Add SelectionBrush and SelectionForegroundBrush Feature

samples/ControlCatalog/Pages/TextBoxPage.xaml

@@ -26,6 +26,9 @@
         <TextBox Width="200" Text="Left aligned text" TextAlignment="Left" />
         <TextBox Width="200" Text="Center aligned text" TextAlignment="Center" />
         <TextBox Width="200" Text="Right aligned text" TextAlignment="Right" />
+         <TextBox Width="200" Text="Custom selection brush"
+                  SelectionStart="5" SelectionEnd="22"
+                  SelectionBrush="Green" SelectionForegroundBrush="Yellow"/>
       </StackPanel>
 
       <StackPanel Orientation="Vertical" Spacing="8">

src/Avalonia.Controls/Presenters/TextPresenter.cs

@@ -19,6 +19,12 @@ namespace Avalonia.Controls.Presenters
         public static readonly StyledProperty<char> PasswordCharProperty =
             AvaloniaProperty.Register<TextPresenter, char>(nameof(PasswordChar));
 
+        public static readonly StyledProperty<IBrush> SelectionBrushProperty =
+           AvaloniaProperty.Register<TextPresenter, IBrush>(nameof(SelectionBrushProperty));
+
+        public static readonly StyledProperty<IBrush> SelectionForegroundBrushProperty =
+        AvaloniaProperty.Register<TextPresenter, IBrush>(nameof(SelectionForegroundBrushProperty));
+
         public static readonly DirectProperty<TextPresenter, int> SelectionStartProperty =
             TextBox.SelectionStartProperty.AddOwner<TextPresenter>(
                 o => o.SelectionStart,
@@ -34,7 +40,7 @@ namespace Avalonia.Controls.Presenters
         private int _selectionStart;
         private int _selectionEnd;
         private bool _caretBlink;
-        private IBrush _highlightBrush;
+        private IBrush _selectionBrush;
         
         static TextPresenter()
         {
@@ -79,6 +85,18 @@ namespace Avalonia.Controls.Presenters
             set => SetValue(PasswordCharProperty, value);
         }
 
+        public IBrush SelectionBrush
+        {
+            get => GetValue(SelectionBrushProperty);
+            set => SetValue(SelectionBrushProperty, value);
+        }
+
+        public IBrush SelectionForegroundBrush
+        {
+            get => GetValue(SelectionForegroundBrushProperty);
+            set => SetValue(SelectionForegroundBrushProperty, value);
+        }
+
         public int SelectionStart
         {
             get
@@ -129,14 +147,11 @@ namespace Avalonia.Controls.Presenters
 
                 var rects = FormattedText.HitTestTextRange(start, length);
 
-                if (_highlightBrush == null)
-                {
-                    _highlightBrush = (IBrush)this.FindResource("HighlightBrush");
-                }
+                _selectionBrush = SelectionBrush;
 
                 foreach (var rect in rects)
                 {
-                    context.FillRectangle(_highlightBrush, rect);
+                    context.FillRectangle(_selectionBrush, rect);
                 }
             }
 
@@ -247,12 +262,13 @@ namespace Avalonia.Controls.Presenters
             var selectionEnd = SelectionEnd;
             var start = Math.Min(selectionStart, selectionEnd);
             var length = Math.Max(selectionStart, selectionEnd) - start;
+            var selectionForegroundBrush = SelectionForegroundBrush ?? Brushes.White;
 
             if (length > 0)
             {
                 result.Spans = new[]
                 {
-                    new FormattedTextStyleSpan(start, length, foregroundBrush: Brushes.White),
+                    new FormattedTextStyleSpan(start, length, foregroundBrush: selectionForegroundBrush),
                 };
             }
 

src/Avalonia.Controls/TextBox.cs

@@ -38,6 +38,12 @@ namespace Avalonia.Controls
         public static readonly StyledProperty<char> PasswordCharProperty =
             AvaloniaProperty.Register<TextBox, char>(nameof(PasswordChar));
 
+        public static readonly StyledProperty<IBrush> SelectionBrushProperty =
+           AvaloniaProperty.Register<TextBox, IBrush>(nameof(SelectionBrushProperty));
+
+        public static readonly StyledProperty<IBrush> SelectionForegroundBrushProperty =
+        AvaloniaProperty.Register<TextBox, IBrush>(nameof(SelectionForegroundBrushProperty));
+
         public static readonly DirectProperty<TextBox, int> SelectionStartProperty =
             AvaloniaProperty.RegisterDirect<TextBox, int>(
                 nameof(SelectionStart),
@@ -169,6 +175,18 @@ namespace Avalonia.Controls
             set => SetValue(PasswordCharProperty, value);
         }
 
+        public IBrush SelectionBrush
+        {
+            get => GetValue(SelectionBrushProperty);
+            set => SetValue(SelectionBrushProperty, value);
+        }
+
+        public IBrush SelectionForegroundBrush
+        {
+            get => GetValue(SelectionForegroundBrushProperty);
+            set => SetValue(SelectionForegroundBrushProperty, value);
+        }
+
         public int SelectionStart
         {
             get
@@ -456,7 +474,7 @@ namespace Avalonia.Controls
                 movement = true;
                 selection = false;
                 handled = true;
-                
+
             }
             else if (Match(keymap.MoveCursorToTheEndOfLine))
             {
@@ -485,7 +503,7 @@ namespace Avalonia.Controls
                 movement = true;
                 selection = true;
                 handled = true;
-                
+
             }
             else if (Match(keymap.MoveCursorToTheEndOfLineWithSelection))
             {

src/Avalonia.Themes.Default/TextBox.xaml

@@ -3,6 +3,7 @@
     <Setter Property="Background" Value="{DynamicResource ThemeBackgroundBrush}"/>
     <Setter Property="BorderBrush" Value="{DynamicResource ThemeBorderMidBrush}"/>
     <Setter Property="BorderThickness" Value="{DynamicResource ThemeBorderThickness}"/>
+    <Setter Property="SelectionBrush" Value="{DynamicResource HighlightBrush}"/>
     <Setter Property="Padding" Value="4"/>
     <Setter Property="Template">
       <ControlTemplate>
@@ -44,7 +45,9 @@
                                  SelectionEnd="{TemplateBinding SelectionEnd}"
                                  TextAlignment="{TemplateBinding TextAlignment}"
                                  TextWrapping="{TemplateBinding TextWrapping}"
-                                 PasswordChar="{TemplateBinding PasswordChar}"/>
+                                 PasswordChar="{TemplateBinding PasswordChar}"
+                                 SelectionBrush="{TemplateBinding SelectionBrush}"
+                                 SelectionForegroundBrush="{TemplateBinding SelectionForegroundBrush}"/>
                 </Panel>
               </ScrollViewer>
             </DataValidationErrors>