Store ObservableViewModelPublisher inside NativeViewModelScope

Author: rickclephas

KMPObservableViewModelCore/ObservableViewModel.swift

@@ -13,8 +13,7 @@ import KMPObservableViewModelCoreObjC
 public func observableViewModel<VM: ViewModel>(
     for viewModel: VM
 ) -> ObservableViewModel<VM> {
-    let publishers = observableViewModelPublishers(for: viewModel)
-    return ObservableViewModel(publishers, viewModel)
+    return ObservableViewModel(viewModel)
 }
 
 /// Gets an `ObservableObject` for the specified `ViewModel`.
@@ -35,13 +34,9 @@ public final class ObservableViewModel<VM: ViewModel>: ObservableObject, Hashabl
     /// The observed `ViewModel`.
     public let viewModel: VM
 
-    /// Holds a strong reference to the publishers
-    private let publishers: ObservableViewModelPublishers
-    
-    internal init(_ publishers: ObservableViewModelPublishers, _ viewModel: VM) {
-        objectWillChange = publishers.publisher
+    internal init(_ viewModel: VM) {
+        objectWillChange = viewModel.viewModelWillChange
         self.viewModel = viewModel
-        self.publishers = publishers
     }
 
     public static func == (lhs: ObservableViewModel<VM>, rhs: ObservableViewModel<VM>) -> Bool {

KMPObservableViewModelCore/ObservableViewModelPublisher.swift

@@ -9,32 +9,30 @@ import Combine
 import KMPObservableViewModelCoreObjC
 
 /// Publisher for `ObservableViewModel` that connects to the `ViewModelScope`.
-public final class ObservableViewModelPublisher: Publisher {
+public final class ObservableViewModelPublisher: Combine.Publisher, KMPObservableViewModelCoreObjC.Publisher {
     public typealias Output = Void
     public typealias Failure = Never
 
     internal weak var viewModel: (any ViewModel)?
-    private let subscriptionCount: any SubscriptionCount
 
-    private let publisher = ObservableObjectPublisher()
-    private var objectWillChangeCancellable: AnyCancellable? = nil
+    private let publisher: ObservableObjectPublisher
+    private let subscriptionCount: any SubscriptionCount
 
-    internal init(_ viewModel: any ViewModel, _ objectWillChange: ObservableObjectPublisher) {
+    internal init(_ viewModel: any ViewModel) {
         self.viewModel = viewModel
+        self.publisher = viewModel.objectWillChange
         self.subscriptionCount = viewModel.viewModelScope.subscriptionCount
-        viewModel.viewModelScope.setSendObjectWillChange { [weak self] in
-            self?.publisher.send()
-        }
-        objectWillChangeCancellable = objectWillChange.sink { [weak self] _ in
-            self?.publisher.send()
-        }
     }
 
     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()
+    }
+    
     deinit {
         guard let viewModel else { return }
         if let cancellable = viewModel as? Cancellable {

KMPObservableViewModelCore/ObservableViewModelPublishers.swift

@@ -26,7 +26,7 @@ internal func observableViewModelPublishers<VM: ViewModel>(
             fatalError("ObservableViewModel has been deallocated")
         }()
     } else {
-        let publisher = ObservableViewModelPublisher(viewModel, viewModel.objectWillChange)
+        let publisher = ObservableViewModelPublisher(viewModel)
         publishers = ObservableViewModelPublishers(publisher)
         let object = WeakObservableViewModelPublishers(publishers)
         objc_setAssociatedObject(viewModel, &observableViewModelPublishersKey, object, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)

KMPObservableViewModelCore/ViewModel.swift

@@ -12,7 +12,20 @@ import KMPObservableViewModelCoreObjC
 public protocol ViewModel: ObservableObject where ObjectWillChangePublisher == ObservableObjectPublisher {
     /// The `ViewModelScope` of this `ViewModel`.
     var viewModelScope: ViewModelScope { get }
+    /// An `ObservableViewModelPublisher` that emits before this `ViewModel` has changed.
+    var viewModelWillChange: ObservableViewModelPublisher { get }
     /// Internal KMP-ObservableViewModel function used to clear the ViewModel.
     /// - Warning: You should NOT call this yourself!
     func clear()
 }
+
+public extension ViewModel {
+    var viewModelWillChange: ObservableViewModelPublisher {
+        if let publisher = viewModelScope.publisher {
+            return publisher as! ObservableViewModelPublisher
+        }
+        let publisher = ObservableViewModelPublisher(self)
+        viewModelScope.publisher = publisher
+        return publisher
+    }
+}

KMPObservableViewModelCoreObjC/KMPOVMPublisher.h

@@ -0,0 +1,22 @@
+//
+//  KMPOVMPublisher.h
+//  KMPObservableViewModel
+//
+//  Created by Rick Clephas on 09/06/2025.
+//
+
+#ifndef KMPOVMPublisher_h
+#define KMPOVMPublisher_h
+
+#import <Foundation/Foundation.h>
+
+NS_ASSUME_NONNULL_BEGIN
+
+__attribute__((swift_name("Publisher")))
+@protocol KMPOVMPublisher
+- (void)send;
+@end
+
+NS_ASSUME_NONNULL_END
+
+#endif /* KMPOVMPublisher_h */

KMPObservableViewModelCoreObjC/KMPOVMViewModelScope.h

@@ -9,15 +9,15 @@
 #define KMPOVMViewModelScope_h
 
 #import <Foundation/Foundation.h>
+#import "KMPOVMPublisher.h"
 #import "KMPOVMSubscriptionCount.h"
 
 NS_ASSUME_NONNULL_BEGIN
 
 __attribute__((swift_name("ViewModelScope")))
 @protocol KMPOVMViewModelScope
 @property (readonly) id<KMPOVMSubscriptionCount> subscriptionCount;
-
-- (void)setSendObjectWillChange:(void (^ _Nonnull)(void))sendObjectWillChange;
+@property id<KMPOVMPublisher> _Nullable publisher;
 @end
 
 NS_ASSUME_NONNULL_END

KMPObservableViewModelCoreObjC/KMPObservableViewModelCoreObjC.h

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

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

@@ -1,5 +1,6 @@
 package com.rickclephas.kmp.observableviewmodel
 
+import com.rickclephas.kmp.observableviewmodel.objc.KMPOVMPublisherProtocol
 import kotlinx.coroutines.CoroutineScope
 import platform.darwin.NSObject
 
@@ -14,20 +15,11 @@ internal class NativeViewModelScope internal constructor(
     private val _subscriptionCount = SubscriptionCount()
     override fun subscriptionCount(): SubscriptionCount = _subscriptionCount
 
-    private var sendObjectWillChange: (() -> Unit)? = null
-
-    override fun setSendObjectWillChange(sendObjectWillChange: () -> Unit) {
-        if (this.sendObjectWillChange != null) {
-            throw IllegalStateException("ViewModel can't be wrapped more than once")
-        }
-        this.sendObjectWillChange = sendObjectWillChange
-    }
-
-    /**
-     * Invokes the object will change listener set by [setSendObjectWillChange].
-     */
-    fun sendObjectWillChange() {
-        sendObjectWillChange?.invoke()
+    private var _publisher: KMPOVMPublisherProtocol? = null
+    override fun publisher(): KMPOVMPublisherProtocol? = _publisher
+    override fun setPublisher(publisher: KMPOVMPublisherProtocol?) {
+        if (_publisher != null) throw IllegalStateException("ViewModel can't be initialized more than once")
+        _publisher = publisher
     }
 }
 

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

@@ -8,7 +8,7 @@ import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 
 /**
- * A [MutableStateFlow] that triggers [NativeViewModelScope.sendObjectWillChange]
+ * A [MutableStateFlow] that triggers [NativeViewModelScope.publisher]
  * and accounts for the [NativeViewModelScope.subscriptionCount].
  */
 @OptIn(ExperimentalForInheritanceCoroutinesApi::class)
@@ -21,7 +21,7 @@ internal class ObservableMutableStateFlow<T>(
         get() = stateFlow.value
         set(value) {
             if (stateFlow.value != value) {
-                viewModelScope.sendObjectWillChange()
+                viewModelScope.publisher?.send()
             }
             stateFlow.value = value
         }
@@ -36,7 +36,7 @@ internal class ObservableMutableStateFlow<T>(
 
     override fun compareAndSet(expect: T, update: T): Boolean {
         if (stateFlow.value == expect && expect != update) {
-            viewModelScope.sendObjectWillChange()
+            viewModelScope.publisher?.send()
         }
         return stateFlow.compareAndSet(expect, update)
     }

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

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