MaterialDesignInXAML/MaterialDesignInXamlToolkit · error · InvalidOperationException

Cannot get ThemeManager outside of a WPF application. Use {n

Error message

Cannot get ThemeManager outside of a WPF application. Use {nameof(ResourceDictionaryExtensions)}.{nameof(ResourceDictionaryExtensions.GetThemeManager)} on the appropriate resource dictionary instead.

What it means

GetThemeManager returns the IThemeManager stored in the application resources and applies the same Application.Current != null guard as the other PaletteHelper methods. When no WPF application is running it throws InvalidOperationException and points to ResourceDictionaryExtensions.GetThemeManager.

Source

Thrown at src/MaterialDesignThemes.Wpf/PaletteHelper.cs:25

        if (Application.Current is null)
            throw new InvalidOperationException($"Cannot get theme outside of a WPF application. Use {nameof(ResourceDictionaryExtensions)}.{nameof(ResourceDictionaryExtensions.GetTheme)} on the appropriate resource dictionary instead.");
        return GetResourceDictionary().GetTheme();
    }

    public virtual void SetTheme(Theme theme)
    {
        if (theme is null) throw new ArgumentNullException(nameof(theme));
        if (Application.Current is null)
            throw new InvalidOperationException($"Cannot set theme outside of a WPF application. Use {nameof(ResourceDictionaryExtensions)}.{nameof(ResourceDictionaryExtensions.SetTheme)} on the appropriate resource dictionary instead.");

        GetResourceDictionary().SetTheme(theme);
        RecreateThemeDictionaries();
    }

    public virtual IThemeManager? GetThemeManager()
    {
        if (Application.Current is null)
            throw new InvalidOperationException($"Cannot get ThemeManager outside of a WPF application. Use {nameof(ResourceDictionaryExtensions)}.{nameof(ResourceDictionaryExtensions.GetThemeManager)} on the appropriate resource dictionary instead.");
        return GetResourceDictionary().GetThemeManager();
    }

    private static ResourceDictionary GetResourceDictionary()
        => Application.Current.Resources.MergedDictionaries.FirstOrDefault(x => x is IMaterialDesignThemeDictionary) ??
            Application.Current.Resources;

    /// <summary>
    /// Removes and readds resource dictionaries with static resource that will be re-evaluated with new theme brushes.
    /// This is primarily here for the obsolete theme brushes.
    /// </summary>
    private static void RecreateThemeDictionaries()
    {
        ResourceDictionary root = Application.Current.Resources;
        for (int i = 0; i < root.MergedDictionaries.Count; i++)
        {
            ResourceDictionary dictionary = root.MergedDictionaries[i];
            if (dictionary["MaterialDesign.Resources.RecreateOnThemeChange"] is bool recreateOnThemeChange && recreateOnThemeChange)

View on GitHub (pinned to 98edec3a0b)

Solutions

1. Call ResourceDictionaryExtensions.GetThemeManager on the relevant ResourceDictionary.
2. Guard with `if (Application.Current is not null) ...` before calling.
3. Obtain the manager from the dictionary you configured via SetTheme, which stores the ThemeManager.

Example fix

// before
var manager = new PaletteHelper().GetThemeManager();
// after
var manager = myResourceDictionary.GetThemeManager();

if (Application.Current is null)
    return myResourceDictionary.GetThemeManager();
return new PaletteHelper().GetThemeManager();

Application.Current is not null

When it happens

Trigger: Calling PaletteHelper.GetThemeManager() outside a running WPF application (tests, designer, console, pre-startup).

Common situations: Subscribing to theme-change notifications in a unit test or design-time context; a service resolving the manager before the app starts.

Related errors

• Cannot get theme outside of a WPF application. Use {nameof(R
• Cannot set theme outside of a WPF application. Use {nameof(R
• theme
• Could not locate required resource with key(s) '{string.Join
• Non primary hues provided.

AI-assisted analysis of MaterialDesignInXAML/MaterialDesignInXamlToolkit@98edec3a0b (2026-08-13). Data as JSON: /api/errors/46a2a709d14ac704. Report an issue: GitHub.