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Customizing Image Loading in Markdown

The Markdown control supports custom image loading via the ImageLoader property. This allows you to handle image formats such as SVG, remote images, or any custom logic for image resolution.

Example: Loading SVG Images​

Required Packages​

To use the custom image loader example above, you need to install the following NuGet packages:

 dotnet add package Avalonia.Svg.Skia

Implementation​

Below is an example of a custom image loader that supports SVG images:

using Avalonia.Controls;
using Avalonia.Media.Imaging;
using Avalonia.Svg.Skia;
using System;
using System.IO;
using System.Net.Http;
using System.Text;
using System.Threading.Tasks;

public class CustomImageLoader : MarkdownImageLoader
{
    public override async Task<IImage?> LoadImageAsync(string url)
    {
        IImage? image = null;

        if (Uri.TryCreate(url, UriKind.Absolute, out var uri))
        {
            Stream? stream = null;

            if (uri.Scheme == "http" || uri.Scheme == "https")
            {
                stream = await DownloadImage(uri);
            }
            else if (uri.Scheme == "file" && File.Exists(uri.LocalPath))
            {
                stream = File.OpenRead(uri.LocalPath);
            }

            if (stream is null)
            {
                return null;
            }

            using (stream)
            {
                if (IsSvgFile(stream))
                {
                    var svg = new SvgImage
                    {
                        Source = SvgSource.LoadFromStream(stream)
                    };

                    image = svg;
                }
                else
                {
                    image = new Bitmap(stream);
                }
            }
        }

        return image;
    }

    private static async Task<Stream> DownloadImage(Uri url)
    {
        using var client = new HttpClient();
        using var response = await client.GetAsync(url).ConfigureAwait(false);
        using var stream = await response.Content.ReadAsStreamAsync().ConfigureAwait(false);
        var memoryStream = new MemoryStream();
        await stream.CopyToAsync(memoryStream).ConfigureAwait(false);
        memoryStream.Position = 0;
        return memoryStream;
    }

    private static bool IsSvgFile(Stream stream)
    {
        if (stream == null || stream.Length == 0)
            return false;
        try
        {
            const int bufferSize = 512;
            byte[] buffer = new byte[Math.Min(bufferSize, stream.Length)];
            int bytesRead = stream.Read(buffer, 0, buffer.Length);
            string header = Encoding.UTF8.GetString(buffer, 0, bytesRead);
            return header.Contains("<svg", StringComparison.OrdinalIgnoreCase);
        }
        catch
        {
            return false;
        }
        finally
        {
            stream.Position = 0;
        }
    }
}

Usage​

Assign your custom loader to the ImageLoader property:

var markdown = new Markdown
{
    Text = "![SVG Image](https://example.com/image.svg)",
    ImageLoader = new CustomImageLoader()
};

When to Use​

  • To support SVG images in Markdown
  • To implement custom caching or authentication for images

See Also​