ipad add code in handler to reopen the fields for editing if the cancel of the cancel is chosen
ac.addAction(UIAlertAction(title: "Cancel", style: .default, handler: { (whatever) in
self.makeEntryFieldsEnabledYES()
let cancelItemButton = UIBarButtonItem(barButtonSystemItem: .cancel, target: self, action: #selector(DetailViewController.cancelUnsavedEdits))
self.navigationItem.leftBarButtonItem = cancelItemButton
}))
//try above
self.present(ac, animated: true, completion: nil)
} else {
self.codeDismissTheKeyboard()
//for ipad
self.navigationItem.rightBarButtonItem = nil
self.performSegue(withIdentifier: "unwindToMasterViewController", sender: self)
}//if hasChanged
//for ipad
navigationItem.leftBarButtonItem = nil
}//cancelUnsavedEdits

Answer 1

I think the problem you try to present a new viewController on a viewController which is going to be removed from the view hierarchy.
Maybe a dirty fix can be to replace:
self.present(ac, animated: true, completion: nil)
to:
self.view.window.rootViewController?.present(ac, animated: true, completion: nil);