[C#] .NET 6 で、現在開いている Word/Excel/PowerPoint を列挙する

Program.cs

using System;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Runtime.InteropServices.ComTypes;
using Word = Microsoft.Office.Interop.Word;
using Excel = Microsoft.Office.Interop.Excel;
using PowerPoint = Microsoft.Office.Interop.PowerPoint;

if (!OperatingSystem.IsWindows()) { throw new PlatformNotSupportedException(); }

var objects = ROTManager.GetObjects();
foreach (var obj in objects)
{
    // Console.WriteLine($"{obj.ClassID}, {obj.MonikerType}, {obj.DisplayName}");
    if (obj.ComObject is Word.Document document)
    {
        Console.WriteLine($"Saved={document.Saved}, File={document.FullName}");
        if (document.ActiveWindow is { } w)
        {
            Console.WriteLine($"\tHwnd=0x{w.Hwnd:X}, Caption={w.Caption}");
            Marshal.ReleaseComObject(w);
        }
    }
    else if (obj.ComObject is Excel.Workbook book)
    {
        Console.WriteLine($"Saved={book.Saved}, File={book.FullName}");
        var app = book.Application!;
        Console.WriteLine($"\tHwnd=0x{app.Hwnd:X}, Instance={app.HinstancePtr}");
        if (app.ActiveWindow is { } w)
        {
            Console.WriteLine($"\tHwnd=0x{w.Hwnd:X}, Caption={w.Caption}");
            Marshal.ReleaseComObject(w);
        }
        Marshal.ReleaseComObject(app);
    }
    else if (obj.ComObject is PowerPoint.Presentation presentation)
    {
        Console.WriteLine($"Saved={presentation.Saved}, File={presentation.FullName}");
        var app = presentation.Application!;
        if (app.ActiveWindow is { } w)
        {
            Console.WriteLine($"\tHWND=0x{w.HWND:X}, Caption={w.Caption}");
            Marshal.ReleaseComObject(w);
        }
        Marshal.ReleaseComObject(app);
    }
    Marshal.ReleaseComObject(obj.ComObject);
}


public readonly record struct ActiveObject(object ComObject, SystemMoniker MonikerType, Guid ClassID, string DisplayName);
public enum SystemMoniker
{
    None = 0,
    GenericComposite = 1,
    FileMoniker = 2,
    AntiMoniker = 3,
    ItemMoniker = 4,
    PointerMoniker = 5,
    UrlMoniker = 6,
    ClassMoniker = 7,
    ObjRefMoniker = 8,
    SessionMoniker = 9,
    LuaMoniker = 10,
}

public static class ROTManager
{
    const int S_OK = 0;

    [DllImport("ole32.dll", PreserveSig = false)]
    private static extern IBindCtx? CreateBindCtx(uint reserved = 0u);

    internal static ActiveObject[] GetObjects()
    {
        if (!OperatingSystem.IsWindows()) { throw new PlatformNotSupportedException(); }

        var results = new List<ActiveObject>();

        var (rot, enumMoniker) = (default(IRunningObjectTable), default(IEnumMoniker));
        IBindCtx? ctx = CreateBindCtx();
        ctx?.GetRunningObjectTable(out rot);
        rot?.EnumRunning(out enumMoniker);
        if (ctx is { } && rot is { } && enumMoniker is { })
        {
            while (true)
            {
                var monikers = new IMoniker[1];
                if (enumMoniker.Next(1, monikers, IntPtr.Zero) != S_OK) { break; }
                var moniker = monikers[0];
                try
                {
                    var monikerType = (moniker.IsSystemMoniker(out int pdwMksys) == S_OK) ? (SystemMoniker)pdwMksys : SystemMoniker.None;
                    moniker.GetDisplayName(ctx, moniker, out var displayName);
                    moniker.GetClassID(out var classID);
                    rot.GetObject(moniker, out object comObject);
                    results.Add(new ActiveObject(comObject, monikerType, classID, displayName));
                }
                finally
                {
                    Marshal.FinalReleaseComObject(moniker);
                    moniker = null;
                }
            }
        }
        if (enumMoniker is not null) { Marshal.FinalReleaseComObject(enumMoniker); }
        if (rot is not null) { Marshal.FinalReleaseComObject(rot); }
        if (ctx is not null) { Marshal.FinalReleaseComObject(ctx); }
        return results.ToArray();
    }

}

元ネタ：
https://social.msdn.microsoft.com/Forums/ja-JP/009a948a-b84f-4bf1-8024-a0fbda7327f7/c123912969422312125011245712450124641252112454125311248912394ex?forum=windowsgeneraldevelopmentissuesja