Add no content message to list timelines

Closes #215

Also fix interactive dismissal of edit screen not reloading list

Tusker/Screens/Lists/ListTimelineViewController.swift

@@ -16,6 +16,8 @@ class ListTimelineViewController: TimelineViewController {
     
     var presentEditOnAppear = false
     
+    private var noContentView: UIStackView!
+    
     private var listRenamedCancellable: AnyCancellable?
     
     init(for list: List, mastodonController: MastodonController) {
@@ -53,6 +55,39 @@ class ListTimelineViewController: TimelineViewController {
         }
     }
     
+    private func createNoContentView() {
+        let title = UILabel()
+        title.textColor = .secondaryLabel
+        title.font = .preferredFont(forTextStyle: .title1).withTraits(.traitBold)!
+        title.adjustsFontForContentSizeCategory = true
+        title.text = "No Posts"
+        
+        let subtitle = UILabel()
+        subtitle.textColor = .secondaryLabel
+        subtitle.font = .preferredFont(forTextStyle: .body)
+        subtitle.adjustsFontForContentSizeCategory = true
+        subtitle.numberOfLines = 0
+        subtitle.textAlignment = .center
+        subtitle.text = "This list doesn't currently have any posts. Edit it to add accounts if necessary."
+        
+        noContentView = UIStackView(arrangedSubviews: [
+            title,
+            subtitle,
+        ])
+        noContentView.axis = .vertical
+        noContentView.spacing = 8
+        noContentView.alignment = .center
+        noContentView.isAccessibilityElement = true
+        noContentView.accessibilityLabel = subtitle.text
+        noContentView.translatesAutoresizingMaskIntoConstraints = false
+        view.addSubview(noContentView)
+        NSLayoutConstraint.activate([
+            noContentView.centerYAnchor.constraint(equalTo: view.centerYAnchor),
+            noContentView.leadingAnchor.constraint(equalToSystemSpacingAfter: view.safeAreaLayoutGuide.leadingAnchor, multiplier: 1),
+            view.safeAreaLayoutGuide.trailingAnchor.constraint(equalToSystemSpacingAfter: noContentView.trailingAnchor, multiplier: 1),
+        ])
+    }
+    
     private func listChanged() {
         title = list.title
     }
@@ -61,10 +96,23 @@ class ListTimelineViewController: TimelineViewController {
         let editListAccountsController = EditListAccountsViewController(list: list, mastodonController: mastodonController)
         editListAccountsController.navigationItem.rightBarButtonItem = UIBarButtonItem(barButtonSystemItem: .done, target: self, action: #selector(editListDoneButtonPressed))
         let navController = UINavigationController(rootViewController: editListAccountsController)
+        navController.sheetPresentationController?.delegate = self
         present(navController, animated: animated)
     }
     
-    // MARK: - Interaction
+    private func reloadIfNecessary(editViewController: EditListAccountsViewController) {
+        guard editViewController.changedAccounts else {
+            return
+        }
+        noContentView?.removeFromSuperview()
+        noContentView = nil
+        Task {
+            applyInitialSnapshot()
+            await controller.loadInitial()
+        }
+    }
+    
+    // MARK: Interaction
     
     @objc func editListButtonPressed() {
         presentEdit(animated: true)
@@ -75,12 +123,28 @@ class ListTimelineViewController: TimelineViewController {
         
         dismiss(animated: true)
         
-        if presented?.changedAccounts == true {
-            Task {
-                applyInitialSnapshot()
-                await controller.loadInitial()
-            }
+        if let presented {
+            self.reloadIfNecessary(editViewController: presented)
         }
     }
     
+    // MARK: TimelineLikeControllerDelegate
+    
+    override func handleReplaceAllItems(_ timelineItems: [String]) async {
+        if timelineItems.isEmpty {
+            createNoContentView()
+        }
+        await super.handleReplaceAllItems(timelineItems)
+    }
+
+}
+
+extension ListTimelineViewController: UISheetPresentationControllerDelegate {
+    func presentationControllerWillDismiss(_ presentationController: UIPresentationController) {
+        guard let nav = presentationController.presentedViewController as? UINavigationController,
+              let edit = nav.viewControllers.first as? EditListAccountsViewController else {
+            return
+        }
+        reloadIfNecessary(editViewController: edit)
+    }
 }

Tusker/Screens/Timeline/TimelineViewController.swift

@@ -1016,6 +1016,18 @@ class TimelineViewController: UIViewController, TimelineLikeCollectionViewContro
         }
         self.showToast(configuration: config, animated: true)
     }    
+    
+    // this is copied from the TimelineLikeCollectionViewController implementation because it needs to be overridable by ListTimelineViewController
+    func handleReplaceAllItems(_ timelineItems: [String]) async {
+        var snapshot = dataSource.snapshot()
+        if snapshot.sectionIdentifiers.contains(.entries) {
+            snapshot.deleteSections([.entries])
+        }
+        snapshot.appendSections([.entries])
+        snapshot.appendItems(timelineItems.map { .fromTimelineItem($0) }, toSection: .entries)
+        await apply(snapshot, animatingDifferences: false)
+    }
+
 }
 
 extension TimelineViewController {