Windows 7 WPF style on Windows XP / 8 / 8.1

The issue

If you have a few years experience, than you already faced with the issue probably: WPF style looks different on different Windows'. You develop and design something on Windows 7, but some old-fashion customer still have Windows XP or maybe already installed the brand new Windows 8.1 and everything falls apart. You can prevent it when you use your own style, custom controls and redefine every single style property. Well, it does not sound too friendly. But don't worry, there is another option.

Why is it different in the first place?

Although the .NET runtime framework has the same version, somehow it still looks different on different OSs due the default style on Windows XP is Luna, on Windows 7 is Aero (first introduced in Vista) and on Windows 8 / 8.1 is Aero2 (or Aero Glass). If you create a WPF application and don't change the theme, references or create custom styles then one of those themes will be applied respectively to the OS Version.
On one hand it is a little bit annoying, since one does not want to create a complete custom style for an intern-used-only application just to make sure progressbars and comoboxes as well as word wrapping  are the same. On the other hand it has to be this way to make sure OS design is consistent. So, whenever your application is gonna need the PresentationFramework.dll, the current OS will provide it's own default.

Solution

The solution is easier than you think. You don't need to customize any control or use 3rd party stuff. All you need is to tell your app to use e.g the Aero theme. First copy the Windows 7 Aero DLLs (PresentationCore.dll, PresentationFramework.dll, PresentationFramework.Aero.dll) to your solution folder from c:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.0\ and then explicit reference them into your solution. After that, modify your App.xaml and include the theme as resource. Enjoy :)

<Application x:Class="WPFAeroDemo.App"

             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

             StartupUri="MainWindow.xaml">

    <Application.Resources>

        <ResourceDictionary>

            <ResourceDictionary.MergedDictionaries>

                <ResourceDictionary Source="/PresentationFramework.Aero;component/themes/Aero.NormalColor.xaml"/>

            </ResourceDictionary.MergedDictionaries>

        </ResourceDictionary>

    </Application.Resources>

</Application>

Result

Without explicit theme definition

OS Default style on Windows XP (left), on Windows 7 (middle) and on Windows 8.1 (right)

With explicit definition

Aero style on Windows XP (left), on Windows 7 (middle) and Windows 8.1 (right)