Themes

WPF UI supports themes. You set the default theme in App.xaml, with the help of an automatic resources importer.

<Application
  ...
  xmlns:ui="http://schemas.lepo.co/wpfui/2022/xaml">
  <Application.Resources>
    <ResourceDictionary>
      <ResourceDictionary.MergedDictionaries>
        <ui:ThemesDictionary Theme="Dark" />
        <ui:ControlsDictionary />
      </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>
  </Application.Resources>
</Application>

Or, you can add WPF UI resources manually.

<Application>
  <Application.Resources>
    <ResourceDictionary>
      <ResourceDictionary.MergedDictionaries>
        <ResourceDictionary Source="pack://application:,,,/Wpf.Ui;component/Resources/Theme/Dark.xaml" />
        <ResourceDictionary Source="pack://application:,,,/Wpf.Ui;component/Resources/Wpf.Ui.xaml" />
      </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>
  </Application.Resources>
</Application>

Change on the fly

If you want to change the theme while the application is running, you can call the static Apply method of the Theme class.

Wpf.Ui.Appearance.ApplicationThemeManager.Apply(
  Wpf.Ui.Appearance.ApplicationTheme.Light, // Theme type
  Wpf.Ui.Controls.WindowBackdropType.Mica,  // Background type
  true                                      // Whether to change accents automatically
);

Automatic change

The theme can be changed automatically when the operating system changes its background or accent using the SystemThemeWatcher class.

namespace MyApp;

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();

        Loaded += (sender, args) =>
        {
            Wpf.Ui.Appearance.SystemThemeWatcher.Watch(
                this,                                    // Window class
                Wpf.Ui.Controls.WindowBackdropType.Mica, // Background type
                true                                     // Whether to change accents automatically
            );
        };
    }
}