C#+js 打印在线pdf

提供一个pdf在线浏览链接（如电子发票），点击不同按钮后唤起对应打印页面

思路1：前端使用iframe展示，点击调用windows.print()。

结果：不可行。存在跨域问题，且前端显示的pdf很小，调用print也无法显示；

 

思路2：前端传递给后端url，url请求下载到服务器后，文件转bitmap回传base64

结果：可行。有点麻烦，但是没有更好的解决办法了。

 

后端代码：

注意1：pdf文件下载到本地后，Nuget下载FreeSpire.Pdf，此插件免费，但是打印页数有限制，好像是10张。

参考文档 https://www.e-iceblue.cn/conversion/convert-pdf-to-doc-image-and-xps.html

注意2：如果下载的图片不清晰，要在SaveAsImage调整一下dpiX 和dpiY

public async Task<string> GetPDFFile(string urlNet,string einvoice) 
{
  var base64 = string.Empty;
  var baseUri = ConfigurationManager.AppSettings["pdfUri"];//基址
  var path = ConfigurationManager.AppSettings["pdfSavePath"];//保存到本地的图片地址
  var completePdfFileName = $"{path}{einvoice}.pdf";//保存到本地的pdf的路径和文件名
  
  var isExist = File.Exists(completePdfFileName);
  if (!isExist) 
  {
      var httpClient = new HttpClient{BaseAddress = new Uri(baseUri)};
      var request = new HttpRequestMessage{Method = new HttpMethod("GET")};//请求下载
      request.Headers.Add("context-type", "application/pdf");
      request.RequestUri = new Uri($"{urlNet}");
      var response = await httpClient.SendAsync(request);
      var stream = response.Content.ReadAsStreamAsync().Result;
      using (var fs = new FileStream(completePdfFileName, FileMode.Create)) 
      {
          var buffer = new byte[stream.Length];
          await stream.ReadAsync(buffer, 0, buffer.Length);
          fs.Write(buffer, 0, buffer.Length);
      }

      var isExist2 = File.Exists(completePdfFileName);
      if (isExist2) 
      {
          logger.Info($"文件下载成功：{completePdfFileName}");
          //初始化PdfDocument实例
          PdfDocument doc = new PdfDocument();
          //加载PDF文档
          doc.LoadFromFile(completePdfFileName);

          //将PDF页转换成bitmap图形
          Image bmp = doc.SaveAsImage(0, 0, 900, 900);//调整分辨率
          //将bitmap图形保存为png图片
          string fileName = string.Format($"{einvoice}.jpg",  1);
          bmp.Save(path + fileName, ImageFormat.Jpeg);
          MemoryStream ms = new MemoryStream();
          bmp.Save(ms, ImageFormat.Jpeg);//转base64
          byte[] arr = new byte[ms.Length];
          ms.Position = 0;
          ms.Read(arr, 0, (int)ms.Length);
          ms.Close();
          base64 = Convert.ToBase64String(arr);

        } else 
        {
          logger.Info($"文件下载失败：{completePdfFileName}");
        }
      } else 
      {
        //初始化PdfDocument实例
        PdfDocument doc = new PdfDocument();
        //加载PDF文档
        doc.LoadFromFile(completePdfFileName);
        Image bmp = doc.SaveAsImage(0, 0, 900, 900);
        //将bitmap图形保存为png图片
        string fileName = string.Format($"{einvoice}.jpg", 1);
        bmp.Save(path + fileName, ImageFormat.Jpeg);
        MemoryStream ms = new MemoryStream();
        bmp.Save(ms, ImageFormat.Jpeg);
        byte[] arr = new byte[ms.Length];
        ms.Position = 0;
        ms.Read(arr, 0, (int)ms.Length);
        ms.Close();
        base64 = Convert.ToBase64String(arr);
      }
  
      return base64;
}

 

前端调用：

获取base64，打开新窗口，显示到img中，同时调用print 

var response = JSON.parse(result);
if (response.Success) {

    var imgdata = "data:image/jpeg;base64," + response.details[0].InvoiceBase64;

    if (imgdata) {
        var win = window.open(imgdata, "_blank");
        win.document.write(` < image id = "img"style = "width:100%;height90%;"src = $ {imgdata} > `);
        var img = win.document.querySelector("#img") as HTMLElement;
        img.onload = () = >{//图片加载完成后调用print
            win.focus();
            win.print();
            win.close();//点击打印或者取消后会自动关闭新页面
        };
    }
}

 

最后效果