Don't destroy/recreate same items view controller during handoff

Reader.xcodeproj/project.pbxproj

@@ -7,6 +7,7 @@
 	objects = {
 
 /* Begin PBXBuildFile section */
+		D608238D27DE729E00D7D5F9 /* ItemListType.swift in Sources */ = {isa = PBXBuildFile; fileRef = D608238C27DE729E00D7D5F9 /* ItemListType.swift */; };
 		D65B18B22750469D004A9448 /* LoginViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D65B18B12750469D004A9448 /* LoginViewController.swift */; };
 		D65B18B4275048D9004A9448 /* ClientRegistration.swift in Sources */ = {isa = PBXBuildFile; fileRef = D65B18B3275048D9004A9448 /* ClientRegistration.swift */; };
 		D65B18B627504920004A9448 /* FervorController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D65B18B527504920004A9448 /* FervorController.swift */; };
@@ -116,6 +117,7 @@
 /* End PBXCopyFilesBuildPhase section */
 
 /* Begin PBXFileReference section */
+		D608238C27DE729E00D7D5F9 /* ItemListType.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ItemListType.swift; sourceTree = "<group>"; };
 		D65B18B12750469D004A9448 /* LoginViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = LoginViewController.swift; sourceTree = "<group>"; };
 		D65B18B3275048D9004A9448 /* ClientRegistration.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ClientRegistration.swift; sourceTree = "<group>"; };
 		D65B18B527504920004A9448 /* FervorController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = FervorController.swift; sourceTree = "<group>"; };
@@ -324,6 +326,7 @@
 				D68B303527907D9200E8B3FA /* ExcerptGenerator.swift */,
 				D68B304127932ED500E8B3FA /* UserActivities.swift */,
 				D68408EE2794808E00E327D2 /* Preferences.swift */,
+				D608238C27DE729E00D7D5F9 /* ItemListType.swift */,
 				D6A8A33527766E9300CCEC72 /* CoreData */,
 				D65B18AF2750468B004A9448 /* Screens */,
 				D6C687F7272CD27700874C10 /* Assets.xcassets */,
@@ -632,6 +635,7 @@
 			files = (
 				D6A8A33427766C2800CCEC72 /* PersistentContainer.swift in Sources */,
 				D6E24357278B96E40005E546 /* Feed+CoreDataClass.swift in Sources */,
+				D608238D27DE729E00D7D5F9 /* ItemListType.swift in Sources */,
 				D65B18B627504920004A9448 /* FervorController.swift in Sources */,
 				D68B304227932ED500E8B3FA /* UserActivities.swift in Sources */,
 				D6C687EC272CD27600874C10 /* AppDelegate.swift in Sources */,

Reader/ItemListType.swift

@@ -0,0 +1,60 @@
+//
+//  ItemListType.swift
+//  Reader
+//
+//  Created by Shadowfacts on 3/13/22.
+//
+
+import Foundation
+import CoreData
+
+enum ItemListType: Hashable {
+    case unread
+    case all
+    case group(Group)
+    case feed(Feed)
+    
+    var title: String {
+        switch self {
+        case .unread:
+            return "Unread Articles"
+        case .all:
+            return "All Articles"
+        case let .group(group):
+            return group.title
+        case let .feed(feed):
+            return feed.title!
+        }
+    }
+    
+    var idFetchRequest: NSFetchRequest<NSManagedObjectID> {
+        let req = NSFetchRequest<NSManagedObjectID>(entityName: "Item")
+        req.resultType = .managedObjectIDResultType
+        switch self {
+        case .unread:
+            req.predicate = NSPredicate(format: "read = NO")
+        case .all:
+            break
+        case .group(let group):
+            req.predicate = NSPredicate(format: "feed in %@", group.feeds!)
+        case .feed(let feed):
+            req.predicate = NSPredicate(format: "feed = %@", feed)
+        }
+        return req
+    }
+    
+    var countFetchRequest: NSFetchRequest<Reader.Item>? {
+        let req = Reader.Item.fetchRequest()
+        switch self {
+        case .unread:
+            req.predicate = NSPredicate(format: "read = NO")
+        case .all:
+            return nil
+        case .group(let group):
+            req.predicate = NSPredicate(format: "read = NO AND feed in %@", group.feeds!)
+        case .feed(let feed):
+            req.predicate = NSPredicate(format: "read = NO AND feed = %@", feed)
+        }
+        return req
+    }
+}

Reader/SceneDelegate.swift

@@ -119,9 +119,9 @@ class SceneDelegate: UIResponder, UIWindowSceneDelegate {
         }
         switch activity.activityType {
         case NSUserActivity.readUnreadType:
-            split.selectHomeItem(.unread)
+            split.showItemList(.unread)
         case NSUserActivity.readAllType:
-            split.selectHomeItem(.all)
+            split.showItemList(.all)
         case NSUserActivity.readFeedType:
             guard let feedID = activity.feedID() else {
                 break
@@ -129,7 +129,7 @@ class SceneDelegate: UIResponder, UIWindowSceneDelegate {
             let req = Feed.fetchRequest()
             req.predicate = NSPredicate(format: "id = %@", feedID)
             if let feed = try? fervorController.persistentContainer.viewContext.fetch(req).first {
-                split.selectHomeItem(.feed(feed))
+                split.showItemList(.feed(feed))
             }
         case NSUserActivity.readGroupType:
             guard let groupID = activity.groupID() else {
@@ -138,7 +138,7 @@ class SceneDelegate: UIResponder, UIWindowSceneDelegate {
             let req = Group.fetchRequest()
             req.predicate = NSPredicate(format: "id = %@", groupID)
             if let group = try? fervorController.persistentContainer.viewContext.fetch(req).first {
-                split.selectHomeItem(.group(group))
+                split.showItemList(.group(group))
             }
         default:
             break

Reader/Screens/AppSplitViewController.swift

@@ -54,7 +54,7 @@ class AppSplitViewController: UISplitViewController {
         setViewController(nav, for: .compact)
     }
     
-    func selectHomeItem(_ item: HomeViewController.Item) {
+    func showItemList(_ type: ItemListType) {
         let column: Column
         if traitCollection.horizontalSizeClass == .compact {
             column = .compact
@@ -63,7 +63,7 @@ class AppSplitViewController: UISplitViewController {
         }
         let nav = viewController(for: column) as! UINavigationController
         let home = nav.viewControllers.first! as! HomeViewController
-        home.selectItem(item)
+        home.selectItem(type)
     }
 
 }

Reader/Screens/Home/HomeViewController.swift

@@ -23,7 +23,7 @@ class HomeViewController: UIViewController {
     var enableStretchyMenu = true
     
     private var collectionView: UICollectionView!
-    private var dataSource: UICollectionViewDiffableDataSource<Section, Item>!
+    private var dataSource: UICollectionViewDiffableDataSource<Section, ItemListType>!
     private var groupResultsController: NSFetchedResultsController<Group>!
     private var feedResultsController: NSFetchedResultsController<Feed>!
     
@@ -76,7 +76,7 @@ class HomeViewController: UIViewController {
         
         dataSource = createDataSource()
         
-        var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
+        var snapshot = NSDiffableDataSourceSnapshot<Section, ItemListType>()
         snapshot.appendSections([.all, .groups, .feeds])
         snapshot.appendItems([.unread, .all], toSection: .all)
         dataSource.apply(snapshot, animatingDifferences: false)
@@ -116,14 +116,14 @@ class HomeViewController: UIViewController {
         dataSource.apply(snapshot)
     }
     
-    private func createDataSource() -> UICollectionViewDiffableDataSource<Section, Item> {
+    private func createDataSource() -> UICollectionViewDiffableDataSource<Section, ItemListType> {
         let sectionHeaderCell = UICollectionView.SupplementaryRegistration<UICollectionViewListCell>(elementKind: UICollectionView.elementKindSectionHeader) { supplementaryView, elementKind, indexPath in
             let section = self.dataSource.sectionIdentifier(for: indexPath.section)!
             var config = supplementaryView.defaultContentConfiguration()
             config.text = section.title
             supplementaryView.contentConfiguration = config
         }
-        let listCell = UICollectionView.CellRegistration<HomeCollectionViewCell, Item> { cell, indexPath, item in
+        let listCell = UICollectionView.CellRegistration<HomeCollectionViewCell, ItemListType> { cell, indexPath, item in
             var config = UIListContentConfiguration.valueCell()
             config.text = item.title
             if let req = item.countFetchRequest,
@@ -135,7 +135,7 @@ class HomeViewController: UIViewController {
             
             cell.accessories = [.disclosureIndicator()]
         }
-        let dataSource = UICollectionViewDiffableDataSource<Section, Item>(collectionView: collectionView) { collectionView, indexPath, item in
+        let dataSource = UICollectionViewDiffableDataSource<Section, ItemListType>(collectionView: collectionView) { collectionView, indexPath, item in
             return collectionView.dequeueConfiguredReusableCell(using: listCell, for: indexPath, item: item)
         }
         dataSource.supplementaryViewProvider = { collectionView, elementKind, indexPath in
@@ -206,26 +206,26 @@ class HomeViewController: UIViewController {
         }
     }
     
-    private func itemsViewController(for item: Item) -> ItemsViewController {
+    private func itemsViewController(for item: ItemListType) -> ItemsViewController {
-        let vc = ItemsViewController(fetchRequest: item.idFetchRequest, fervorController: fervorController)
+        let vc = ItemsViewController(type: item, fervorController: fervorController)
-        vc.title = item.title
         vc.delegate = itemsDelegate
-        switch item {
-        case .all:
-            vc.userActivity = .readAll(account: fervorController.account!)
-        case .unread:
-            vc.userActivity = .readUnread(account: fervorController.account!)
-        case .group(let group):
-            vc.userActivity = .readGroup(group, account: fervorController.account!)
-        case .feed(let feed):
-            vc.userActivity = .readFeed(feed, account: fervorController.account!)
-        }
         return vc
     }
     
-    func selectItem(_ item: Item) {
+    func selectItem(_ item: ItemListType) {
-        navigationController!.popToRootViewController(animated: false)
+        guard let navigationController = navigationController else {
-        navigationController!.pushViewController(itemsViewController(for: item), animated: false)
+            return
+        }
+        if navigationController.viewControllers.count >= 2,
+           let second = navigationController.viewControllers[1] as? ItemsViewController,
+           second.type == item {
+            while navigationController.viewControllers.count > 2 {
+                navigationController.popViewController(animated: false)
+            }
+        } else {
+            navigationController.popToRootViewController(animated: false)
+            navigationController.pushViewController(itemsViewController(for: item), animated: false)
+        }
     }
     
 }
@@ -247,56 +247,6 @@ extension HomeViewController {
             }
         }
     }
-    enum Item: Hashable {
-        case unread
-        case all
-        case group(Group)
-        case feed(Feed)
-        
-        var title: String {
-            switch self {
-            case .unread:
-                return "Unread Articles"
-            case .all:
-                return "All Articles"
-            case let .group(group):
-                return group.title
-            case let .feed(feed):
-                return feed.title!
-            }
-        }
-        
-        var idFetchRequest: NSFetchRequest<NSManagedObjectID> {
-            let req = NSFetchRequest<NSManagedObjectID>(entityName: "Item")
-            req.resultType = .managedObjectIDResultType
-            switch self {
-            case .unread:
-                req.predicate = NSPredicate(format: "read = NO")
-            case .all:
-                break
-            case .group(let group):
-                req.predicate = NSPredicate(format: "feed in %@", group.feeds!)
-            case .feed(let feed):
-                req.predicate = NSPredicate(format: "feed = %@", feed)
-            }
-            return req
-        }
-        
-        var countFetchRequest: NSFetchRequest<Reader.Item>? {
-            let req = Reader.Item.fetchRequest()
-            switch self {
-            case .unread:
-                req.predicate = NSPredicate(format: "read = NO")
-            case .all:
-                return nil
-            case .group(let group):
-                req.predicate = NSPredicate(format: "read = NO AND feed in %@", group.feeds!)
-            case .feed(let feed):
-                req.predicate = NSPredicate(format: "read = NO AND feed = %@", feed)
-            }
-            return req
-        }
-    }
 }
 
 extension HomeViewController: NSFetchedResultsControllerDelegate {

Reader/Screens/Items/ItemsViewController.swift

@@ -18,20 +18,32 @@ class ItemsViewController: UIViewController {
     weak var delegate: ItemsViewControllerDelegate?
     
     let fervorController: FervorController
-    let fetchRequest: NSFetchRequest<NSManagedObjectID>
+    let type: ItemListType
+    private let fetchRequest: NSFetchRequest<NSManagedObjectID>
     
     private var collectionView: UICollectionView!
     private var dataSource: UICollectionViewDiffableDataSource<Section, NSManagedObjectID>!
     
     private var batchUpdates: [() -> Void] = []
     
-    init(fetchRequest: NSFetchRequest<NSManagedObjectID>, fervorController: FervorController) {
+    init(type: ItemListType, fervorController: FervorController) {
-        precondition(fetchRequest.entityName == "Item")
-        
         self.fervorController = fervorController
-        self.fetchRequest = fetchRequest
+        self.type = type
+        self.fetchRequest = type.idFetchRequest
         
         super.init(nibName: nil, bundle: nil)
+        
+        self.title = type.title
+        switch type {
+        case .all:
+            self.userActivity = .readAll(account: fervorController.account!)
+        case .unread:
+            self.userActivity = .readUnread(account: fervorController.account!)
+        case .group(let group):
+            self.userActivity = .readGroup(group, account: fervorController.account!)
+        case .feed(let feed):
+            self.userActivity = .readFeed(feed, account: fervorController.account!)
+        }
     }
     
     required init?(coder: NSCoder) {