Change theme at runtime

Question

I have a WPF application with a theme (ShinyRed.xaml) and I want to have a button that when clicked changes the theme to ShinyBlue.xaml

I load in the theme initially

Answer 1

H.B.'s answer did not run for me, I had to do this (works, tested):

Uri dictUri = new Uri(@"/Resources/Themes/MyTheme.xaml", UriKind.Relative);
ResourceDictionary resourceDict = Application.LoadComponent(dictUri) as ResourceDictionary;
Application.Current.Resources.MergedDictionaries.Clear();
Application.Current.Resources.MergedDictionaries.Add(resourceDict);

To pretty it up:

// Place in App.xaml.cs
public void ChangeTheme(Uri uri)
{
    ResourceDictionary resourceDict = Application.LoadComponent(uri) as ResourceDictionary;
    Application.Current.Resources.MergedDictionaries.Clear();
    Application.Current.Resources.MergedDictionaries.Add(resourceDict);
}

// Example Usage (anywhere in app)
private void ThemeRed_Click(object sender, RoutedEventArgs e)
{
    var app = App.Current as App;
    app.ChangeTheme(new Uri(@"/Resources/Themes/RedTheme.xaml", UriKind.Relative));      
}