把页面上的图表导出为pdf文件，分享一种请求下载文件的方法

最近客户提出一个需求，就是把页面上的图表导出为pdf文件。

找了很多资料。终于有了点头绪。最主要是参考了HighCharts的做法。http://www.hcharts.cn/

实现原理：把页面图表的svg内容发送到后台，后台生成pdf图片文件流，返回。

但是遇到问题，用jquery的post请求，不能下载文件；用get请求方式，svg数据可能很多，传不过来；最后用了如下方法，创建一个隐藏的form来sumbit.

前台代码片段：

$("#btn").click(function () {
        var f = document.createElement("form");
        document.body.appendChild(f);
        var i = document.createElement("input");
        i.type = "hidden";
        f.appendChild(i);
        i.value = $("#r").html();
        i.name = "svg";

        var j = document.createElement("input");
        j.type = "hidden";
        f.appendChild(j);
        j.value = "pdf";
        j.name = "tpye";
        f.method = "post";
        f.enctype="multipart/form-data"
        f.action = "/Chart/Export";
        f.submit();
    });

后台代码片段：后台会用到两个第三方的dll(itextsharp.dll和Svg.dll)

//HighCharts 导出图片 svg
        //filename type width scale svg
        [HttpPost]
        [ValidateInput(false)]
        public ActionResult Export(FormCollection fc)
        {
            try
            {
                string tType = fc["type"];
                tType = "application/pdf";
                string tSvg = fc["svg"];
                string tFileName = fc["filename"];
                if (string.IsNullOrEmpty(tFileName))
                    tFileName = "chart";
                MemoryStream tData = new MemoryStream(Encoding.UTF8.GetBytes(tSvg));
                MemoryStream tStream = new MemoryStream();
                string tTmp = new Random().Next().ToString();
                string tExt = "";
                string tTypeString = "";

                switch (tType)
                {
                    case "image/png":
                        tTypeString = "-m image/png";
                        tExt = "png";
                        break;
                    case "image/jpeg":
                        tTypeString = "-m image/jpeg";
                        tExt = "jpg";
                        break;
                    case "application/pdf":
                        tTypeString = "-m application/pdf";
                        tExt = "pdf";
                        break;
                    case "image/svg+xml":
                        tTypeString = "-m image/svg+xml";
                        tExt = "svg";
                        break;
                }

                if (tTypeString != "")
                {
                    string tWidth = fc["width"];
                    Svg.SvgDocument tSvgObj = SvgDocument.Open(tData);

                    switch (tExt)
                    {
                        case "jpg":
                            tSvgObj.Draw().Save(tStream, ImageFormat.Jpeg);
                            break;
                        case "png":
                            tSvgObj.Draw().Save(tStream, ImageFormat.Png);
                            break;
                        case "pdf":
                            PdfWriter tWriter = null;
                            Document tDocumentPdf = null;
                            try
                            {
                                //tSvgObj.Draw().Save(tStream, ImageFormat.Png);
                                tDocumentPdf = new Document(new iTextSharp.text.Rectangle((float)tSvgObj.Width, (float)tSvgObj.Height));
                                tDocumentPdf.SetMargins(0.0f, 0.0f, 0.0f, 0.0f);
                                iTextSharp.text.Image tGraph = iTextSharp.text.Image.GetInstance(tStream.ToArray());
                                tGraph.ScaleToFit((float)tSvgObj.Width, (float)tSvgObj.Height);

                                tStream = new MemoryStream();
                                tWriter = PdfWriter.GetInstance(tDocumentPdf, tStream);
                                tDocumentPdf.Open();
                                tDocumentPdf.NewPage();
                                tDocumentPdf.Add(tGraph);
                                tDocumentPdf.Close();
                            }
                            catch (Exception ex)
                            {
                                throw ex;
                            }
                            finally
                            {
                                tDocumentPdf.Close();
                                tWriter.Close();
                                tData.Dispose();
                                tData.Close();

                            }
                            break;
                        case "svg":
                            tStream = tData;
                            break;
                    }
                }
                return File(tStream.ToArray(), tType, tFileName);
            }
            catch (Exception ex)
            {

                return Content(ex.Message);
            }
            
        }