From 6e26cd58fa6d7324484a4766da03b2bdc1c91eb7 Mon Sep 17 00:00:00 2001
From: ReeJK <wnezros@gmail.com>
Date: Tue, 13 Apr 2021 13:37:04 +0300
Subject: [PATCH] Button state update when CommandParameter changed

---
 src/Avalonia.Controls/Button.cs               | 13 ++++++++
 .../ButtonTests.cs                            | 33 +++++++++++++++----
 2 files changed, 40 insertions(+), 6 deletions(-)

diff --git a/src/Avalonia.Controls/Button.cs b/src/Avalonia.Controls/Button.cs
index 6093cbd581..6ebbfd05f6 100644
--- a/src/Avalonia.Controls/Button.cs
+++ b/src/Avalonia.Controls/Button.cs
@@ -89,6 +89,7 @@ namespace Avalonia.Controls
         {
             FocusableProperty.OverrideDefaultValue(typeof(Button), true);
             CommandProperty.Changed.Subscribe(CommandChanged);
+            CommandParameterProperty.Changed.Subscribe(CommandParameterChanged);
             IsDefaultProperty.Changed.Subscribe(IsDefaultChanged);
             IsCancelProperty.Changed.Subscribe(IsCancelChanged);
         }
@@ -380,6 +381,18 @@ namespace Avalonia.Controls
             }
         }
 
+        /// <summary>
+        /// Called when the <see cref="CommandParameter"/> property changes.
+        /// </summary>
+        /// <param name="e">The event args.</param>
+        private static void CommandParameterChanged(AvaloniaPropertyChangedEventArgs e)
+        {
+            if (e.Sender is Button button)
+            {
+                button.CanExecuteChanged(button, EventArgs.Empty);
+            }
+        }
+
         /// <summary>
         /// Called when the <see cref="IsDefault"/> property changes.
         /// </summary>
diff --git a/tests/Avalonia.Controls.UnitTests/ButtonTests.cs b/tests/Avalonia.Controls.UnitTests/ButtonTests.cs
index 7ad0e480c6..c9ad24e654 100644
--- a/tests/Avalonia.Controls.UnitTests/ButtonTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/ButtonTests.cs
@@ -269,6 +269,19 @@ namespace Avalonia.Controls.UnitTests
             Assert.Equal(0, command.SubscriptionCount);
         }
 
+        [Fact]
+        public void Button_Invokes_CanExecute_When_CommandParameter_Changed()
+        {
+            var command = new TestCommand(p => p is bool value && value);
+            var target = new Button { Command = command };
+
+            target.CommandParameter = true;
+            Assert.True(target.IsEffectivelyEnabled);
+
+            target.CommandParameter = false;
+            Assert.False(target.IsEffectivelyEnabled);
+        }
+
         private class TestButton : Button, IRenderRoot
         {
             public TestButton()
@@ -324,12 +337,22 @@ namespace Avalonia.Controls.UnitTests
 
         private class TestCommand : ICommand
         {
+            private readonly Func<object, bool> _canExecute;
+            private readonly Action<object> _execute;
             private EventHandler _canExecuteChanged;
-            private bool _enabled;
+            private bool _enabled = true;
 
-            public TestCommand(bool enabled)
+            public TestCommand(bool enabled = true)
             {
                 _enabled = enabled;
+                _canExecute = _ => _enabled;
+                _execute = _ => { };
+            }
+
+            public TestCommand(Func<object, bool> canExecute, Action<object> execute = null)
+            {
+                _canExecute = canExecute;
+                _execute = execute ?? (_ => { });
             }
 
             public bool IsEnabled
@@ -353,11 +376,9 @@ namespace Avalonia.Controls.UnitTests
                 remove { _canExecuteChanged -= value; --SubscriptionCount; }
             }
 
-            public bool CanExecute(object parameter) => _enabled;
+            public bool CanExecute(object parameter) => _canExecute(parameter);
 
-            public void Execute(object parameter)
-            {
-            }
+            public void Execute(object parameter) => _execute(parameter);
         }
     }
 }