画像ファイルのタイトルを書き換えるC#サンプルコード「WindowsSearchの有効活用」

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>

</Project>

using System;
using System.Runtime.InteropServices;

class ImgTitle
{
    // ===== PROPERTYKEY / PROPVARIANT =====

    [StructLayout(LayoutKind.Sequential)]
    struct PROPERTYKEY
    {
        public Guid fmtid;
        public uint pid;
    }

    [StructLayout(LayoutKind.Explicit)]
    struct PROPVARIANT
    {
        [FieldOffset(0)] public ushort vt;
        [FieldOffset(8)] public IntPtr pwszVal;
    }

    enum VARTYPE : ushort
    {
        VT_EMPTY = 0,
        VT_LPWSTR = 31
    }

    // ===== IPropertyStore =====

    [ComImport]
    [Guid("886D8EEB-8CF2-4446-8D02-CDBA1DBDCF99")]
    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    interface IPropertyStore
    {
        uint GetCount(out uint cProps);
        uint GetAt(uint iProp, out PROPERTYKEY pkey);
        uint GetValue(ref PROPERTYKEY key, out PROPVARIANT pv);
        uint SetValue(ref PROPERTYKEY key, ref PROPVARIANT pv);
        uint Commit();
    }

    enum GETPROPERTYSTOREFLAGS
    {
        GPS_READWRITE = 0x00000002
    }

    [DllImport("shell32.dll", CharSet = CharSet.Unicode)]
    static extern int SHGetPropertyStoreFromParsingName(
        string pszPath,
        IntPtr pbc,
        GETPROPERTYSTOREFLAGS flags,
        ref Guid riid,
        out IPropertyStore store);

    // ===== System.Title =====

    static readonly PROPERTYKEY PKEY_System_Title = new()
    {
        fmtid = new Guid("F29F85E0-4FF9-1068-AB91-08002B27B3D9"),
        pid = 2
    };

    // ===== エントリポイント =====

    static int Main(string[] args)
    {
        if (args.Length < 1)
        {
            Console.WriteLine("Usage:");
            Console.WriteLine("  ImgTitle <file>");
            Console.WriteLine("  ImgTitle <file> \"New Title\"");
            return 1;
        }

        string path = args[0];
        try
        {
            if (args.Length == 1)
            {
                string? title = GetTitle(path);
                if (title == null) return 1;
                Console.WriteLine(title);
            }
            else
            {
                SetTitle(path, args[1]);
            }
        }
        catch (Exception ex)
        {
            Console.Error.WriteLine(ex.Message);
            return 2;
        }

        return 0;
    }

    // ===== 取得 =====

    static string? GetTitle(string path)
    {
        Guid iid = typeof(IPropertyStore).GUID;

        int hr = SHGetPropertyStoreFromParsingName(
            path,
            IntPtr.Zero,
            GETPROPERTYSTOREFLAGS.GPS_READWRITE,
            ref iid,
            out var store);

        if (hr != 0)
            Marshal.ThrowExceptionForHR(hr);

        PROPERTYKEY key = PKEY_System_Title; // ← readonly対策
        store.GetValue(ref key, out var pv);

        if (pv.vt == (ushort)VARTYPE.VT_EMPTY || pv.pwszVal == IntPtr.Zero)
            return null;

        string result = Marshal.PtrToStringUni(pv.pwszVal)!;
        Marshal.FreeCoTaskMem(pv.pwszVal);

        return result;
    }

    // ===== 変更 =====

    static void SetTitle(string path, string title)
    {
        Guid iid = typeof(IPropertyStore).GUID;

        int hr = SHGetPropertyStoreFromParsingName(
            path,
            IntPtr.Zero,
            GETPROPERTYSTOREFLAGS.GPS_READWRITE,
            ref iid,
            out var store);

        if (hr != 0)
            Marshal.ThrowExceptionForHR(hr);

        var pv = new PROPVARIANT
        {
            vt = (ushort)VARTYPE.VT_LPWSTR,
            pwszVal = Marshal.StringToCoTaskMemUni(title)
        };

        PROPERTYKEY key = PKEY_System_Title;
        store.SetValue(ref key, ref pv);
        store.Commit();

        Marshal.FreeCoTaskMem(pv.pwszVal);
    }
}
/*
ビルド方法
dotnet build -c Release -o ./out
*/