SOLIDWORKS 3D offers users a dark and a light theme.

There is a setting in Windows 10 that automatically turn on or off theme selection in third-party applications. SOLIDWORKS does not use that feature so it’s about time we wrote an article to show how a custom add-in can automatically pick up that Windows setting. First, to turn on or off app theme mode, you need to :

• Type theme in the Windows search bar and pick the first result.
• Click on Colors on the sidebar and you will get this window.

Clicking light or dark under “Choose your default app mode” will switch the theme in your applications. A good example is Google Chrome.

The source code of the add-in is available on our GitHub. It’s made of two classes:
– swAddIn.cs: This is the add-in class.
– WindowsThemeManager.cs : This class listens for registry changes when the default app mode values.

swAddIn.cs

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	using Microsoft.Win32;
	using SolidWorks.Interop.sldworks;
	using SolidWorks.Interop.swconst;
	using SolidWorks.Interop.swpublished;
	using System;
	using System.Runtime.InteropServices;
	using System.Windows.Forms;
	namespace WindowsThemeSync
	{
	[Guid("36EB446E-E8D2-4F2A-AE07-B45D8DD92694"), ComVisible(true)]
	public class WindowsThemeSyncAddIn : ISwAddin
	{
	#region fields
	public SldWorks SOLIDWORKS { get; private set; }
	public int SessionCookie { get; private set; }
	public static object AddInName { get; private set; } = "Windows 10 App Mode Sync - Blue Byte Systems Inc.";
	public static object AddInDescription { get; private set; } = "Syncs your SOLIDWORKS theme with Windows 10 default app mode.";
	#endregion
	/// <summary>
	/// This method is called when the add-in is activated in SOLIDWORKS.
	/// </summary>
	/// <param name="ThisSW">The this sw.</param>
	/// <param name="Cookie">The cookie.</param>
	/// <returns></returns>
	public bool ConnectToSW(object ThisSW, int Cookie)
	{
	try
	{
	SOLIDWORKS = ThisSW as SldWorks;
	SessionCookie = Cookie;
	SOLIDWORKS.SetAddinCallbackInfo(0, this, SessionCookie);
	// sync the existing theme from the Windows settings
	RefreshTheme();
	// start watching for theme registry changes
	WindowsThemeManager.WindowsThemeChanged += WindowsThemeManager_WindowsThemeChanged;
	WindowsThemeManager.StartWatchingForThemeChanges();
	return true;
	}
	catch (Exception e)
	{
	// in case something goes wrong
	// this might fail an older Windows OS
	MessageBox.Show($"Message = {e.Message} Stacktrace: {e.StackTrace}");
	return false;
	}
	}
	/// <summary>
	/// Fired when the Windows default app mode value in the registry changes
	/// </summary>
	/// <param name="sender">The sender.</param>
	/// <param name="e">The e.</param>
	private void WindowsThemeManager_WindowsThemeChanged(object sender, Theme_e e)
	{
	var currentTheme = (swInterfaceBrightnessTheme_e)SOLIDWORKS.GetUserPreferenceIntegerValue((int)swUserPreferenceIntegerValue_e.swSystemColorsBackground);
	switch (e)
	{
	case Theme_e.Light:
	if (currentTheme != swInterfaceBrightnessTheme_e.swInterfaceBrightnessTheme_Light)
	SOLIDWORKS.SetUserPreferenceIntegerValue((int)swUserPreferenceIntegerValue_e.swSystemColorsBackground, (int)swInterfaceBrightnessTheme_e.swInterfaceBrightnessTheme_Light);
	break;
	case Theme_e.Dark:
	if (currentTheme != swInterfaceBrightnessTheme_e.swInterfaceBrightnessTheme_Dark)
	SOLIDWORKS.SetUserPreferenceIntegerValue((int)swUserPreferenceIntegerValue_e.swSystemColorsBackground, (int)swInterfaceBrightnessTheme_e.swInterfaceBrightnessTheme_Dark);
	break;
	default:
	break;
	}
	}
	/// <summary>
	/// Refreshes the theme.
	/// </summary>
	public void RefreshTheme()
	{
	var theme = WindowsThemeManager.GetWindowsTheme();
	var currentTheme = (swInterfaceBrightnessTheme_e)SOLIDWORKS.GetUserPreferenceIntegerValue((int)swUserPreferenceIntegerValue_e.swSystemColorsBackground);
	switch (theme)
	{
	case Theme_e.Light:
	if (currentTheme != swInterfaceBrightnessTheme_e.swInterfaceBrightnessTheme_Light)
	SOLIDWORKS.SetUserPreferenceIntegerValue((int)swUserPreferenceIntegerValue_e.swSystemColorsBackground, (int)swInterfaceBrightnessTheme_e.swInterfaceBrightnessTheme_Light);
	break;
	case Theme_e.Dark:
	if (currentTheme != swInterfaceBrightnessTheme_e.swInterfaceBrightnessTheme_Dark)
	SOLIDWORKS.SetUserPreferenceIntegerValue((int)swUserPreferenceIntegerValue_e.swSystemColorsBackground, (int)swInterfaceBrightnessTheme_e.swInterfaceBrightnessTheme_Dark);
	break;
	default:
	break;
	}
	}
	/// <summary>
	/// Gets called when you deativate the add-in in SOLIDWORKS
	/// </summary>
	/// <returns></returns>
	public bool DisconnectFromSW()
	{
	try
	{
	// stop watch for registry changes
	WindowsThemeManager.StopWatchingForThemeChanges();
	return true;
	}
	catch (Exception e)
	{
	//todo: log ex
	return false;
	}
	}
	#region com registration
	[ComRegisterFunction]
	private static void RegisterAssembly(Type t)
	{
	try
	{
	string KeyPath = string.Format(@"SOFTWARE\SolidWorks\AddIns\{0:b}", t.GUID);
	RegistryKey rk = Registry.LocalMachine.CreateSubKey(KeyPath);
	rk.SetValue("Title", AddInName); // Title
	rk.SetValue("Description", AddInDescription); // Description
	rk.SetValue(null, 1); // startup parameter (loads addin automatically upon SOLIDWORKS startup)
	}
	catch (Exception e)
	{
	//todo: msgbox ex
	throw e;
	}
	}
	[ComUnregisterFunction]
	private static void UnregisterAssembly(Type t)
	{
	try
	{
	bool Exist = false;
	string KeyPath = string.Format(@"SOFTWARE\SolidWorks\AddIns\{0:b}", t.GUID);
	using (RegistryKey Key = Registry.LocalMachine.OpenSubKey(KeyPath))
	{
	if (Key != null)
	Exist = true;
	else
	Exist = false;
	}
	if (Exist)
	Registry.LocalMachine.DeleteSubKeyTree(KeyPath);
	}
	catch (Exception e)
	{
	//todo: msgbox ex
	throw e;
	}
	}
	#endregion
	}
	}

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WindowsThemeManager.cs:

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	using Microsoft.Win32;
	using System;
	using System.Management;
	using System.Security.Principal;
	namespace WindowsThemeSync
	{
	public enum Theme_e
	{
	Undefined,
	Light,
	Dark
	}
	public class WindowsThemeManager
	{
	#region Public Events
	public static event EventHandler<Theme_e> WindowsThemeChanged;
	#endregion
	#region Private Fields
	private static ManagementEventWatcher watcher;
	#endregion
	#region Private Properties
	#endregion
	#region Public Properties
	public static bool IsWatching { get; private set; } = false;
	#endregion
	#region Private Constructors
	private WindowsThemeManager()
	{
	}
	#endregion
	#region Private Methods
	private const string RegistryKeyPath = @"Software\Microsoft\Windows\CurrentVersion\Themes\Personalize";
	private const string RegistryValueName = "AppsUseLightTheme";
	public static Theme_e GetWindowsTheme()
	{
	try
	{
	var key = Registry.CurrentUser.OpenSubKey(RegistryKeyPath);
	var registryValueObject = key?.GetValue(RegistryValueName);
	if (registryValueObject == null)
	{
	return Theme_e.Light;
	}
	var registryValue = (int)registryValueObject;
	key.Close();
	return registryValue > 0 ? Theme_e.Light : Theme_e.Dark;
	}
	catch (Exception)
	{
	return Theme_e.Undefined;
	}
	}
	private static void Watcher_EventArrived(object sender, EventArrivedEventArgs e)
	{
	try
	{
	var ret = GetWindowsTheme();
	WindowsThemeChanged?.Invoke(null, ret);
	}
	catch (System.Exception)
	{
	// needs to add logger here
	}
	}
	#endregion
	#region Public Methods
	public static void StartWatchingForThemeChanges()
	{
	try
	{
	if (IsWatching == true)
	throw new Exception("Object already watching registry entry");
	var currentUser = WindowsIdentity.GetCurrent();
	WqlEventQuery query = new WqlEventQuery(
	"SELECT * FROM RegistryValueChangeEvent WHERE " +
	"Hive = 'HKEY_USERS' " +
	$@"AND KeyPath='{currentUser.User.Value}\\Software\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize' AND ValueName='{RegistryValueName}'");
	watcher = new ManagementEventWatcher(query);
	watcher.EventArrived -= Watcher_EventArrived;
	watcher.EventArrived += Watcher_EventArrived;
	watcher.Start();
	IsWatching = true;
	}
	catch (Exception)
	{
	}
	}
	public static void StopWatchingForThemeChanges()
	{
	if (watcher != null)
	{
	watcher.Stop();
	watcher.Dispose();
	watcher = null;
	}
	IsWatching = false;
	}
	#endregion
	}
	}

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