From 7d1bba782532e6f788abf2f76699f9e3dac409a9 Mon Sep 17 00:00:00 2001
From: robloo <robloo@users.noreply.github.com>
Date: Thu, 25 Aug 2022 20:53:20 -0400
Subject: [PATCH] Add DoNothingForNullConverter to fix color palette binding

---
 .../Converters/DoNothingForNullConverter.cs   | 35 +++++++++++++++++++
 .../Themes/Fluent/ColorView.xaml              |  3 +-
 2 files changed, 37 insertions(+), 1 deletion(-)
 create mode 100644 src/Avalonia.Controls.ColorPicker/Converters/DoNothingForNullConverter.cs

diff --git a/src/Avalonia.Controls.ColorPicker/Converters/DoNothingForNullConverter.cs b/src/Avalonia.Controls.ColorPicker/Converters/DoNothingForNullConverter.cs
new file mode 100644
index 0000000000..421a5acb28
--- /dev/null
+++ b/src/Avalonia.Controls.ColorPicker/Converters/DoNothingForNullConverter.cs
@@ -0,0 +1,35 @@
+using System;
+using System.Globalization;
+using Avalonia.Data;
+using Avalonia.Data.Converters;
+
+namespace Avalonia.Controls.Converters
+{
+    /// <summary>
+    /// Converter that will do nothing (not update bound values) when a null value is encountered.
+    /// This converter enables binding nullable with non-nullable properties in some scenarios.
+    /// </summary>
+    public class DoNothingForNullConverter : IValueConverter
+    {
+        /// <inheritdoc/>
+        public object? Convert(
+            object? value,
+            Type targetType,
+            object? parameter,
+            CultureInfo culture)
+        {
+            return value ?? BindingOperations.DoNothing;
+        }
+
+        /// <inheritdoc/>
+        public object? ConvertBack(
+            object? value,
+            Type targetType,
+            object? parameter,
+            CultureInfo culture)
+        {
+            return value ?? BindingOperations.DoNothing;
+        }
+    }
+}
+
diff --git a/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorView.xaml b/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorView.xaml
index 59cc48975f..dab4142001 100644
--- a/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorView.xaml
+++ b/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorView.xaml
@@ -11,6 +11,7 @@
   <pc:ThirdComponentConverter x:Key="ThirdComponentConverter" />
   <converters:ColorToDisplayNameConverter x:Key="ColorToDisplayNameConverter" />
   <converters:ColorToHexConverter x:Key="ColorToHexConverter" />
+  <converters:DoNothingForNullConverter x:Key="DoNothingForNullConverter" />
   <globalization:NumberFormatInfo x:Key="ColorViewComponentNumberFormat" NumberDecimalDigits="0" />
   <x:Double x:Key="ColorViewTabStripHeight">48</x:Double>
   <x:Double x:Key="ColorViewComponentLabelWidth">30</x:Double>
@@ -205,7 +206,7 @@
                 </Border>
               </TabItem.Header>
               <ListBox Items="{TemplateBinding PaletteColors}"
-                       SelectedItem="{Binding Color, RelativeSource={RelativeSource TemplatedParent}, Mode=TwoWay}"
+                       SelectedItem="{Binding Color, RelativeSource={RelativeSource TemplatedParent}, Converter={StaticResource DoNothingForNullConverter}, Mode=TwoWay}"
                        UseLayoutRounding="False"
                        Margin="12">
                 <ListBox.Styles>