@@ -27,6 +27,14 @@ class CustomListViewController: UIViewController {
2727 private let alertPresenter : AlertPresenter
2828 private var validationErrors : Set < CustomListFieldValidationError > = [ ]
2929
30+ private var persistedCustomList : CustomList ? {
31+ return interactor. fetchAll ( ) . first ( where: { $0. id == subject. value. id } )
32+ }
33+
34+ private var customListHasUnsavedChanges : Bool {
35+ return persistedCustomList != subject. value. customList
36+ }
37+
3038 private lazy var cellConfiguration : CustomListCellConfiguration = {
3139 CustomListCellConfiguration ( tableView: tableView, subject: subject)
3240 } ( )
@@ -91,9 +99,37 @@ class CustomListViewController: UIViewController {
9199 }
92100
93101 private func configureNavigationItem( ) {
102+ if let navigationController = navigationController as? InterceptibleNavigationController {
103+ interceptNavigation ( navigationController)
104+ }
105+
94106 navigationItem. rightBarButtonItem = saveBarButton
95107 }
96108
109+ private func interceptNavigation( _ navigationController: InterceptibleNavigationController ) {
110+ navigationController. shouldPopViewController = { [ weak self] viewController in
111+ guard
112+ let self,
113+ viewController is Self ,
114+ customListHasUnsavedChanges
115+ else { return true }
116+
117+ self . onUnsavedChanges ( )
118+ return false
119+ }
120+
121+ navigationController. shouldPopToViewController = { [ weak self] viewController in
122+ guard
123+ let self,
124+ viewController is ListCustomListViewController ,
125+ customListHasUnsavedChanges
126+ else { return true }
127+
128+ self . onUnsavedChanges ( )
129+ return false
130+ }
131+ }
132+
97133 private func configureTableView( ) {
98134 tableView. delegate = dataSourceConfiguration
99135 tableView. backgroundColor = . secondaryColor
@@ -195,4 +231,51 @@ class CustomListViewController: UIViewController {
195231
196232 alertPresenter. showAlert ( presentation: presentation, animated: true )
197233 }
234+
235+ @objc private func onUnsavedChanges( ) {
236+ let message = NSMutableAttributedString (
237+ markdownString: NSLocalizedString (
238+ " CUSTOM_LISTS_UNSAVED_CHANGES_PROMPT " ,
239+ tableName: " CustomLists " ,
240+ value: " You have unsaved changes. " ,
241+ comment: " "
242+ ) ,
243+ options: MarkdownStylingOptions ( font: . preferredFont( forTextStyle: . body) )
244+ )
245+
246+ let presentation = AlertPresentation (
247+ id: " api-custom-lists-unsaved-changes-alert " ,
248+ icon: . alert,
249+ attributedMessage: message,
250+ buttons: [
251+ AlertAction (
252+ title: NSLocalizedString (
253+ " CUSTOM_LISTS_DISCARD_CHANGES_BUTTON " ,
254+ tableName: " CustomLists " ,
255+ value: " Discard changes " ,
256+ comment: " "
257+ ) ,
258+ style: . destructive,
259+ handler: {
260+ // Reset subject/view model to no longer having unsaved changes.
261+ if let persistedCustomList = self . persistedCustomList {
262+ self . subject. value. update ( with: persistedCustomList)
263+ }
264+ self . delegate? . customListDidSave ( self . subject. value. customList)
265+ }
266+ ) ,
267+ AlertAction (
268+ title: NSLocalizedString (
269+ " CUSTOM_LISTS_BACK_TO_EDITING_BUTTON " ,
270+ tableName: " CustomLists " ,
271+ value: " Back to editing " ,
272+ comment: " "
273+ ) ,
274+ style: . default
275+ ) ,
276+ ]
277+ )
278+
279+ alertPresenter. showAlert ( presentation: presentation, animated: true )
280+ }
198281}
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