Move IBinding to BindingBase and tidy up some binding APIs

.ncrunch/Avalonia.Diagnostics.net6.0.v3.ncrunchproject

@@ -0,0 +1,5 @@
+<ProjectConfiguration>
+  <Settings>
+    <IgnoreThisComponentCompletely>True</IgnoreThisComponentCompletely>
+  </Settings>
+</ProjectConfiguration>

.ncrunch/Avalonia.Diagnostics.net8.0.v3.ncrunchproject

@@ -0,0 +1,5 @@
+<ProjectConfiguration>
+  <Settings>
+    <IgnoreThisComponentCompletely>True</IgnoreThisComponentCompletely>
+  </Settings>
+</ProjectConfiguration>

.ncrunch/Avalonia.Diagnostics.netstandard2.0.v3.ncrunchproject

@@ -0,0 +1,5 @@
+<ProjectConfiguration>
+  <Settings>
+    <IgnoreThisComponentCompletely>True</IgnoreThisComponentCompletely>
+  </Settings>
+</ProjectConfiguration>

src/Avalonia.Base/Animation/AnimatorKeyFrame.cs

@@ -46,7 +46,7 @@ public IDisposable BindSetter(IAnimationSetter setter, Animatable targetControl)
             Property = setter.Property;
             var value = setter.Value;
 
-            if (value is IBinding binding)
+            if (value is BindingBase binding)
             {
                 return Bind(ValueProperty, binding, targetControl);
             }

src/Avalonia.Base/AvaloniaObject.cs

@@ -98,7 +98,7 @@ public object? this[AvaloniaProperty property]
         /// Gets or sets a binding for a <see cref="AvaloniaProperty"/>.
         /// </summary>
         /// <param name="binding">The binding information.</param>
-        public IBinding this[IndexerDescriptor binding]
+        public BindingBase this[IndexerDescriptor binding]
         {
             get { return new IndexerBinding(this, binding.Property!, binding.Mode); }
             set { this.Bind(binding.Property!, value); }
@@ -417,14 +417,14 @@ public void SetCurrentValue<T>(StyledProperty<T> property, T value)
         }
 
         /// <summary>
-        /// Binds a <see cref="AvaloniaProperty"/> to an <see cref="IBinding"/>.
+        /// Binds a <see cref="AvaloniaProperty"/> to an <see cref="BindingBase"/>.
         /// </summary>
         /// <param name="property">The property.</param>
         /// <param name="binding">The binding.</param>
         /// <returns>
         /// The binding expression which represents the binding instance on this object.
         /// </returns>
-        public BindingExpressionBase Bind(AvaloniaProperty property, IBinding binding)
+        public BindingExpressionBase Bind(AvaloniaProperty property, BindingBase binding)
         {
             return Bind(property, binding, null);
         }
@@ -474,9 +474,9 @@ public IDisposable Bind<T>(
             VerifyAccess();
             ValidatePriority(priority);
 
-            if (source is IBinding2 b)
+            if (source is BindingBase b)
             {
-                if (b.Instance(this, property, null) is not UntypedBindingExpressionBase expression)
+                if (b.CreateInstance(this, property, null) is not UntypedBindingExpressionBase expression)
                     throw new NotSupportedException($"Binding returned unsupported {nameof(BindingExpressionBase)}.");
 
                 if (priority != expression.Priority)
@@ -574,9 +574,9 @@ public IDisposable Bind<T>(
                 throw new ArgumentException($"The property {property.Name} is readonly.");
             }
 
-            if (source is IBinding2 b)
+            if (source is BindingBase b)
             {
-                if (b.Instance(this, property, null) is not UntypedBindingExpressionBase expression)
+                if (b.CreateInstance(this, property, null) is not UntypedBindingExpressionBase expression)
                     throw new NotSupportedException($"Binding returned unsupported {nameof(BindingExpressionBase)}.");
                 return GetValueStore().AddBinding(property, expression);
             }
@@ -643,7 +643,7 @@ public IDisposable Bind<T>(
         public void CoerceValue(AvaloniaProperty property) => _values.CoerceValue(property);
 
         /// <summary>
-        /// Binds a <see cref="AvaloniaProperty"/> to an <see cref="IBinding"/>.
+        /// Binds a <see cref="AvaloniaProperty"/> to an <see cref="BindingBase"/>.
         /// </summary>
         /// <param name="property">The property.</param>
         /// <param name="binding">The binding.</param>
@@ -656,11 +656,9 @@ public IDisposable Bind<T>(
         /// <returns>
         /// The binding expression which represents the binding instance on this object.
         /// </returns>
-        internal BindingExpressionBase Bind(AvaloniaProperty property, IBinding binding, object? anchor)
+        internal BindingExpressionBase Bind(AvaloniaProperty property, BindingBase binding, object? anchor)
         {
-            if (binding is not IBinding2 b)
-                throw new NotSupportedException($"Unsupported IBinding implementation '{binding}'.");
-            if (b.Instance(this, property, anchor) is not UntypedBindingExpressionBase expression)
+            if (binding.CreateInstance(this, property, anchor) is not UntypedBindingExpressionBase expression)
                 throw new NotSupportedException($"Binding returned unsupported {nameof(BindingExpressionBase)}.");
 
             return GetValueStore().AddBinding(property, expression);

src/Avalonia.Base/AvaloniaObjectExtensions.cs

@@ -11,12 +11,12 @@ namespace Avalonia
     public static class AvaloniaObjectExtensions
     {
         /// <summary>
-        /// Converts an <see cref="IObservable{T}"/> to an <see cref="IBinding"/>.
+        /// Converts an <see cref="IObservable{T}"/> to an <see cref="BindingBase"/>.
         /// </summary>
         /// <typeparam name="T">The type produced by the observable.</typeparam>
         /// <param name="source">The observable</param>
-        /// <returns>An <see cref="IBinding"/>.</returns>
-        public static IBinding ToBinding<T>(this IObservable<T> source)
+        /// <returns>An <see cref="BindingBase"/>.</returns>
+        public static BindingBase ToBinding<T>(this IObservable<T> source)
         {
             return new BindingAdaptor(
                 typeof(T).IsValueType
@@ -228,7 +228,7 @@ public static IDisposable Bind<T>(
         }
 
         /// <summary>
-        /// Binds a property on an <see cref="AvaloniaObject"/> to an <see cref="IBinding"/>.
+        /// Binds a property on an <see cref="AvaloniaObject"/> to an <see cref="BindingBase"/>.
         /// </summary>
         /// <param name="target">The object.</param>
         /// <param name="property">The property to bind.</param>
@@ -244,7 +244,7 @@ public static IDisposable Bind<T>(
         public static IDisposable Bind(
             this AvaloniaObject target,
             AvaloniaProperty property,
-            IBinding binding,
+            BindingBase binding,
             object? anchor = null)
         {
             target = target ?? throw new ArgumentNullException(nameof(target));
@@ -359,7 +359,7 @@ public static IDisposable AddClassHandler<TTarget, TValue>(
             return observable.Subscribe(new ClassHandlerObserver<TTarget, TValue>(action));
         }
 
-        private class BindingAdaptor : IBinding2
+        private class BindingAdaptor : BindingBase
         {
             private readonly IObservable<object?> _source;
 
@@ -368,17 +368,10 @@ public BindingAdaptor(IObservable<object?> source)
                 this._source = source;
             }
 
-            public InstancedBinding? Initiate(
+            internal override BindingExpressionBase CreateInstance(
                 AvaloniaObject target,
-                AvaloniaProperty? targetProperty,
-                object? anchor = null,
-                bool enableDataValidation = false)
-            {
-                var expression = new UntypedObservableBindingExpression(_source, BindingPriority.LocalValue);
-                return new InstancedBinding(expression, BindingMode.OneWay, BindingPriority.LocalValue);
-            }
-
-            BindingExpressionBase IBinding2.Instance(AvaloniaObject target, AvaloniaProperty? property, object? anchor)
+                AvaloniaProperty? property,
+                object? anchor)
             {
                 return new UntypedObservableBindingExpression(_source, BindingPriority.LocalValue);
             }

src/Avalonia.Base/ClassBindingManager.cs

@@ -12,7 +12,7 @@ internal static class ClassBindingManager
         private static readonly Dictionary<string, AvaloniaProperty> s_RegisteredProperties =
             new Dictionary<string, AvaloniaProperty>();
 
-        public static IDisposable Bind(StyledElement target, string className, IBinding source, object anchor)
+        public static IDisposable Bind(StyledElement target, string className, BindingBase source, object anchor)
         {
             var prop = GetClassProperty(className);
             return target.Bind(prop, source);

src/Avalonia.Base/Data/BindingBase.cs

@@ -0,0 +1,28 @@
+namespace Avalonia.Data;
+
+/// <summary>
+/// Base class for the various types of binding supported by Avalonia.
+/// </summary>
+public abstract class BindingBase
+{
+    /// <summary>
+    /// Creates a <see cref="BindingExpressionBase"/> from a binding.
+    /// </summary>
+    /// <param name="target">The target of the binding.</param>
+    /// <param name="targetProperty">The target property of the binding.</param>
+    /// <param name="anchor">
+    /// If <paramref name="target"/> is not a control, provides an anchor object from which to
+    /// locate a data context or other controls.
+    /// </param>
+    /// <returns>
+    /// A newly instantiated <see cref="BindingExpressionBase"/>.
+    /// </returns>
+    /// <remarks>
+    /// This is a low-level method which returns a binding expression that is not yet connected to
+    /// a binding sink, and so is inactive.
+    /// </remarks>
+    internal abstract BindingExpressionBase CreateInstance(
+        AvaloniaObject target,
+        AvaloniaProperty? targetProperty,
+        object? anchor);
+}

src/Avalonia.Base/Data/BindingExpressionBase.cs

@@ -10,8 +10,6 @@ private protected BindingExpressionBase()
     {
     }
 
-    internal BindingMode Mode { get; private protected set; }
-
     public virtual void Dispose()
     {
         GC.SuppressFinalize(this);

src/Avalonia.Base/Data/BindingOperations.cs

@@ -1,106 +1,11 @@
 using System;
-using Avalonia.Diagnostics;
-using Avalonia.Reactive;
 
 namespace Avalonia.Data
 {
     public static class BindingOperations
     {
         public static readonly object DoNothing = new DoNothingType();
 
-        /// <summary>
-        /// Applies an <see cref="InstancedBinding"/> a property on an <see cref="AvaloniaObject"/>.
-        /// </summary>
-        /// <param name="target">The target object.</param>
-        /// <param name="property">The property to bind.</param>
-        /// <param name="binding">The instanced binding.</param>
-        /// <returns>An <see cref="IDisposable"/> which can be used to cancel the binding.</returns>
-        [Obsolete(ObsoletionMessages.MayBeRemovedInAvalonia12)]
-        public static IDisposable Apply(
-            AvaloniaObject target,
-            AvaloniaProperty property,
-            InstancedBinding binding)
-        {
-            _ = target ?? throw new ArgumentNullException(nameof(target));
-            _ = property ?? throw new ArgumentNullException(nameof(property));
-            _ = binding ?? throw new ArgumentNullException(nameof(binding));
-
-            if (binding.Expression is { } expression)
-            {
-                return target.GetValueStore().AddBinding(property, expression);
-            }
-
-            var mode = binding.Mode;
-
-            if (mode == BindingMode.Default)
-            {
-                mode = property.GetMetadata(target).DefaultBindingMode;
-            }
-
-            switch (mode)
-            {
-                case BindingMode.Default:
-                case BindingMode.OneWay:
-                    return target.Bind(property, binding.Source, binding.Priority);
-                case BindingMode.TwoWay:
-                {
-                    if (binding.Source is not IObserver<object?> observer)
-                        throw new InvalidOperationException("InstancedBinding does not contain a subject.");
-                    return new TwoWayBindingDisposable(
-                        target.Bind(property, binding.Source, binding.Priority),
-                        target.GetObservable(property).Subscribe(observer));
-                }
-                case BindingMode.OneTime:
-                {
-                    // Perf: Avoid allocating closure in the outer scope.
-                    var targetCopy = target;
-                    var propertyCopy = property;
-                    var bindingCopy = binding;
-
-                    return binding.Source
-                        .Where(x => BindingNotification.ExtractValue(x) != AvaloniaProperty.UnsetValue)
-                        .Take(1)
-                        .Subscribe(x => targetCopy.SetValue(
-                            propertyCopy,
-                            BindingNotification.ExtractValue(x),
-                            bindingCopy.Priority));
-                }
-
-                case BindingMode.OneWayToSource:
-                {
-                    if (binding.Source is not IObserver<object?> observer)
-                        throw new InvalidOperationException("InstancedBinding does not contain a subject.");
-
-                    return Observable.CombineLatest(
-                        binding.Source,
-                        target.GetObservable(property),
-                        (_, v) => v)
-                    .Subscribe(x => observer.OnNext(x));
-                }
-
-                default:
-                    throw new ArgumentException("Invalid binding mode.");
-            }
-        }
-
-        /// <summary>
-        /// Applies an <see cref="InstancedBinding"/> a property on an <see cref="AvaloniaObject"/>.
-        /// </summary>
-        /// <param name="target">The target object.</param>
-        /// <param name="property">The property to bind.</param>
-        /// <param name="binding">The instanced binding.</param>
-        /// <param name="anchor">Obsolete, unused.</param>
-        /// <returns>An <see cref="IDisposable"/> which can be used to cancel the binding.</returns>
-        [Obsolete("Use the Apply(AvaloniaObject, AvaloniaProperty, InstancedBinding) overload.")]
-        public static IDisposable Apply(
-            AvaloniaObject target,
-            AvaloniaProperty property,
-            InstancedBinding binding,
-            object? anchor)
-        {
-            return Apply(target, property, binding);
-        }
-
         /// <summary>
         /// Retrieves the <see cref="BindingExpressionBase"/> that is currently active on the
         /// specified property.
@@ -119,33 +24,6 @@ public static IDisposable Apply(
         {
             return target.GetValueStore().GetExpression(property);
         }
-
-        private sealed class TwoWayBindingDisposable : IDisposable
-        {
-            private readonly IDisposable _toTargetSubscription;
-            private readonly IDisposable _fromTargetSubsription;
-
-            private bool _isDisposed;
-
-            public TwoWayBindingDisposable(IDisposable toTargetSubscription, IDisposable fromTargetSubsription)
-            {
-                _toTargetSubscription = toTargetSubscription;
-                _fromTargetSubsription = fromTargetSubsription;
-            }
-
-            public void Dispose()
-            {
-                if (_isDisposed)
-                {
-                    return;
-                }
-
-                _fromTargetSubsription.Dispose();
-                _toTargetSubscription.Dispose();
-
-                _isDisposed = true;
-            }
-        }
     }
 
     public sealed class DoNothingType

src/Avalonia.Base/Data/Core/BindingExpression.cs

@@ -23,7 +23,7 @@ namespace Avalonia.Data.Core;
 /// A <see cref="BindingExpression"/> represents a untyped binding which has been
 /// instantiated on an object.
 /// </remarks>
-internal partial class BindingExpression : UntypedBindingExpressionBase, IDescription, IDisposable
+internal class BindingExpression : UntypedBindingExpressionBase, IDescription, IDisposable
 {
     private static readonly List<ExpressionNode> s_emptyExpressionNodes = new();
     private readonly WeakReference<object?>? _source;