Add ComboBoxAssist.ShowSelectedItem attached property

This attached property add ability to change visibility of selected item
in combobox

Author: l1pton17

MaterialDesignThemes.Wpf/ComboBoxAssist.cs

@@ -0,0 +1,33 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Windows;
+
+namespace MaterialDesignThemes.Wpf
+{
+    public static class ComboBoxAssist
+    {
+        #region ShowSelectedItem
+
+        public static readonly DependencyProperty ShowSelectedItemProperty = DependencyProperty.RegisterAttached(
+            "ShowSelectedItem",
+            typeof (bool),
+            typeof (ComboBoxAssist),
+            new FrameworkPropertyMetadata(false,
+                FrameworkPropertyMetadataOptions.AffectsRender | FrameworkPropertyMetadataOptions.Inherits));
+
+        public static bool GetShowSelectedItem(DependencyObject element, object value)
+        {
+            return (bool)element.GetValue(ShowSelectedItemProperty);
+        }
+
+        public static void SetShowSelectedItem(DependencyObject element, object value)
+        {
+            element.SetValue(ShowSelectedItemProperty, value);
+        }
+
+        #endregion
+    }
+}

MaterialDesignThemes.Wpf/MaterialDesignThemes.Wpf.csproj

@@ -238,6 +238,7 @@
     <Compile Include="ClockItemButton.cs" />
     <Compile Include="ColorZone.cs" />
     <Compile Include="ColorZoneAssist.cs" />
+    <Compile Include="ComboBoxAssist.cs" />
     <Compile Include="ComboBoxPopup.cs" />
     <Compile Include="Converters\BooleanToVisibilityConverter.cs" />
     <Compile Include="Converters\BrushRoundConverter.cs" />

MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.ComboBox.xaml

@@ -554,6 +554,9 @@
             </Trigger>
             <Trigger Property="IsEditable" Value="true">
                 <Setter Property="IsTabStop" Value="false" />
+                <Setter Property="wpf:ComboBoxAssist.ShowSelectedItem" Value="True"/>
+            </Trigger>
+            <Trigger Property="wpf:ComboBoxAssist.ShowSelectedItem" Value="True">
                 <Setter Property="ItemContainerStyle" Value="{StaticResource MaterialDesignComboBoxItemStyle}" />
             </Trigger>
         </Style.Triggers>