Remove tags from style activators.

They're no longer needed.

src/Avalonia.Base/Styling/Activators/AndActivator.cs

@@ -20,7 +20,7 @@ namespace Avalonia.Styling.Activators
             _sources.Add(activator);
         }
 
-        void IStyleActivatorSink.OnNext(bool value, int tag) => ReevaluateIsActive();
+        void IStyleActivatorSink.OnNext(bool value) => ReevaluateIsActive();
 
         protected override bool EvaluateIsActive()
         {
@@ -44,11 +44,9 @@ namespace Avalonia.Styling.Activators
         {
             if (_sources is object)
             {
-                var i = 0;
-
                 foreach (var source in _sources)
                 {
-                    source.Subscribe(this, i++);
+                    source.Subscribe(this);
                 }
             }
         }

src/Avalonia.Base/Styling/Activators/IStyleActivator.cs

@@ -9,11 +9,11 @@ namespace Avalonia.Styling.Activators
     /// <remarks>
     /// A style activator is very similar to an `IObservable{bool}` but is optimized for the
     /// particular use-case of activating a style according to a selector. It differs from
-    /// an observable in two major ways:
+    /// an observable in three major ways:
     /// 
     /// - Can only have a single subscription
-    /// - The subscription can have a tag associated with it, allowing a subscriber to index
+    /// - The activation state can be re-evaluated at any time by calling <see cref="GetIsActive"/>
-    ///   into a list of subscriptions without having to allocate additional objects.
+    /// - No error or completion messages
     /// </remarks>
     [Unstable]
     public interface IStyleActivator : IDisposable
@@ -38,11 +38,10 @@ namespace Avalonia.Styling.Activators
         /// Subscribes to the activator.
         /// </summary>
         /// <param name="sink">The listener.</param>
-        /// <param name="tag">An optional tag.</param>
         /// <remarks>
         /// This method should not call <see cref="IStyleActivatorSink.OnNext(bool, int)"/>.
         /// </remarks>
-        void Subscribe(IStyleActivatorSink sink, int tag = 0);
+        void Subscribe(IStyleActivatorSink sink);
 
         /// <summary>
         /// Unsubscribes from the activator.

src/Avalonia.Base/Styling/Activators/IStyleActivatorSink.cs

@@ -12,7 +12,6 @@ namespace Avalonia.Styling.Activators
         /// Called when the subscribed activator value changes.
         /// </summary>
         /// <param name="value">The new value.</param>
-        /// <param name="tag">The subscription tag.</param>
+        void OnNext(bool value);
-        void OnNext(bool value, int tag);
     }
 }

src/Avalonia.Base/Styling/Activators/NotActivator.cs

@@ -7,9 +7,9 @@
     {
         private readonly IStyleActivator _source;
         public NotActivator(IStyleActivator source) => _source = source;
-        void IStyleActivatorSink.OnNext(bool value, int tag) => ReevaluateIsActive();
+        void IStyleActivatorSink.OnNext(bool value) => ReevaluateIsActive();
         protected override bool EvaluateIsActive() => !_source.GetIsActive();
-        protected override void Initialize() => _source.Subscribe(this, 0);
+        protected override void Initialize() => _source.Subscribe(this);
         protected override void Deinitialize() => _source.Unsubscribe(this);
     }
 }

src/Avalonia.Base/Styling/Activators/OrActivator.cs

@@ -18,7 +18,7 @@ namespace Avalonia.Styling.Activators
             _sources.Add(activator);
         }
 
-        void IStyleActivatorSink.OnNext(bool value, int tag) => ReevaluateIsActive();
+        void IStyleActivatorSink.OnNext(bool value) => ReevaluateIsActive();
 
         protected override bool EvaluateIsActive()
         {
@@ -38,11 +38,9 @@ namespace Avalonia.Styling.Activators
         {
             if (_sources is object)
             {
-                var i = 0;
-
                 foreach (var source in _sources)
                 {
-                    source.Subscribe(this, i++);
+                    source.Subscribe(this);
                 }
             }
         }

src/Avalonia.Base/Styling/Activators/StyleActivatorBase.cs

@@ -6,20 +6,18 @@ namespace Avalonia.Styling.Activators
     internal abstract class StyleActivatorBase : IStyleActivator
     {
         private IStyleActivatorSink? _sink;
-        private int _tag;
         private bool _value;
 
         public bool GetIsActive() => _value = EvaluateIsActive();
 
         public bool IsSubscribed => _sink is not null;
 
-        public void Subscribe(IStyleActivatorSink sink, int tag = 0)
+        public void Subscribe(IStyleActivatorSink sink)
         {
             if (_sink is null)
             {
                 Initialize();
                 _sink = sink;
-                _tag = tag;
             }
             else
             {
@@ -70,14 +68,14 @@ namespace Avalonia.Styling.Activators
             if (value != _value)
             {
                 _value = value;
-                _sink?.OnNext(value, _tag);
+                _sink?.OnNext(value);
             }
 
             return value;
         }
 
         /// <summary>
-        /// Called in response to a <see cref="Subscribe(IStyleActivatorSink, int)"/> to allow the
+        /// Called in response to a <see cref="Subscribe(IStyleActivatorSink)"/> to allow the
         /// derived class to set up any necessary subscriptions.
         /// </summary>
         protected abstract void Initialize();

src/Avalonia.Base/Styling/StyleInstance.cs

@@ -79,7 +79,7 @@ namespace Avalonia.Styling
 
         public new void MakeShared() => base.MakeShared();
 
-        void IStyleActivatorSink.OnNext(bool value, int tag)
+        void IStyleActivatorSink.OnNext(bool value)
         {
             Owner?.OnFrameActivationChanged(this);
             _animationTrigger?.OnNext(value);

tests/Avalonia.Base.UnitTests/Styling/SelectorTests_Nesting.cs

@@ -300,7 +300,7 @@ namespace Avalonia.Base.UnitTests.Styling
 
 
             public bool Active { get; private set; }
-            public void OnNext(bool value, int tag) => Active = value;
+            public void OnNext(bool value) => Active = value;
         }
     }
 }

tests/Avalonia.Base.UnitTests/Styling/StyleActivatorExtensions.cs

@@ -42,7 +42,7 @@ namespace Avalonia.Base.UnitTests.Styling
                 observer.OnNext(_source.GetIsActive());
             }
 
-            void IStyleActivatorSink.OnNext(bool value, int tag)
+            void IStyleActivatorSink.OnNext(bool value)
             {
                 PublishNext(value);
             }