<%@ Page Language="C#" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
 void Alert(string s)
 {
  Page.ClientScript.RegisterStartupScript(Page.GetType(), "js", "alert('" + s + "')", true);
 }
 protected void Button1_Click(object sender, EventArgs e)
 {
  saveFile();
 }
 protected String saveFile()
 {
  String MaxSize = "1024";
  //最大文件大小
  int imgMaxSize = Convert.ToInt32(MaxSize) * 1024 * 1024;
  HttpPostedFile imgFile = FuImg.PostedFile;
  if (imgFile == null || FuImg.FileName == "")
  {
   Alert("請選擇文件。");
   return "";
  }
  String dirPath = Server.MapPath("~/");
  string saveUrl = Page.ResolveUrl("~/");
  if (!System.IO.Directory.Exists(dirPath))
  {
   Alert("上傳目錄不存在。");
   return "";
  }
  String fileName = imgFile.FileName;
  String fileExt = System.IO.Path.GetExtension(fileName).ToLower();
  if (imgFile.InputStream == null || imgFile.InputStream.Length > imgMaxSize)
  {
   Alert("上傳文件大小超過限制。");
   return "";
  }
  //驗證文件格式
  String fpath = IsAllowedExtension(imgFile);
  if ("" == fpath)
  {
   Alert("圖片格式不正確。");
   return "";
  }
  String ymd = DateTime.Now.ToString("yyyyMMdd", System.Globalization.DateTimeFormatInfo.InvariantInfo);
  dirPath += ymd + "/";
  saveUrl = saveUrl + ymd + "/";
  //判斷目錄是否存在
  if (!System.IO.Directory.Exists(dirPath))
  {
   //創(chuàng)建目錄
   System.IO.Directory.CreateDirectory(dirPath);
  }
  String newFileName = Guid.NewGuid().ToString() + fileExt;
  //圖片名字
  String filePath = dirPath + newFileName;
  System.IO.File.Move(fpath, filePath);
  String fileUrl = saveUrl + newFileName;
  Img.ImageUrl = fileUrl;
  //ImageUrl = saveUrl + newFileName;
  return fileUrl;
 }
 public String IsAllowedExtension(HttpPostedFile f)
 {
  String newFile = Server.MapPath("~/" + System.Guid.NewGuid().ToString("D") + ".tmp");
  f.SaveAs(newFile);
  System.IO.FileStream fs = new System.IO.FileStream(newFile, System.IO.FileMode.Open, System.IO.FileAccess.Read);
  System.IO.BinaryReader r = new System.IO.BinaryReader(fs);
  string fileclass = "";
  byte buffer;
  buffer = r.ReadByte();
  fileclass = buffer.ToString();
  buffer = r.ReadByte();
  fileclass += buffer.ToString();
  r.Close();
  fs.Close();
  /* 文件擴展名說明
  *7173    gif 
  *255216   jpg
  *13780    png
  *6677    bmp
   */
  Dictionary<String, String> ftype = new Dictionary<string, string>();
  //添加允許的文件類型
  ftype.Add("7173", "gif");
  ftype.Add("255216", "jpg");
  ftype.Add("13780", "png");
  ftype.Add("6677", "bmp");
  if (ftype.ContainsKey(fileclass))
  {
   return newFile;
  }
  else
  {
   System.IO.File.Delete(newFile);
   return "";
  }
 }
</script>
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
</head>
<body>
 <form id="form1" runat="server">
 <asp:FileUpload ID="FuImg" runat="server" />
 <asp:Button ID="Button1" runat="server" 
 OnClick="Button1_Click" Text="上傳測試" />
 <asp:Image ID="Img" runat="server" />
 </form>
</body>
</html>

希望本文所述對大家的C#程序設計有所幫助。

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