Call secret Explorer API to change tray state

TrayStateChanger.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Interop;

namespace SlackNotifier
{
    public class TrayStateChanger
    {
        public List<NOTIFYITEM> GetTrayItems()
        {
            var instance = new TrayNotify();
            try {
                if (useLegacyInterface()) {
                    return getTrayItemsWin7(instance);
                } else {
                    return getTrayItems(instance);
                }
            } finally {
                Marshal.ReleaseComObject(instance);
            }
        }

        static List<NOTIFYITEM> getTrayItems(TrayNotify instance)
        {
            var notifier = (ITrayNotify)instance;
            var callback = new NotificationCb();
            var handle = default(ulong);

            notifier.RegisterCallback(callback, out handle);
            notifier.UnregisterCallback(handle);
            return callback.items;
        }

        static List<NOTIFYITEM> getTrayItemsWin7(TrayNotify instance)
        {
            var notifier = (ITrayNotifyWin7)instance;
            var callback = new NotificationCb();

            notifier.RegisterCallback(callback);
            notifier.RegisterCallback(null);
            return callback.items;
        }

        class NotificationCb : INotificationCb
        {
            public readonly List<NOTIFYITEM> items = new List<NOTIFYITEM>();

            public void Notify([In] uint nEvent, [In] ref NOTIFYITEM notifyItem)
            {
                items.Add(notifyItem);
            }
        }

        bool useLegacyInterface()
        {
            var ver = Environment.OSVersion.Version;
            if (ver.Major < 6) return true;
            if (ver.Major > 6) return false;

            // Windows 6.2 and higher use new interface
            return ver.Minor <= 1;
        }
    }

    // The known values for NOTIFYITEM's dwPreference member.
    public enum NOTIFYITEM_PREFERENCE {
        // In Windows UI: "Only show notifications."
        PREFERENCE_SHOW_WHEN_ACTIVE = 0,
        // In Windows UI: "Hide icon and notifications."
        PREFERENCE_SHOW_NEVER = 1,
        // In Windows UI: "Show icon and notifications."
        PREFERENCE_SHOW_ALWAYS = 2
    };

    // NOTIFYITEM describes an entry in Explorer's registry of status icons.
    // Explorer keeps entries around for a process even after it exits.
    public struct NOTIFYITEM {
        [MarshalAs(UnmanagedType.LPWStr)]
        string exe_name;    // The file name of the creating executable.

        [MarshalAs(UnmanagedType.LPWStr)]
        string tip;         // The last hover-text value associated with this status
                            // item.

        IntPtr icon;       // The icon associated with this status item.
        IntPtr hwnd;       // The HWND associated with the status item.
        NOTIFYITEM_PREFERENCE  preference;  // Determines the behavior of the icon with respect to
                                            // the taskbar
        uint id;           // The ID specified by the application.  (hWnd, uID) is
                           // unique.
        Guid guid;         // The GUID specified by the application, alternative to
                           // uID.
    };

    [ComImport]
    [Guid("D782CCBA-AFB0-43F1-94DB-FDA3779EACCB")]
    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    interface INotificationCb
    {
        void Notify([In]uint nEvent, [In] ref NOTIFYITEM notifyItem);
    }

    [ComImport]
    [Guid("FB852B2C-6BAD-4605-9551-F15F87830935")]
    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    interface ITrayNotifyWin7
    {
        void RegisterCallback([MarshalAs(UnmanagedType.Interface)]INotificationCb callback);
        void SetPreference([In] ref NOTIFYITEM notifyItem);
        void EnableAutoTray([In] bool enabled);
    }

    [ComImport]
    [Guid("D133CE13-3537-48BA-93A7-AFCD5D2053B4")]
    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    interface ITrayNotify
    {
        void RegisterCallback([MarshalAs(UnmanagedType.Interface)]INotificationCb callback, [Out] out ulong handle);
        void UnregisterCallback([In] ref ulong handle);
        void SetPreference([In] ref NOTIFYITEM notifyItem);
        void EnableAutoTray([In] bool enabled);
        void DoAction([In] bool enabled);
    }

    [ComImport, Guid("25DEAD04-1EAC-4911-9E3A-AD0A4AB560FD")]
    class TrayNotify { }
}