Created a new ThemeAssist class that allows for easy overriding of the color themes. (#1036)

Added a new property to the DialogHost for setting the theme color of the dialog. Defaulted the normal dialog host to light to maintain backward compatibility.

Author: Keboo

MaterialDesignThemes.Wpf/BaseTheme.cs

@@ -0,0 +1,9 @@
+namespace MaterialDesignThemes.Wpf
+{
+    public enum BaseTheme
+    {
+        Inherit,
+        Light,
+        Dark
+    }
+}

MaterialDesignThemes.Wpf/DialogHost.cs

@@ -414,6 +414,18 @@ public SnackbarMessageQueue SnackbarMessageQueue
             set { SetValue(SnackbarMessageQueueProperty, value); }
         }
 
+        public static readonly DependencyProperty DialogThemeProperty =
+            DependencyProperty.Register(nameof(DialogTheme), typeof(BaseTheme), typeof(DialogHost), new PropertyMetadata(default(BaseTheme)));
+
+        /// <summary>
+        /// Set the theme (light/dark) for the dialog.
+        /// </summary>
+        public BaseTheme DialogTheme
+        {
+            get { return (BaseTheme)GetValue(DialogThemeProperty); }
+            set { SetValue(DialogThemeProperty, value); }
+        }
+
         public static readonly DependencyProperty PopupStyleProperty = DependencyProperty.Register(
             nameof(PopupStyle), typeof(Style), typeof(DialogHost), new PropertyMetadata(default(Style)));
 

MaterialDesignThemes.Wpf/MaterialDesignThemes.Wpf.csproj

@@ -261,6 +261,7 @@
   </ItemGroup>
   <ItemGroup>
     <Compile Include="Badged.cs" />
+    <Compile Include="BaseTheme.cs" />
     <Compile Include="ButtonProgressAssist.cs" />
     <Compile Include="Card.cs" />
     <Compile Include="Chip.cs" />
@@ -341,6 +342,7 @@
     <Compile Include="SnackbarMessageQueue.cs" />
     <Compile Include="SnackbarMessageQueueItem.cs" />
     <Compile Include="Spelling.cs" />
+    <Compile Include="ThemeAssist.cs" />
     <Compile Include="Transitions\CircleWipe.cs" />
     <Compile Include="IHintProxy.cs" />
     <Compile Include="Transitions\FadeWipe.cs" />

MaterialDesignThemes.Wpf/ThemeAssist.cs

@@ -0,0 +1,58 @@
+using System;
+using System.Windows;
+
+namespace MaterialDesignThemes.Wpf
+{
+    public static class ThemeAssist
+    {
+        public static BaseTheme GetTheme(DependencyObject obj)
+        {
+            return (BaseTheme)obj.GetValue(ThemeProperty);
+        }
+
+        public static void SetTheme(DependencyObject obj, BaseTheme value)
+        {
+            obj.SetValue(ThemeProperty, value);
+        }
+
+        public static readonly DependencyProperty ThemeProperty =
+            DependencyProperty.RegisterAttached("Theme", typeof(BaseTheme), typeof(ThemeAssist), new PropertyMetadata(default(BaseTheme), OnThemeChanged));
+
+        private static void OnThemeChanged(DependencyObject @do, DependencyPropertyChangedEventArgs e)
+        {
+            if (@do is FrameworkElement element)
+            {
+                if (e.OldValue is BaseTheme oldTheme && 
+                    GetResourceDictionarySource(oldTheme) is string oldSource)
+                {
+                    foreach(ResourceDictionary resourceDictionary in element.Resources.MergedDictionaries)
+                    {
+                        if (string.Equals(resourceDictionary.Source.ToString(), oldSource, StringComparison.Ordinal))
+                        {
+                            element.Resources.MergedDictionaries.Remove(resourceDictionary);
+                            break;
+                        }
+                    }
+                }
+
+                if (e.NewValue is BaseTheme newTheme &&
+                    GetResourceDictionarySource(newTheme) is string newThemeSource)
+                {
+                    element.Resources.MergedDictionaries.Add(new ResourceDictionary { Source = new Uri(newThemeSource) });
+                }
+            }
+        }
+
+        private static string GetResourceDictionarySource(BaseTheme theme)
+        {
+            switch (theme)
+            {
+                case BaseTheme.Light:
+                    return "pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesignTheme.Light.xaml";
+                case BaseTheme.Dark:
+                    return "pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesignTheme.Dark.xaml";
+            }
+            return null;
+        }
+    }
+}

MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.DialogHost.xaml

@@ -16,6 +16,7 @@
     <Style TargetType="{x:Type wpf:DialogHost}">
         <Setter Property="DialogMargin" Value="35" />
         <Setter Property="wpf:ShadowAssist.ShadowDepth" Value="Depth5" />
+        <Setter Property="DialogTheme" Value="Light" />
         <Setter Property="PopupStyle" Value="{StaticResource MaterialDesignDialogHostPopup}" />
         <Setter Property="Template">
             <Setter.Value>
@@ -135,15 +136,9 @@
                             </VisualStateGroup>
                         </VisualStateManager.VisualStateGroups>
                         <controlzEx:PopupEx PlacementTarget="{Binding ElementName=DialogHostRoot, Mode=OneWay}"
-                                            x:Name="PART_Popup"
-                                            Style="{TemplateBinding PopupStyle}">
-                            <controlzEx:PopupEx.Resources>
-                                <ResourceDictionary>
-                                    <ResourceDictionary.MergedDictionaries>
-                                        <ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesignTheme.Light.xaml" />
-                                    </ResourceDictionary.MergedDictionaries>
-                                </ResourceDictionary>
-                            </controlzEx:PopupEx.Resources>
+                                            x:Name="PART_Popup" 
+                                            Style="{TemplateBinding PopupStyle}"
+                                            wpf:ThemeAssist.Theme="{TemplateBinding DialogTheme}">
                             <wpf:Card x:Name="PART_PopupContentElement" 
                                         Margin="{TemplateBinding DialogMargin}"
                                         wpf:ShadowAssist.ShadowDepth="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=(wpf:ShadowAssist.ShadowDepth)}"
@@ -319,7 +314,7 @@
 
                         <Grid x:Name="PART_ContentCoverGrid" Background="{x:Null}" Opacity="1" IsHitTestVisible="False" Focusable="False" />
 
-                        <Grid x:Name="PART_Popup" 
+                        <Grid x:Name="PART_Popup" wpf:ThemeAssist.Theme="{TemplateBinding DialogTheme}"
                               HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" 
                               VerticalAlignment="{TemplateBinding VerticalContentAlignment}">
                             <wpf:Card