How to detect Windows dark mode

Question

In the Windows settings, dark mode is enabled for Windows and light mode is enabled for applications.

The following keys are missing from the registry:

HKCU\Microsoft\Windows\CurrentVersion\Themes\Personalize.
HKLM\Microsoft\Windows\CurrentVersion\Themes\Personalize

How can I detect Windows dark mode in a WPF application?

Answer 1

It depends on Windows versions
On recent OS (>= Windows 10 1903) :

    [DllImport("UXTheme.dll", SetLastError = true, EntryPoint = "#138")] 
    public static extern bool ShouldSystemUseDarkMode();

test :

    bool bRet = ShouldSystemUseDarkMode();

Answer 2

If you want to have your application respond to light and dark mode you can start by adding the NuGet package Microsoft.Windows.SDK.Contracts

Lets create a simple View Model which returns a title and the brushes to display the data in the right color.

First lets get the Colors to use for the brushes

    UISettings settings = new UISettings();
    var foreground = settings.GetColorValue(UIColorType.Foreground);
    var background = settings.GetColorValue(UIColorType.Background);

Now we can create the brushes to use

    Color myforeColor = Color.FromArgb(foreground.A, foreground.R, foreground.G, foreground.B);
    ForeBrush = new SolidColorBrush(myforeColor);

    Color mybackColor = Color.FromArgb(background.A, background.R, background.G, background.B);
    BackBrush=new SolidColorBrush(mybackColor);

Here is the whole View Model

public class MainViewModel:INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;

 // This method is called by the Set accessor of each property.
 // The CallerMemberName attribute that is applied to the optional propertyName
 // parameter causes the property name of the caller to be substituted as an argument.
 private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
 {
      if (PropertyChanged != null)
      {
          PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
      }
  }


  public MainViewModel()
  {
      UISettings settings = new UISettings();
      var foreground = settings.GetColorValue(UIColorType.Foreground);
      var background = settings.GetColorValue(UIColorType.Background);
      Color myforeColor = Color.FromArgb(foreground.A, foreground.R, foreground.G, foreground.B);
      ForeBrush = new SolidColorBrush(myforeColor);

      Color mybackColor = Color.FromArgb(background.A, background.R, background.G, background.B);
      BackBrush=new SolidColorBrush(mybackColor);
      Title = "Welcome to WPF";
  }

  private SolidColorBrush foreBrush = new SolidColorBrush(Colors.Black);
  public SolidColorBrush ForeBrush
  {
      get
      {
           return foreBrush;
      }
      set
      {
          foreBrush = value;
          NotifyPropertyChanged();
      }
  }


   private SolidColorBrush backBrush = new SolidColorBrush(Colors.White);
   public SolidColorBrush BackBrush
   {
      get
      {
            return backBrush;
       }
       set
       {
           backBrush = value;
           NotifyPropertyChanged();
       }
    }

   private string title;

   public string Title
   {
       get { return title; }
       set
       {
            title = value;
            NotifyPropertyChanged();
        }
    }

}

An alternate method to do this is to look in the registry

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Themes\Personalize\AppsUseLightTheme. In the value of the key is 1 Windows 10 is in Light mode.

Depending on the value in the registry you would have to set the brush colors.

Here is a link to an example
https://github.com/vb2ae/WPFLightDarkMode