RCOCOA-2105 Fix crash when deleting a row from @ObservedSectionedResu…

…lts (#8295)

CHANGELOG.md

@@ -1,11 +1,12 @@
 x.y.z Release notes (yyyy-MM-dd)
 =============================================================
 ### Enhancements
-* None.
+* Add `@ObservedSectionedResults.remove(atOffsets:section:)` which adds the ability to 
+  remove a Realm Object when using `onDelete` on `ForEach` in a SwiftUI `List`.
 
 ### Fixed
-* <How to hit and notice issue? what was the impact?> ([#????](https://github.com/realm/realm-swift/issues/????), since v?.?.?)
-* None.
+* Deleting a Realm Object used in a `@ObservedSectionedResults` collection in `SwiftUI`
+  would cause a crash during the diff on the `View`. ([#8294](https://github.com/realm/realm-swift/issues/8294), since v10.29.0)
 
 <!-- ### Breaking Changes - ONLY INCLUDE FOR NEW MAJOR version -->
 

Realm/Tests/SwiftUITestHost/SwiftUITestHostApp.swift

@@ -374,6 +374,8 @@ struct ObservedSectionedResultsKeyPathTestView: View {
                     Section(header: Text(section.key)) {
                         ForEach(section) { object in
                             ObservedResultsKeyPathTestRow(list: object)
+                        }.onDelete {
+                            $reminders.remove(atOffsets: $0, section: section)
                         }
                     }
                 }
@@ -443,10 +445,10 @@ struct ObservedSectionedResultsSearchableTestView: View {
             .navigationTitle("Reminders")
             .navigationBarItems(trailing:
                 Button("add") {
-                let realm = $reminders.wrappedValue.realm
-                try! realm?.write {
-                    realm?.add(ReminderList())
-                }
+                    let realm = $reminders.wrappedValue.realm?.thaw()
+                    try! realm?.write {
+                        realm?.add(ReminderList())
+                    }
                 }.accessibility(identifier: "addList"))
         }
     }
@@ -488,15 +490,15 @@ struct ObservedSectionedResultsConfiguration: View {
             .navigationTitle("Reminders")
             .navigationBarItems(leading:
                 Button("add A") {
-                    let realm = $remindersA.wrappedValue.realm
+                    let realm = $remindersA.wrappedValue.realm?.thaw()
                     try! realm?.write {
                         realm?.add(ReminderList())
                     }
                 }.accessibility(identifier: "addListA")
             )
             .navigationBarItems(trailing:
                 Button("add B") {
-                    let realm = $remindersB.wrappedValue.realm
+                    let realm = $remindersB.wrappedValue.realm?.thaw()
                     try! realm?.write {
                         realm?.add(ReminderList())
                     }

Realm/Tests/SwiftUITestHostUITests/SwiftUITestHostUITests.swift

@@ -440,6 +440,22 @@ class SwiftUITests: XCTestCase {
             XCTAssertEqual(app.tables.firstMatch.cells.count, 3)
         }
         XCTAssertEqual(realm.objects(ReminderList.self).count, 3)
+
+        let collectionViewsQuery = XCUIApplication().collectionViews
+        collectionViewsQuery.children(matching: .other).element(boundBy: 1).tap()
+        collectionViewsQuery.children(matching: .cell).element(boundBy: 1).children(matching: .other).element(boundBy: 1).children(matching: .other).element.swipeLeft()
+        collectionViewsQuery.buttons["Delete"].tap()
+        XCTAssertEqual(realm.objects(ReminderList.self).count, 2)
+
+        collectionViewsQuery.children(matching: .other).element(boundBy: 2).tap()
+        collectionViewsQuery.children(matching: .cell).element(boundBy: 2).children(matching: .other).element(boundBy: 1).children(matching: .other).element.swipeLeft()
+        collectionViewsQuery.buttons["Delete"].tap()
+        XCTAssertEqual(realm.objects(ReminderList.self).count, 1)
+
+        collectionViewsQuery.children(matching: .other).element(boundBy: 1).tap()
+        collectionViewsQuery.children(matching: .cell).element(boundBy: 1).children(matching: .other).element(boundBy: 1).children(matching: .other).element.swipeLeft()
+        collectionViewsQuery.buttons["Delete"].tap()
+        XCTAssertEqual(realm.objects(ReminderList.self).count, 0)
     }
 
     @MainActor

RealmSwift/SwiftUI.swift

@@ -644,7 +644,10 @@ extension Projection: _ObservedResultsValue { }
 @propertyWrapper public struct ObservedSectionedResults<Key: _Persistable & Hashable, ResultType>: DynamicProperty, BoundCollection where ResultType: _ObservedResultsValue & RealmFetchable & KeypathSortable & Identifiable {
     public typealias Element = ResultType
 
-    private class Storage: ObservableResultsStorage<SectionedResults<Key, ResultType>> {
+    private class Storage: ObservableResultsStorage<Results<ResultType>> {
+        var sectionedResults: SectionedResults<Key, ResultType>!
+        var token: AnyCancellable?
+
         override func updateValue() {
             let realm = try! Realm(configuration: configuration ?? Realm.Configuration.defaultConfiguration)
             var results = realm.objects(ResultType.self)
@@ -659,7 +662,24 @@ extension Projection: _ObservedResultsValue { }
                 sortDescriptors.append(.init(keyPath: keyPathString, ascending: true))
             }
 
-            value = results.sectioned(sortDescriptors: sortDescriptors, sectionBlock)
+            value = results
+
+            /*
+             Observing the sectioned results directly doesn't allow the SwiftUI diff to work
+             correctly as the previous state of the sectioned results will have the new values.
+
+             An example of when this is an issue is when an item is deleted in a List containing sectioned results,
+             the diff needs a stable state of the previous transaction but due to
+             the observation callback calling calculate_sections the collection will be brought up to date.
+
+             The solution around this is to store a frozen copy of the sectioned results and observe the parent `Results` instead.
+             Each time the results observation callback is invoked and the SwiftUI View is redrawn the sectioned results will be updated.
+             */
+            sectionedResults = value.sectioned(sortDescriptors: sortDescriptors, sectionBlock).freeze()
+            token = self.objectWillChange.sink { [weak self] _ in
+                guard let self = self else { return }
+                self.sectionedResults = self.value.sectioned(sortDescriptors: self.sortDescriptors, self.sectionBlock).freeze()
+            }
         }
 
         var sortDescriptors: [SortDescriptor] = [] {
@@ -684,7 +704,7 @@ extension Projection: _ObservedResultsValue { }
             if self.sortDescriptors.isEmpty {
                 throwRealmException("sortDescriptors must not be empty when sectioning ObservedSectionedResults with `sectionBlock`")
             }
-            super.init(value.sectioned(sortDescriptors: self.sortDescriptors, self.sectionBlock), keyPaths)
+            super.init(value, keyPaths)
         }
     }
 
@@ -717,13 +737,25 @@ extension Projection: _ObservedResultsValue { }
     /// :nodoc:
     public var wrappedValue: SectionedResults<Key, ResultType> {
         storage.setupValue()
-        return storage.value
+        return storage.sectionedResults
     }
     /// :nodoc:
     public var projectedValue: Self {
         return self
     }
 
+    /// Removes items from an `@ObservedSectionedResults` collection
+    /// with a given `IndexSet` and `ResultsSection`.
+    /// - Parameters:
+    ///   - offsets: Index offsets in the section.
+    ///   - section: The section containing the items to remove.
+    public func remove(atOffsets offsets: IndexSet,
+                       section: ResultsSection<Key, ResultType>) where ResultType: ObjectBase & ThreadConfined {
+        write(wrappedValue) { collection in
+            collection.realm?.delete(offsets.compactMap { section[$0].thaw() ?? nil })
+        }
+    }
+
     private init(type: ResultType.Type,
                  sectionBlock: @escaping ((ResultType) -> Key),
                  sortDescriptors: [SortDescriptor] = [],

RealmSwift/Tests/SwiftUITests.swift

@@ -735,6 +735,7 @@ class SwiftUITests: TestCase {
             // add another default inited object for filter comparison
             realm.add(object)
         }
+        realm.refresh()
         XCTAssertEqual(fullResults.wrappedValue.count, 1)
         XCTAssertEqual(fullResults.wrappedValue[0].key, "abc")
 
@@ -780,6 +781,7 @@ class SwiftUITests: TestCase {
             // add another default inited object for filter comparison
             realm.add(object)
         }
+        realm.refresh()
         XCTAssertEqual(fullResults.wrappedValue.count, 1)
         XCTAssertEqual(fullResults.wrappedValue[0].key, "abc")