Add ObservationRegistrar logic

Author: rickclephas

KMPObservableViewModelCore/ObservableProperties.swift

@@ -0,0 +1,62 @@
+//
+//  ObservableProperties.swift
+//  KMPObservableViewModelCore
+//
+//  Created by Rick Clephas on 25/10/2025.
+//
+
+import Observation
+import KMPObservableViewModelCoreObjC
+
+/// Helper object that maps any external `Property` to an `ObservableProperty`.
+@available(iOS 17.0, macOS 14.0, tvOS 17.0, watchOS 10.0, *)
+internal final class ObservableProperties {
+    
+    private var properties: [ObjectIdentifier:ObservableProperty] = [:]
+    
+    private func observableProperty(_ property: any Property) -> ObservableProperty {
+        let identifier = ObjectIdentifier(property)
+        if let observableProperty = properties[identifier] { return observableProperty }
+        let observableProperty = ObservableProperty(property)
+        properties[identifier] = observableProperty
+        return observableProperty
+    }
+    
+    func access(_ property: any Property) {
+        observableProperty(property).access()
+    }
+    
+    func willSet(_ property: any Property) {
+        observableProperty(property).willSet()
+    }
+    
+    func didSet(_ property: any Property) {
+        observableProperty(property).didSet()
+    }
+}
+
+/// Helper object that turns an external `Property` into a Swift observable property.
+@available(iOS 17.0, macOS 14.0, tvOS 17.0, watchOS 10.0, *)
+private final class ObservableProperty: Observable {
+    
+    private let registrar = ObservationRegistrar()
+    private let property: any Property
+    
+    init(_ property: any Property) {
+        self.property = property
+    }
+    
+    var value: Any? { property.value }
+    
+    func access() {
+        registrar.access(self, keyPath: \.value)
+    }
+    
+    func willSet() {
+        registrar.willSet(self, keyPath: \.value)
+    }
+    
+    func didSet() {
+        registrar.didSet(self, keyPath: \.value)
+    }
+}

KMPObservableViewModelCore/ObservableViewModelPublisher.swift

@@ -18,18 +18,43 @@ public final class ObservableViewModelPublisher: Combine.Publisher, KMPObservabl
     private let publisher: ObservableObjectPublisher
     private let subscriptionCount: any SubscriptionCount
 
+    private var _observableProperties: Any? = nil
+    @available(iOS 17.0, macOS 14.0, tvOS 17.0, watchOS 10.0, *)
+    private var observableProperties: ObservableProperties? {
+        _observableProperties as! ObservableProperties?
+    }
+    
     internal init(_ viewModel: any ViewModel) {
         self.publisher = viewModel.objectWillChange
         self.subscriptionCount = viewModel.viewModelScope.subscriptionCount
+        if #available(iOS 17.0, macOS 14.0, tvOS 17.0, watchOS 10.0, *), viewModel is Observable {
+            _observableProperties = ObservableProperties()
+        }
     }
 
     public func receive<S>(subscriber: S) where S : Subscriber, Never == S.Failure, Void == S.Input {
         subscriptionCount.increase()
         publisher.receive(subscriber: ObservableViewModelSubscriber(subscriptionCount, subscriber))
     }
 
-    public func send() {
-        publisher.send()
+    public func access(_ property: any Property) {
+        if #available(iOS 17.0, macOS 14.0, tvOS 17.0, watchOS 10.0, *), let observableProperties {
+            observableProperties.access(property)
+        }
+    }
+    
+    public func willSet(_ property: any Property) {
+        if #available(iOS 17.0, macOS 14.0, tvOS 17.0, watchOS 10.0, *), let observableProperties {
+            observableProperties.willSet(property)
+        } else {
+            publisher.send()
+        }
+    }
+    
+    public func didSet(_ property: any Property) {
+        if #available(iOS 17.0, macOS 14.0, tvOS 17.0, watchOS 10.0, *), let observableProperties {
+            observableProperties.didSet(property)
+        }
     }
 }
 

KMPObservableViewModelCoreObjC/KMPOVMProperty.h

@@ -0,0 +1,22 @@
+//
+//  KMPOVMProperty.h
+//  KMPObservableViewModelCoreObjC
+//
+//  Created by Rick Clephas on 25/10/2025.
+//
+
+#ifndef KMPOVMProperty_h
+#define KMPOVMProperty_h
+
+#import <Foundation/Foundation.h>
+
+NS_ASSUME_NONNULL_BEGIN
+
+__attribute__((swift_name("Property")))
+@protocol KMPOVMProperty
+@property (readonly) id _Nullable value;
+@end
+
+NS_ASSUME_NONNULL_END
+
+#endif /* KMPOVMProperty_h */

KMPObservableViewModelCoreObjC/KMPOVMPublisher.h

@@ -9,12 +9,15 @@
 #define KMPOVMPublisher_h
 
 #import <Foundation/Foundation.h>
+#import "KMPOVMProperty.h"
 
 NS_ASSUME_NONNULL_BEGIN
 
 __attribute__((swift_name("Publisher")))
 @protocol KMPOVMPublisher
-- (void)send;
+- (void)access:(id<KMPOVMProperty>)property;
+- (void)willSet:(id<KMPOVMProperty>)property;
+- (void)didSet:(id<KMPOVMProperty>)property;
 @end
 
 NS_ASSUME_NONNULL_END

KMPObservableViewModelCoreObjC/KMPObservableViewModelCoreObjC.h

@@ -5,6 +5,7 @@
 //  Created by Rick Clephas on 27/11/2022.
 //
 
+#import "KMPOVMProperty.h"
 #import "KMPOVMPublisher.h"
 #import "KMPOVMSubscriptionCount.h"
 #import "KMPOVMViewModelScope.h"

kmp-observableviewmodel-core/src/appleMain/kotlin/com/rickclephas/kmp/observableviewmodel/ObservableStateFlow.kt

@@ -17,13 +17,18 @@ internal class ObservableMutableStateFlow<T>(
     private val stateFlow: MutableStateFlow<T>
 ): MutableStateFlow<T> {
 
+    private val property = StateFlowProperty(stateFlow)
+
     override var value: T
-        get() = stateFlow.value
+        get() {
+            viewModelScope.publisher?.access(property)
+            return stateFlow.value
+        }
         set(value) {
-            if (stateFlow.value != value) {
-                viewModelScope.publisher?.send()
-            }
+            val publisher = viewModelScope.publisher?.takeIf { stateFlow.value != value }
+            publisher?.willSet(property)
             stateFlow.value = value
+            publisher?.didSet(property)
         }
 
     override val replayCache: List<T>
@@ -38,10 +43,11 @@ internal class ObservableMutableStateFlow<T>(
         stateFlow.collect(collector)
 
     override fun compareAndSet(expect: T, update: T): Boolean {
-        if (stateFlow.value == expect && expect != update) {
-            viewModelScope.publisher?.send()
-        }
-        return stateFlow.compareAndSet(expect, update)
+        val publisher = viewModelScope.publisher?.takeIf { stateFlow.value == expect && expect != update }
+        publisher?.willSet(property)
+        val result = stateFlow.compareAndSet(expect, update)
+        publisher?.didSet(property)
+        return result
     }
 
     @ExperimentalCoroutinesApi

kmp-observableviewmodel-core/src/appleMain/kotlin/com/rickclephas/kmp/observableviewmodel/StateFlowProperty.kt

@@ -0,0 +1,14 @@
+package com.rickclephas.kmp.observableviewmodel
+
+import com.rickclephas.kmp.observableviewmodel.objc.KMPOVMPropertyProtocol
+import kotlinx.coroutines.flow.StateFlow
+import platform.darwin.NSObject
+
+/**
+ * A [Property][KMPOVMPropertyProtocol] that retrieves its value from a [StateFlow].
+ */
+internal class StateFlowProperty<out T>(
+    private val stateFlow: StateFlow<T>
+): NSObject(), KMPOVMPropertyProtocol {
+    override fun value(): T = stateFlow.value
+}

kmp-observableviewmodel-core/src/nativeInterop/cinterop/KMPObservableViewModelCoreObjC.def

@@ -1,3 +1,3 @@
 language = Objective-C
 package = com.rickclephas.kmp.observableviewmodel.objc
-headers = KMPOVMPublisher.h KMPOVMSubscriptionCount.h KMPOVMViewModelScope.h
+headers = KMPOVMProperty.h KMPOVMPublisher.h KMPOVMSubscriptionCount.h KMPOVMViewModelScope.h

sample/iosApp/KMPObservableViewModelSample/KMPObservableViewModel.swift

@@ -8,4 +8,6 @@
 import KMPObservableViewModelCore
 import KMPObservableViewModelSampleShared
 
-extension Kmp_observableviewmodel_coreViewModel: ViewModel { }
+extension Kmp_observableviewmodel_coreViewModel: @retroactive ViewModel { }
+
+extension Kmp_observableviewmodel_coreViewModel: @retroactive Observable { }