wpf - Combobox background not being applied in windows 8

Question

I am a little confused with wpf themes. I would like to have the wpf screens look the same on Vista, Windows 7 and Windows 8. So I have styled the components accordingly and they don't pose problems except when run on Windows 8. For example I have a combobox and I am changing its default background in xaml like this.

<Style TargetType="{x:Type ComboBox}" >
    <Setter Property="FontStyle" Value="Normal"/>
    <Setter Property="Height" Value="24" />
    <Setter Property="Background" Value="{StaticResource GradientButtonBackgroundBrush}"/>
</Style>

The combobox Background property has no effect in windows 8 and all I get is a flat rectangle with a arrow on right (the default windows 8 combobox, which is rather poorly designed!).

So, my question is that how do I get the combobox look the same on all version of windows. I tried adding windows Aero theme in my App.xaml like below, but it has no effect on the combobox display. Here is how I added Aero theme

<Application.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="/PresentationFramework.Aero;component/themes/aero.normalcolor.xaml"/>
        </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>

There is also another doubt regarding themes. I am building the wpf application on a windows 7 machine, which by default (I believe) has Aero Theme set. So, all my styles are based on the Aero theme when viewed on Windows 7 machine. What happens if I run the application on say XP. Then do I need to add an entry for the resource dictionary (Aero theme) in App.xaml as listed in code above?

I know my question is a bit vague, but believe me, I am really confused with default themes of wpf on different Windows versions.

EDIT: I still can't get combobox to style according to my needs. The combobox still appears like a gray rectangle.

Here is what I did. I downloaded the Aero.NormalColor.xaml from microsoft's site and included in themes folder of application. Then I added the following in App.xaml

    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="/Themes/Aero.NormalColor.xaml"/>
        </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>

Then I Compiled the application and deployed on Windows 8. Still the same combobox as was shown previously. Note that all other elements get styled properly according to the theme. I did the same with Luna.Metallic.xaml and every element gets styled except the ComboBox.

I believe that when I load a particular theme, which defines styles with ControlTemplate, then it should be picked by wpf. I am confused as to why only the ComboBox even after giving it a Aero (or Luna) Control Template doesn't change its appearance. Any ideas ?

EDIT-2 Screen shot of combobox appearance on Windows 8

Answer 1

Well the ComboBox clickable area is actually a ToggleButton

and if you look at the Style for that ToggleButton in Windows-8, you see something like:

<ControlTemplate TargetType="{x:Type ToggleButton}">
  <Border x:Name="templateRoot"
          Background="{StaticResource ComboBox.Static.Background}"
          BorderBrush="{StaticResource ComboBox.Static.Border}"
          BorderThickness="{TemplateBinding BorderThickness}"
          SnapsToDevicePixels="true">
...

As you can see from above, Background used is not a {TemplateBinding Background} but {StaticResource ComboBox.Static.Background}. Hence why you see no effect when you set the Background property in Windows-8 for that ComboBox

If your looking to carry a Style across the different OS Versions(Without having to backtrack and keep checking if new versions screwed up your over-rides), simple rule is Create it yourself.

Create a Style and set it to be applied by TargetType and without a Key to get applied automatically. That way in any OS it's your Style that gets used and not the default underlying one.

This thus guarantees your code run's as you expect on every single OS. Base your Style on the default's of any OS and tweak it to your heart's content.

side-note:

From a usability POV giving the user a Windows-7 ComboBox in an app that run's on Windows-8 is not very nice(unless your entire app looks like a Windows-7 app which is even worse). Your expecting the user to get used to your app's Style's and forget what he's used to from every other app he uses in his OS that use default Styles based on OS. If you have specific reasons for doing so, go ahead but do consider the implications.

Just for example you stated the Windows-8 Style is something your not a fan of, well I'm the opposite. I actually do like the Windows-8 clean and simple look. No distractions to the UserExperience with flashing gradients and things that throw you off the content your putting in front of them. This is an argument that goes on forever. Just be warned abt what the end-user expects and thinks than just what you think is good while writing your program.

Update:

Firstly comment on the relevant answer please. Your answer and your comment update has no relation.

Ok and as for your question edit, what you tried has not worked in windows-8 because PresentationFramework.Aero.dll does not exist in Windows-8 which is what holds Aero.NormalColor.xaml. In Windows-8 your options are PresentationFramework.Aero2.dll which is default and PresentationFramework.AeroLite.dll which I think is used by Windows Server 2012(Not Sure)

Try to compile your program on Windows-8 and you'll see it does not even want to compile.

You'll have to explicitly add a reference to PresentationFramework.Aero and also PresentationUI(which i think is part of .net3) to your project.

Then you'll have to edit your Aero.NormalColor.xaml to something like:

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:theme="clr-namespace:Microsoft.Windows.Themes;assembly=PresentationFramework.Aero"
                    xmlns:ui="clr-namespace:System.Windows.Documents;assembly=PresentationUI">
...

^^ we explicitly state the assembly for Aero Theme. I don't use Windows-7 so Am not sure if that's all that's needed. but you can give that a try.

Try to compile your code in Windows-8 to make sure it will work fine on Windows-8