Apply a thumbnail

It's not hard to do, thanks to SharpShell, which can be downloaded from NUGET. I had to do this for a project a while ago. I used an article from the Code Project. I'll give you a brief explanation, but on the site you will find a full explanation and the download link for the example.

link

Basically what you should do is create a COM component. This component will be registered in windows, and explorer can use it to render your thumbnails.

Create a new project in C #, and add the references to System.Windows.Forms and System.Drawing . Open the Package Manager Console and type Install-Package SharpShell . With all references linked to the project, create a new class and copy the example below. Remembering that all this code was taken from the codeproject article.

using SharpShell.Attributes;
using SharpShell.SharpThumbnailHandler;
using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Imaging;
using System.Drawing.Text;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;

namespace TxtThumbnailHandler
{
    /// <summary>
    /// The TxtThumbnailHandler is a ThumbnailHandler for text files.
    /// </summary>
    [ComVisible(true)] //Torna ele um componente "visível" para a COM
    [COMServerAssociation(AssociationType.FileExtension, ".txt")] // Associa este coponente ao tipo de associação de Extensão de Arquivos, e informa que o tipo de arquivo é neste caso, o txt.
    public class TxtThumbnailHandler : SharpThumbnailHandler
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="TxtThumbnailHandler"/> class.
        /// </summary>
        public TxtThumbnailHandler()
        {
            //  Create our lazy objects.
            lazyThumbnailFont = new Lazy<Font>(() => new Font("Courier New", 12f));
            lazyThumbnailTextBrush = new Lazy<Brush>(() => new SolidBrush(Color.Black));
        }

        /// <summary>
        /// Gets the thumbnail image.
        /// </summary>
        /// <param name="width">The width of the image that should be returned.</param>
        /// <returns>
        /// The image for the thumbnail.
        /// </returns>
        protected override Bitmap GetThumbnailImage(uint width)
        {
            //  Tenta abrir uma stream com o StreamReader.
            try
            {
                using (var reader = new StreamReader(SelectedItemStream))
                {
                    //  Read up to ten lines of text.
                    var previewLines = new List<string>();
                    for (int i = 0; i < 10; i++)
                    {
                        var line = reader.ReadLine();
                        if (line == null)
                            break;
                        previewLines.Add(line);
                    }

                    //  Chama a função que Realiza a geração do thumbnail.
                    return CreateThumbnailForText(previewLines, width);
                }
            }
            catch (Exception exception)
            {
               // Faz algo, tipo gravar num log
                return null;
            }
        }

        /// <summary>
        /// Creates the thumbnail for text, using the provided preview lines.
        /// </summary>
        /// <param name="previewLines">The preview lines.</param>
        /// <param name="width">The width.</param>
        /// <returns>
        /// A thumbnail for the text.
        /// </returns>
        private Bitmap CreateThumbnailForText(IEnumerable<string> previewLines, uint width)
        {
            //  Tamanho do Bitmap
            var thumbnailSize = new Size((int)width, (int)width);

            //  Cria o bitmap.
            var bitmap = new Bitmap(thumbnailSize.Width, thumbnailSize.Height, PixelFormat.Format32bppArgb);

            //  Cria um objeto graphics para manipular o bitmap
            using (var graphics = Graphics.FromImage(bitmap))
            {
                //  Habilita o antialiasing
                graphics.TextRenderingHint = TextRenderingHint.AntiAlias;

                // Desenha o fundo do thumbnail
                // Repare que aqui a imagem do fundo do thumbnail está armazenada em um arquivo de recursos
                graphics.DrawImage(Properties.Resources.Page, 0, 0, thumbnailSize.Width, thumbnailSize.Height);

                //  Create offsets for the text.
                var xOffset = width * 0.2f;
                var yOffset = width * 0.3f;
                var yLimit = width - yOffset;

                graphics.Clip = new Region(new RectangleF(xOffset, yOffset, thumbnailSize.Width - (xOffset * 2), thumbnailSize.Height - width * .1f));

                //  Renderiza cada linha do texto
                foreach (var line in previewLines)
                {
                    graphics.DrawString(line, lazyThumbnailFont.Value, lazyThumbnailTextBrush.Value, xOffset, yOffset);
                    yOffset += 14f;
                    if (yOffset + 14f > yLimit)
                        break;
                }
            }

            //  Retorna o bitmap
            return bitmap;
        }

        /// <summary>
        /// The lazy thumbnail font.
        /// </summary>
        private readonly Lazy<Font> lazyThumbnailFont;

        /// <summary>
        /// The lazy thumbnail text brush.
        /// </summary>
        private readonly Lazy<Brush> lazyThumbnailTextBrush;
    }
}

As you can read in the comment above, it is necessary to load the thumbnail background image into a resource file, and use it in the line marked.

Once this is done, you must give a "Strong Name" for your project. - In the solution explorer, right click on the project  and click properties - Click on the Signing tab - Check the option Sign the Assembly (Sign the Assembly) - In the dropdown below select new. - A dialog box will open. - Enter a name for your assembly. - Uncheck the password option and click OK.

Once you've done this, just compile your code and test.

To test your shel extension, use Server Manager, which ships with sharpshell tools. You can also download the program from the sharpshell repository:

link

Any questions just ask.