[C] Lowest specificity for propagated values (#17648)

IsEnabled value is propagated on parenting. Do this with the special
(fromHandler) specificity, to allow styling

- fixes #17597

src/Controls/src/Core/BindableObject.cs

@@ -124,19 +124,29 @@ namespace Microsoft.Maui.Controls
 			if (bpcontext == null)
 				return;
 
-			var original = bpcontext.Values.GetSpecificityAndValue().Value;
-			var newValue = bpcontext.Values.GetClearedValue();
-			var changed = !Equals(original, newValue);
+			var original = bpcontext.Values.GetSpecificityAndValue();
+			if (original.Key == SetterSpecificity.FromHandler)			
+				bpcontext.Values.Remove(SetterSpecificity.FromHandler);
+			
+
+			var newValue = bpcontext.Values.GetClearedValue(specificity);
+			var changed = !Equals(original.Value, newValue);
 			if (changed)
 			{
-				property.PropertyChanging?.Invoke(this, original, newValue);
+				property.PropertyChanging?.Invoke(this, original.Value, newValue);
 				OnPropertyChanging(property.PropertyName);
 			}
+
 			bpcontext.Values.Remove(specificity);
+
+			//there's some side effect implemented in CoerceValue (see IsEnabled) that we need to trigger here
+			if (property.CoerceValue != null)
+				property.CoerceValue(this, newValue);
+
 			if (changed)
 			{
 				OnPropertyChanged(property.PropertyName);
-				property.PropertyChanged?.Invoke(this, original, newValue);
+				property.PropertyChanged?.Invoke(this, original.Value, newValue);
 			}
 		}
 

src/Controls/src/Core/BindableObjectExtensions.cs

@@ -23,7 +23,7 @@ namespace Microsoft.Maui.Controls
 			else
 			{
 				// support normal/code properties
-				self.SetValue(property, value);
+				self.SetValue(property, value, SetterSpecificity.FromHandler);
 			}
 		}
 

src/Controls/src/Core/SetterSpecificityList.cs

@@ -91,26 +91,24 @@ namespace Microsoft.Maui.Controls
 		}
 
 		/// <summary>
-		/// Called by ClearValueCore, returns what the value would be if cleared
+		/// Called by ClearValueCore, returns what the top value would be if cleared
 		/// </summary>
-		public object? GetClearedValue()
+		public object? GetClearedValue(SetterSpecificity clearedSpecificity)
 		{
 			if (_values is not null)
 			{
-				return _values.Count >= 2 ? _values[_values.Keys[_values.Count - 2]] : null;
+				var index = _values.IndexOfKey(clearedSpecificity);
+				if (index == _values.Count -1) //last value will be cleared
+					return _values.Count >= 2 ? _values[_values.Keys[_values.Count - 2]] : null;
+				return _values.Last().Value;
 			}
 
 			// Fast path should return the "lower" value
 			if (_first is not null && _second is not null)
 			{
-				if (_second.Value.Key.CompareTo(_first.Value.Key) >= 0)
-				{
-					return _first.Value.Value;
-				}
-				else
-				{
+				if (_first.Value.Key == clearedSpecificity)
 					return _second.Value.Value;
-				}
+				return _first.Value.Value;				
 			}
 			else if (_first is not null)
 			{

src/Controls/tests/Core.UnitTests/SetterSpecificityListTests.cs

@@ -63,9 +63,10 @@ namespace Microsoft.Maui.Controls.Core.UnitTests
 		{
 			var list = new SetterSpecificityList();
 			list.SetValue(SetterSpecificity.DefaultValue, nameof(SetterSpecificity.DefaultValue));
-			Assert.Equal(nameof(SetterSpecificity.DefaultValue), list.GetClearedValue());
+			Assert.Equal(nameof(SetterSpecificity.DefaultValue), list.GetClearedValue(SetterSpecificity.DefaultValue));
 			list.SetValue(SetterSpecificity.ManualValueSetter, nameof(SetterSpecificity.ManualValueSetter));
-			Assert.Equal(nameof(SetterSpecificity.DefaultValue), list.GetClearedValue());
+			Assert.Equal(nameof(SetterSpecificity.DefaultValue), list.GetClearedValue(SetterSpecificity.ManualValueSetter));
 		}
 	}
 }
+ 

src/Controls/tests/Xaml.UnitTests/Issues/Maui17597.xaml

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             xmlns:local="clr-namespace:Microsoft.Maui.Controls.Xaml.UnitTests"
+             x:Class="Microsoft.Maui.Controls.Xaml.UnitTests.Maui17597">
+    <StackLayout>
+         <Entry x:Name="Test_Entry" Text="Remove Text To Disable Button"/>
+         <Button x:Name="button" Text="Test Button" Margin="0,10,0,0" >
+             <Button.Style>
+                 <Style TargetType="Button">
+                     <Setter Property="IsEnabled" Value="True"/> <!-- Does not seem to honor this statement at all -->
+                     <Style.Triggers>                          
+                         <DataTrigger Binding="{Binding Source={x:Reference Test_Entry}, Path=Text.Length}" TargetType="Button"  Value="0">
+                             <Setter Property="IsEnabled" Value="False" />
+                         </DataTrigger>
+                     </Style.Triggers>
+                 </Style>
+             </Button.Style>
+         </Button>
+     </StackLayout> 
+</ContentPage>

src/Controls/tests/Xaml.UnitTests/Issues/Maui17597.xaml.cs

@@ -0,0 +1,55 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
+using Microsoft.Maui.ApplicationModel;
+using Microsoft.Maui.Controls.Core.UnitTests;
+using Microsoft.Maui.Controls.Shapes;
+using Microsoft.Maui.Devices;
+using Microsoft.Maui.Graphics;
+using Microsoft.Maui.UnitTests;
+using Microsoft.Maui.Dispatching;
+using NUnit.Framework;
+
+namespace Microsoft.Maui.Controls.Xaml.UnitTests;
+
+public partial class Maui17597 : ContentPage
+{
+
+	public Maui17597() => InitializeComponent();
+
+	public Maui17597(bool useCompiledXaml)
+	{
+		//this stub will be replaced at compile time
+	}
+
+	[TestFixture]
+	class Test
+	{
+		[SetUp]
+		public void Setup()
+		{
+			Application.SetCurrentApplication(new MockApplication());
+			DispatcherProvider.SetCurrent(new DispatcherProviderStub());
+		}
+
+
+		[TearDown] public void TearDown() => AppInfo.SetCurrent(null);
+		[Test]
+		public void DataTriggerInStyle([Values(false, true)] bool useCompiledXaml)
+		{
+			var page = new Maui17597(useCompiledXaml);
+			Assert.That(page.Test_Entry.Text, Is.EqualTo("Remove Text To Disable Button"));
+			Assert.That(page.button.IsEnabled, Is.True);
+
+			page.Test_Entry.SetValueFromRenderer(Entry.TextProperty, "");
+			Assert.That(page.Test_Entry.Text, Is.Empty);
+			Assert.That(page.Test_Entry.Text.Length, Is.EqualTo(0));
+			Assert.That(page.button.IsEnabled, Is.False);
+
+			page.Test_Entry.SetValueFromRenderer(Entry.TextProperty, "foo");
+			Assert.That(page.Test_Entry.Text, Is.Not.Empty);
+			Assert.That(page.button.IsEnabled, Is.True);
+		}
+	}
+}