从 URL 加载图像作为 base64 字符串

Answer 1

在我看来，您需要将仅在您的 HTML 中需要的 base64 部分与从响应中获取数据分开。只需从 URL 中获取数据作为二进制数据并将其转换为 base64。使用

HttpClient

使这变得简单：

public async static Task<string> GetImageAsBase64Url(string url)
{
    var credentials = new NetworkCredential(user, pw);
    using (var handler = new HttpClientHandler { Credentials = credentials })
    using (var client = new HttpClient(handler))
    {
        var bytes = await client.GetByteArrayAsync(url);
        return "image/jpeg;base64," + Convert.ToBase64String(bytes);
    }
}

这假设图像总是 will 是 JPEG。如果它有时可能是不同的内容类型，您可能希望以

HttpResponse

的形式获取响应并使用它来传播内容类型。

我怀疑你可能也想在这里添加缓存 :)

Answer 2

 using (HttpClient client = new HttpClient())
                {
                    try
                    {
                        using (Stream stream = await client.GetStreamAsync(uri))
                        {
                            if (stream == null)
                                return (Picture)null;
                            byte[] buffer = new byte[16384];
                            using (MemoryStream ms = new MemoryStream())
                            {
                                while (true)
                                {
                                    int num = await stream.ReadAsync(buffer, 0, buffer.Length, cancellation);
                                    int read;
                                    if ((read = num) > 0)
                                        ms.Write(buffer, 0, read);
                                    else
                                        break;
                                }
                                imageData = Convert.ToBase64String(ms.ToArray());
                            }
                            buffer = (byte[])null;
                        } 
                    }
                    catch (Exception ex)
                    {
                         
                    }
                }

Answer 3

此解决方案适用于.NET Core 3.1

  public static async Task<string> ImageUrlToBase64(string imageUrl)
  {
     using var httClient = new HttpClient();
     var imageBytes = await httClient.GetByteArrayAsync(imageUrl);                
     return Convert.ToBase64String(imageBytes);
  }

var encodedBase64 = WebUtility.UrlEncode(await ImageUrlToBase64(ImageUrl));

如果前端有JS，使用如下代码：

var base64String = 'data:image/png;base64,' + encodedBase64;
$("#photo").attr('src', base64String); 

Answer 4

您必须先从磁盘获取图像，然后将其转换为 byte[]，然后再转换为 base64。

    public string ImageToBase64(Image image, System.Drawing.Imaging.ImageFormat format)
    {
      using (MemoryStream ms = new MemoryStream())
      {
    // Convert Image to byte[]
    image.Save(ms, format);
    byte[] imageBytes = ms.ToArray();

    // Convert byte[] to Base64 String
    string base64String = Convert.ToBase64String(imageBytes);
    return base64String;
  }
}