From af83673f918373f904f91b7abc43c683669602ea Mon Sep 17 00:00:00 2001
From: Andrey Kunchev <donandren@gmail.com>
Date: Thu, 7 Feb 2019 16:46:59 +0200
Subject: [PATCH 1/2] make DropDown support mouse wheel

---
 src/Avalonia.Controls/DropDown.cs | 53 ++++++++++++++++++++++++++++++-
 1 file changed, 52 insertions(+), 1 deletion(-)

diff --git a/src/Avalonia.Controls/DropDown.cs b/src/Avalonia.Controls/DropDown.cs
index 93b33e0589..684279a3cd 100644
--- a/src/Avalonia.Controls/DropDown.cs
+++ b/src/Avalonia.Controls/DropDown.cs
@@ -56,6 +56,7 @@ namespace Avalonia.Controls
         private bool _isDropDownOpen;
         private Popup _popup;
         private object _selectionBoxItem;
+        private IDisposable _subscriptionsOnOpen;
 
         /// <summary>
         /// Initializes static members of the <see cref="DropDown"/> class.
@@ -174,6 +175,37 @@ namespace Avalonia.Controls
             }
         }
 
+        /// <inheritdoc/>
+        protected override void OnPointerWheelChanged(PointerWheelEventArgs e)
+        {
+            base.OnPointerWheelChanged(e);
+
+            if (!e.Handled)
+            {
+                if (!IsDropDownOpen)
+                {
+                    if (IsFocused)
+                    {
+                        if (e.Delta.Y < 0)
+                        {
+                            if (++SelectedIndex >= ItemCount)
+                                SelectedIndex = 0;
+                        }
+                        else
+                        {
+                            if (--SelectedIndex < 0)
+                                SelectedIndex = ItemCount - 1;
+                        }
+                        e.Handled = true;
+                    }
+                }
+                else
+                {
+                    e.Handled = true;
+                }
+            }
+        }
+
         /// <inheritdoc/>
         protected override void OnPointerPressed(PointerPressedEventArgs e)
         {
@@ -223,6 +255,9 @@ namespace Avalonia.Controls
 
         private void PopupClosed(object sender, EventArgs e)
         {
+            _subscriptionsOnOpen?.Dispose();
+            _subscriptionsOnOpen = null;
+
             if (CanFocus(this))
             {
                 Focus();
@@ -232,6 +267,22 @@ namespace Avalonia.Controls
         private void PopupOpened(object sender, EventArgs e)
         {
             TryFocusSelectedItem();
+
+            _subscriptionsOnOpen?.Dispose();
+            _subscriptionsOnOpen = null;
+
+            var toplevel = this.GetVisualRoot() as TopLevel;
+            if (toplevel != null)
+            {
+                _subscriptionsOnOpen = toplevel.AddHandler(PointerWheelChangedEvent, (s, ev) =>
+                {
+                    //eat wheel scroll event outside dropdown popup while it's open
+                    if (IsDropDownOpen && (ev.Source as IVisual).GetVisualRoot() == toplevel)
+                    {
+                        ev.Handled = true;
+                    }
+                }, Interactivity.RoutingStrategies.Tunnel);
+            }
         }
 
         private void SelectedItemChanged(AvaloniaPropertyChangedEventArgs e)
@@ -247,7 +298,7 @@ namespace Avalonia.Controls
             {
                 var container = ItemContainerGenerator.ContainerFromIndex(selectedIndex);
 
-                if(container == null && SelectedItems.Count > 0)
+                if (container == null && SelectedItems.Count > 0)
                 {
                     ScrollIntoView(SelectedItems[0]);
                     container = ItemContainerGenerator.ContainerFromIndex(selectedIndex);

From f285c38d2766368767f2fee844743fd7365af821 Mon Sep 17 00:00:00 2001
From: Andrey Kunchev <donandren@gmail.com>
Date: Thu, 7 Feb 2019 17:22:56 +0200
Subject: [PATCH 2/2] improve dropdown key up/down and mouse wheel auto
 selections so they don't go through unselected state

---
 src/Avalonia.Controls/DropDown.cs | 39 ++++++++++++++++++++-----------
 1 file changed, 25 insertions(+), 14 deletions(-)

diff --git a/src/Avalonia.Controls/DropDown.cs b/src/Avalonia.Controls/DropDown.cs
index 684279a3cd..4f65a0aed4 100644
--- a/src/Avalonia.Controls/DropDown.cs
+++ b/src/Avalonia.Controls/DropDown.cs
@@ -150,16 +150,12 @@ namespace Avalonia.Controls
             {
                 if (e.Key == Key.Down)
                 {
-                    if (++SelectedIndex >= ItemCount)
-                        SelectedIndex = 0;
-
+                    SelectNext();
                     e.Handled = true;
                 }
                 else if (e.Key == Key.Up)
                 {
-                    if (--SelectedIndex < 0)
-                        SelectedIndex = ItemCount - 1;
-
+                    SelectPrev();
                     e.Handled = true;
                 }
             }
@@ -187,15 +183,10 @@ namespace Avalonia.Controls
                     if (IsFocused)
                     {
                         if (e.Delta.Y < 0)
-                        {
-                            if (++SelectedIndex >= ItemCount)
-                                SelectedIndex = 0;
-                        }
+                            SelectNext();
                         else
-                        {
-                            if (--SelectedIndex < 0)
-                                SelectedIndex = ItemCount - 1;
-                        }
+                            SelectPrev();
+
                         e.Handled = true;
                     }
                 }
@@ -358,5 +349,25 @@ namespace Avalonia.Controls
                 }
             }
         }
+
+        private void SelectNext()
+        {
+            int next = SelectedIndex + 1;
+
+            if (next >= ItemCount)
+                next = 0;
+
+            SelectedIndex = next;
+        }
+
+        private void SelectPrev()
+        {
+            int prev = SelectedIndex - 1;
+
+            if (prev < 0)
+                prev = ItemCount - 1;
+
+            SelectedIndex = prev;
+        }
     }
 }