How to check if the silverlight application is in design mode?

As a siverlight control developer, it's very important to know when the silverlight control is in design mode, and then we can design the beautiful design skin for our control. Here is a part of tips:

/// <summary>
/// Provides a custom implementation of DesignerProperties.GetIsInDesignMode
/// to work around an issue.
/// </summary>
internal static class DesignerProperties
{
    /// <summary>
    /// Returns whether the control is in design mode (running under Blend
    /// or Visual Studio).
    /// </summary>
    /// <param name="element">The element from which the property value is
    /// read.</param>
    /// <returns>True if in design mode.</returns>
    [SuppressMessage("Microsoft.Usage", "CA1801:ReviewUnusedParameters", MessageId = "element", Justification =
        "Matching declaration of System.ComponentModel.DesignerProperties.GetIsInDesignMode (which has a bug and is not reliable).")]
    public static bool GetIsInDesignMode(DependencyObject element)
    {
        if (!_isInDesignMode.HasValue)
        {
            _isInDesignMode =
                (null == Application.Current) ||
                Application.Current.GetType() == typeof(Application);
        }
        return _isInDesignMode.Value;
    }

    /// <summary>
    /// Stores the computed InDesignMode value.
    /// </summary>
    private static bool? _isInDesignMode;
}

The code comes from http://blogs.msdn.com/delay/archive/2009/02/26/designerproperties-getisindesignmode-forrealz-how-to-reliably-detect-silverlight-design-mode-in-blend-and-visual-studio.aspx