Solve SwiftUI performance issues

Realm/Tests/SwiftUISyncTestHostUITests/SwiftUISyncTestHostUITests.swift

@@ -354,6 +354,11 @@ extension SwiftUISyncTestHostUITests {
             realm2.add(SwiftPerson(firstName: "Jane2", lastName: "Doe"))
         }
         user2.waitForUpload(toFinish: partitionValue)
+
+        user1.waitForDownload(toFinish: partitionValue)
+        realm.refresh()
+        XCTAssertEqual(realm.objects(SwiftPerson.self).count, 4)
+
         XCTAssertEqual(table.cells.count, 4)
 
         loginUser(.first)

Realm/Tests/SwiftUITestHost/Objects.swift

@@ -44,5 +44,6 @@ class Reminder: EmbeddedObject, ObjectKeyIdentifiable {
 class ReminderList: Object, ObjectKeyIdentifiable {
     @Persisted var name = "New List"
     @Persisted var icon = "list.bullet"
+    @Persisted var colorNumber: Int = 0
     @Persisted var reminders = RealmSwift.List<Reminder>()
 }

Realm/Tests/SwiftUITestHost/SwiftUITestHostApp.swift

@@ -18,6 +18,7 @@
 
 import RealmSwift
 import SwiftUI
+import Realm.Private
 
 struct ReminderFormView: View {
     @ObservedRealmObject var reminder: Reminder
@@ -306,6 +307,27 @@ struct ObservedResultsSearchableTestView: View {
     }
 }
 
+struct ObservedResultsSchemaBumpTestView: View {
+    @ObservedResults(ReminderList.self) var reminders
+    @State var searchFilter: String = ""
+
+    var body: some View {
+        NavigationView {
+            List {
+                ForEach(reminders) { reminder in
+                    Text(reminder.name)
+                }
+            }
+            .navigationTitle("Reminders")
+            .navigationBarItems(trailing:
+                Button("add") {
+                    let reminder = ReminderList()
+                    $reminders.append(reminder)
+                }.accessibility(identifier: "addList"))
+        }
+    }
+}
+
 @main
 struct App: SwiftUI.App {
     var body: some Scene {
@@ -330,6 +352,10 @@ struct App: SwiftUI.App {
                 } else {
                     return AnyView(EmptyView())
                 }
+            case "schema_bump_test":
+                let newconfiguration = configuration
+                return AnyView(ObservedResultsSchemaBumpTestView()
+                                .environment(\.realmConfiguration, newconfiguration))
             default:
                 return AnyView(ContentView())
             }
@@ -338,4 +364,39 @@ struct App: SwiftUI.App {
             view
         }
     }
+
+    // we are retrieving different configurations for different schema version to been able to test schema migrations on SwiftUI injecting the configuration as an environment value
+    var configuration: Realm.Configuration {
+        let schemaVersion = UInt64(ProcessInfo.processInfo.environment["schema_version"]!)!
+        let rlmConfiguration = RLMRealmConfiguration()
+        rlmConfiguration.objectClasses = [ReminderList.self, Reminder.self]
+        switch schemaVersion {
+        case 2:
+            let schema = RLMSchema(objectClasses: [ReminderList.classForCoder(), Reminder.classForCoder()])
+            let objectSchema = schema.objectSchema[0]
+            let property = objectSchema.properties[2]
+            property.name = "colorFloat"
+            property.type = .float
+            rlmConfiguration.customSchema = schema;
+        default: break
+        }
+
+        // Set the default configuration so we can get a swift configuration with the schema change to force a migration block
+        RLMRealmConfiguration.setDefault(rlmConfiguration)
+        var configuration = Realm.Configuration.defaultConfiguration
+        configuration.schemaVersion = schemaVersion
+        configuration.migrationBlock = { migration, oldSchemaVersion in
+            if oldSchemaVersion < 2 {
+                migration.enumerateObjects(ofType: ReminderList.className()) { oldObject, newObject in
+                    let number = oldObject!["colorNumber"] as? Int ?? 0
+                    newObject!["colorFloat"] = Float(number)
+                }
+            }
+        }
+        configuration.fileURL = URL(string: ProcessInfo.processInfo.environment["schema_bump_path"]!)!
+
+        // Reset the default configuration, so ObservedResults set a clean RLMRealmConfiguration the first time, before injecting the environment configuration
+        RLMRealmConfiguration.setDefault(RLMRealmConfiguration.init())
+        return configuration
+    }
 }

Realm/Tests/SwiftUITestHostUITests/SwiftUITestHostUITests.swift

@@ -288,4 +288,26 @@ class SwiftUITests: XCTestCase {
         searchBar.typeText("12")
         XCTAssertEqual(table.cells.count, 1)
     }
+
+    // This test allow us to test database migrations on a SwiftUI context
+    func testObservedResultsSchemaBump() {
+        let realmPath = URL(string: "\(FileManager.default.temporaryDirectory)\(UUID())")!
+        app.launchEnvironment["schema_bump_path"] = realmPath.absoluteString
+        app.launchEnvironment["test_type"] = "schema_bump_test"
+        app.launchEnvironment["schema_version"] = "1"
+        app.launch()
+
+        let addButton = app.buttons["addList"]
+        (1...5).forEach { _ in
+            addButton.tap()
+        }
+
+        XCTAssertEqual(app.tables.firstMatch.cells.count, 5)
+        app.terminate()
+
+        // We bump the schema version and relaunch the app, which should migrate data from the previous version to the current one
+        app.launchEnvironment["schema_version"] = "2"
+        app.launch()
+        XCTAssertEqual(app.tables.firstMatch.cells.count, 5)
+    }
 }

RealmSwift/Combine.swift

@@ -703,14 +703,16 @@ extension RealmKeyedCollection {
 /// A subscription which wraps a Realm notification.
 @available(OSX 10.15, watchOS 6.0, iOS 13.0, iOSApplicationExtension 13.0, OSXApplicationExtension 10.15, tvOS 13.0, *)
 @frozen public struct ObservationSubscription: Subscription {
-    private var token: NotificationToken
+    private var token: NotificationToken?
     internal init(token: NotificationToken) {
         self.token = token
     }
 
+    internal init() {}
+
     /// A unique identifier for identifying publisher streams.
     public var combineIdentifier: CombineIdentifier {
-        return CombineIdentifier(token)
+        return token != nil ? CombineIdentifier(token!) : CombineIdentifier(NSNumber(value: 0))
     }
 
     /// This function is not implemented.
@@ -721,7 +723,7 @@ extension RealmKeyedCollection {
 
     /// Stop emitting values on this subscription.
     public func cancel() {
-        token.invalidate()
+        token?.invalidate()
     }
 }
 

RealmSwift/SwiftUI.swift

@@ -207,7 +207,7 @@ private final class ObservableStoragePublisher<ObjectType>: Publisher where Obje
         if value.realm != nil && !value.isInvalidated, let value = value.thaw() {
             // This path is for cases where the object is already managed. If an
             // unmanaged object becomes managed it will continue to use KVO.
-            let token =  value._observe(keyPaths, subscriber)
+            let token = value._observe(keyPaths, subscriber)
             subscriber.receive(subscription: ObservationSubscription(token: token))
         } else if let value = unwrappedValue, !value.isInvalidated {
             // else if the value is unmanaged
@@ -222,6 +222,9 @@ private final class ObservableStoragePublisher<ObjectType>: Publisher where Obje
             let subscription = SwiftUIKVO.Subscription(observer: kvo, value: value, keyPaths: keyPaths)
             subscriber.receive(subscription: subscription)
             SwiftUIKVO.observedObjects[value] = subscription
+        } else {
+            // As SwiftUI calls this method before we setup the value, we create an empty subscription which will trigger an UI update when `send` gets called, which will call call again this method and allow us to observe the updated value.
+            subscriber.receive(subscription: ObservationSubscription())
         }
     }
 }
@@ -231,10 +234,8 @@ private class ObservableStorage<ObservedType>: ObservableObject where ObservedTy
     @Published var value: ObservedType {
         willSet {
             if newValue != value {
-                objectWillChange.subscribers.forEach {
-                    $0.receive(subscription: ObservationSubscription(token: newValue._observe(keyPaths, $0)))
-                }
                 objectWillChange.send()
+                self.objectWillChange = ObservableStoragePublisher(newValue, keyPaths)
             }
         }
     }
@@ -405,14 +406,12 @@ extension Projection: _ObservedResultsValue { }
 ///
 /// Given `@ObservedResults var v` in SwiftUI, `$v` refers to a `BoundCollection`.
 ///
-@available(iOS 13.0, macOS 10.15, tvOS 13.0, watchOS 6.0, *)
+@available(iOS 13.0, macOS 11.0, tvOS 13.0, watchOS 6.0, *)
 @propertyWrapper public struct ObservedResults<ResultType>: DynamicProperty, BoundCollection where ResultType: _ObservedResultsValue & RealmFetchable & KeypathSortable & Identifiable {
     private class Storage: ObservableStorage<Results<ResultType>> {
         var setupHasRun = false
         private func didSet() {
-            if setupHasRun {
-                setupValue()
-            }
+            setupValue()
         }
 
         func setupValue() {
@@ -453,6 +452,28 @@ extension Projection: _ObservedResultsValue { }
         }
 
         var searchString: String = ""
+
+        init(_ results: Results<ResultType>,
+             configuration: Realm.Configuration? = nil,
+             filter: NSPredicate? = nil,
+             keyPaths: [String]? = nil,
+             sortDescriptor: SortDescriptor? = nil) where ResultType: Object {
+            super.init(results, keyPaths)
+            self.configuration = configuration
+            self.filter = filter
+            self.sortDescriptor = sortDescriptor
+        }
+
+        init<ObjectType: ObjectBase>(_ results: Results<ResultType>,
+                                     configuration: Realm.Configuration? = nil,
+                                     filter: NSPredicate? = nil,
+                                     keyPaths: [String]? = nil,
+                                     sortDescriptor: SortDescriptor? = nil) where ResultType: Projection<ObjectType>, ObjectType: ThreadConfined {
+            super.init(results, keyPaths)
+            self.configuration = configuration
+            self.filter = filter
+            self.sortDescriptor = sortDescriptor
+        }
     }
 
     @Environment(\.realmConfiguration) var configuration
@@ -524,10 +545,10 @@ extension Projection: _ObservedResultsValue { }
                                         keyPaths: [String]? = nil,
                                         sortDescriptor: SortDescriptor? = nil) where ResultType: Projection<ObjectType>, ObjectType: ThreadConfined {
         let results = Results<ResultType>(RLMResults<ResultType>.emptyDetached())
-        self.storage = Storage(results, keyPaths)
-        self.storage.configuration = configuration
-        self.filter = filter
-        self.sortDescriptor = sortDescriptor
+        self.storage = Storage(results,
+                               configuration: configuration,
+                               filter: filter,
+                               sortDescriptor: sortDescriptor)
     }
     /**
      Initialize a `ObservedResults` struct for a given `Object` or `EmbeddedObject` type.
@@ -547,10 +568,11 @@ extension Projection: _ObservedResultsValue { }
                 filter: NSPredicate? = nil,
                 keyPaths: [String]? = nil,
                 sortDescriptor: SortDescriptor? = nil) where ResultType: Object {
-        self.storage = Storage(Results(RLMResults<ResultType>.emptyDetached()), keyPaths)
-        self.storage.configuration = configuration
-        self.filter = filter
-        self.sortDescriptor = sortDescriptor
+        let results = Results<ResultType>(RLMResults<ResultType>.emptyDetached())
+        self.storage = Storage(results,
+                               configuration: configuration,
+                               filter: filter,
+                               sortDescriptor: sortDescriptor)
     }
 #if swift(>=5.5)
     /**