From 817476ef77401cf42980147def0aa0067f658647 Mon Sep 17 00:00:00 2001
From: Dan Walmsley <dan@walms.co.uk>
Date: Fri, 29 May 2020 13:31:03 -0300
Subject: [PATCH] implement a pressed mixin.

---
 src/Avalonia.Controls/Mixins/PressedMixin.cs  | 33 +++++++++++++++++
 .../Mixins/PressedMixinTests.cs               | 37 +++++++++++++++++++
 2 files changed, 70 insertions(+)
 create mode 100644 src/Avalonia.Controls/Mixins/PressedMixin.cs
 create mode 100644 tests/Avalonia.Controls.UnitTests/Mixins/PressedMixinTests.cs

diff --git a/src/Avalonia.Controls/Mixins/PressedMixin.cs b/src/Avalonia.Controls/Mixins/PressedMixin.cs
new file mode 100644
index 0000000000..01b0a8564f
--- /dev/null
+++ b/src/Avalonia.Controls/Mixins/PressedMixin.cs
@@ -0,0 +1,33 @@
+using Avalonia.Interactivity;
+using Avalonia.Input;
+
+namespace Avalonia.Controls.Mixins
+{
+    /// <summary>
+    /// Adds pressed functionality to control classes.
+    /// 
+    /// Adds the ':pressed' class when the item is pressed.
+    /// </summary>
+    public static class PressedMixin
+    {
+        private static void HandlePointerPressed<TControl>(TControl sender, PointerPressedEventArgs e) where TControl : Control
+        {
+            if (e.GetCurrentPoint(sender).Properties.IsLeftButtonPressed)
+            {
+                ((IPseudoClasses)sender.Classes).Set(":pressed", true);
+            }
+        }
+
+        private static void HandlePointerReleased<TControl>(TControl sender) where TControl : Control
+        {
+            ((IPseudoClasses)sender.Classes).Set(":pressed", false);
+        }
+
+        public static void Attach<TControl>() where TControl : Control
+        {
+            InputElement.PointerPressedEvent.AddClassHandler<TControl>((x, e) => HandlePointerPressed(x, e), RoutingStrategies.Tunnel, true);
+            InputElement.PointerReleasedEvent.AddClassHandler<TControl>((x, e) => HandlePointerReleased(x), RoutingStrategies.Tunnel, true);
+            InputElement.PointerCaptureLostEvent.AddClassHandler<TControl>((x, e) => HandlePointerReleased(x), RoutingStrategies.Tunnel, true);
+        }
+    }
+}
diff --git a/tests/Avalonia.Controls.UnitTests/Mixins/PressedMixinTests.cs b/tests/Avalonia.Controls.UnitTests/Mixins/PressedMixinTests.cs
new file mode 100644
index 0000000000..0ff1f40121
--- /dev/null
+++ b/tests/Avalonia.Controls.UnitTests/Mixins/PressedMixinTests.cs
@@ -0,0 +1,37 @@
+using Avalonia.Controls.Mixins;
+using Avalonia.UnitTests;
+using Xunit;
+
+namespace Avalonia.Controls.UnitTests.Mixins
+{
+    public class PressedMixinTests
+    {
+        private MouseTestHelper _mouse = new MouseTestHelper();
+
+        [Fact]
+        public void Selected_Class_Should_Not_Initially_Be_Added()
+        {
+            var target = new TestControl();
+
+            Assert.Empty(target.Classes);
+        }
+
+        [Fact]
+        public void Setting_IsSelected_Should_Add_Selected_Class()
+        {
+            var target = new TestControl();
+
+            _mouse.Down(target);
+
+            Assert.Equal(new[] { ":pressed" }, target.Classes);
+        }
+
+        private class TestControl : Control
+        {
+            static TestControl()
+            {
+                PressedMixin.Attach<TestControl>();
+            }
+        }
+    }
+}