Can WPF themes be used to include multiple skins for an application that can be changed at runtime?

Here is a snippet of code that I used in my application that supported theming. In this example, I have two themes (Default and Classic XP). The theme resources are stored in the DefaultTheme.xaml and ClassicTheme.xaml respectively.

This is the default code in my App.xaml

<Application ...>    <Application.Resources>        <ResourceDictionary>            <ResourceDictionary.MergedDictionaries>                <ResourceDictionary Source="ArtworkResources.xaml" />                <ResourceDictionary Source="DefaultTheme.xaml" />            </ResourceDictionary.MergedDictionaries>            <Style x:Key="SwooshButton" TargetType="ButtonBase">                <!-- style setters -->            </Style>            <!-- more global styles -->        </ResourceDictionary>    </Application.Resources></Application>

Then in the code behind of the App.xaml I have the following method to allow for changing the theme. Basically, what you do is clear the Resource Dictionaries and then reload the dictionary with the new theme.

    private Themes _currentTheme = Themes.Default;    public Themes CurrentTheme    {        get { return _currentTheme; }        set { _currentTheme = value; }    }    public void ChangeTheme(Themes theme)    {        if (theme != _currentTheme)        {            _currentTheme = theme;            switch (theme)            {                default:                case Themes.Default:                    this.Resources.MergedDictionaries.Clear();                    AddResourceDictionary("ArtworkResources.xaml");                    AddResourceDictionary("DefaultTheme.xaml");                    break;                case Themes.Classic:                    this.Resources.MergedDictionaries.Clear();                    AddResourceDictionary("ArtworkResources.xaml");                    AddResourceDictionary("ClassicTheme.xaml");                    break;            }        }    }    void AddResourceDictionary(string source)    {        ResourceDictionary resourceDictionary = Application.LoadComponent(new Uri(source, UriKind.Relative)) as ResourceDictionary;        this.Resources.MergedDictionaries.Add(resourceDictionary);    }

What you'll also need to keep in mind with this approach is that any styles that utilize a theme will need to have a dynamic resource. For example:

<Window Background="{DynamicResource AppBackgroundColor}" />

I don't know of a way of doing this in the framework, but you can do it if you style every control that can change yourself.

The theory is to make the style a DynamicResource and then load the ResourcesDictionary based on the users configuration for the different style.

Here is an article that has an example.