/// <summary>
/// Contains information provided when registering for notifications.
/// </summary>
/// <remarks>
/// Corresponds to the native <c>WLAN_NOTIFICATION_DATA</c> type.
/// </remarks>
[StructLayout(LayoutKind.Sequential)]
public struct WLAN_NOTIFICATION_DATA
{
    /// <summary>
    /// Specifies where the notification comes from.
    /// </summary>
    /// <remarks>
    /// On Windows XP SP2, this field must be set to <see cref="WlanNotificationSource.None"/>, <see cref="WlanNotificationSource.All"/> or <see cref="WlanNotificationSource.ACM"/>.
    /// </remarks>
    public WLAN_NOTIFICATION_SOURCE notificationSource;
    /// <summary>
    /// Indicates the type of notification. The value of this field indicates what type of associated data will be present in <see cref="dataPtr"/>.
    /// </summary>
    public int notificationCode;
    /// <summary>
    /// Indicates which interface the notification is for.
    /// </summary>
    public Guid interfaceGuid;
    /// <summary>
    /// Specifies the size of <see cref="dataPtr"/>, in bytes.
    /// </summary>
    public int dataSize;
    /// <summary>
    /// Pointer to additional data needed for the notification, as indicated by <see cref="notificationCode"/>.
    /// </summary>
    public IntPtr dataPtr;

    /// <summary>
    /// Gets the notification code (in the correct enumeration type) according to the notification source.
    /// </summary>
    public object NotificationCode
    {
    get
    {
        if (notificationSource == WLAN_NOTIFICATION_SOURCE.MSM)
        return (WLAN_NOTIFICATION_CODE_MSM)notificationCode;
        else if (notificationSource == WLAN_NOTIFICATION_SOURCE.ACM)
        return (WLAN_NOTIFICATION_CODE_ACM)notificationCode;
        else
        return notificationCode;
    }

    }
}

VB Definition:

<StructLayout(LayoutKind.Sequential)> _
    Public Structure WLAN_NOTIFICATION_DATA
        Public notificationSource As WLAN_NOTIFICATION_SOURCE
        Public m_notificationCode As Integer
        Public interfaceGuid As Guid
        Public dataSize As Integer
        Public dataPtr As IntPtr

        Public ReadOnly Property NotificationCode() As Object
        Get
            If notificationSource = WLAN_NOTIFICATION_SOURCE.ACM Then
            Return DirectCast(m_notificationCode, WLAN_NOTIFICATION_CODE_ACM)
            Else
            Return m_notificationCode
            End If
        End Get
        End Property

    End Structure