处理ASP.NET图片通常会遇见的问题及解决方案介绍

<div>
 <table>
 <tr><td>账号：</td><td>
 <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox></td></tr>
 <tr><td>密码：</td><td>
 <asp:TextBox ID="TextBox2" runat="server" TextMode="Password"></asp:TextBox></td></tr>
 <tr><td>验证码：</td><td>
 <asp:Image ID="Image1" runat="server" ImageUrl="ValidateNo.aspx" /></td></tr>
 <tr><td>请输入：</td><td>
 <asp:TextBox ID="txtyzm" runat="server"></asp:TextBox></td></tr>
 <tr><td>
  <asp:Button ID="btndl" runat="server" Text="登录" onclick="btndl_Click" /></td><td>
  <asp:Button ID="Button2" runat="server" Text="取消" CausesValidation=false /></td></tr>
 </table>
 </div>

protected void Page_Load(object sender, EventArgs e)
 {
  Random r = new Random();
  int i = r.Next(1000, 9999);//生成一个四位的随机数
  Bitmap bit = new Bitmap(100, 40);//生成一个尺寸为100,40的位图
  Graphics g = Graphics.FromImage(bit);//创建一个绘图实例，并以上边创建的的位图为画板，当然这里边也以选择一张已有的图片作为画板。只需要将FromImage（）里的参数换位已存在的Image对象即可
  g.DrawLine(new Pen(Brushes.Blue), new Point(0, 10), new Point(100, 10));
  g.DrawLine(new Pen(Brushes.GreenYellow), new Point(0, 25), new Point(100, 25));//画两条直线，起到一定的模糊验证的码的效果
  g.DrawString(i.ToString(), new Font("宋体", 30), Brushes.Green, new PointF(0, 0));//将生成的四位数的验证码绘到该画板上
  bit.Save(Response.OutputStream, ImageFormat.Jpeg);//将该位图保存为JPEG的格式
  Session["ValidateNo"] = i.ToString();//Seession值保存生成的验证码的值，以便在登录的时候和用户输入的验证码的值做比较
  Response.ContentType = "image/jpeg";//将输入类型改为“Image/jpeg"
  Response.End();
 }

protected void btndl_Click(object sender, EventArgs e)
 {
  if (Session["ValidateNo"] != null)
  {
  string s = Session["ValidateNo"].ToString();
  if (txtyzm.Text != s)
  {
   Response.Write("<script>alert('"+s+"'）</script>");
  }
  else
  {
   Response.Write("<script>alert('OK')</script>");
  }
  }
  else
  {
  Response.Write("<script>alert('验证码暂不存在！')</script>");
  }
 }

 <table style="background:lightblue"><tr><td>选择上传文件：</td><td><asp:FileUpload ID="FileUpload1" runat="server" /></td><td>
  <asp:Button ID="btnupload" runat="server" Text="上传图片"
  onclick="btnupload_Click" /></td></tr>
 <tr><td colspan="3">
  <asp:Image ID="TouXiang" runat="server" /></tr>
 </table> 
然后我们在btnuplod按钮的Click事件的处理函数中做如下操作：
 
protected void btnupload_Click(object sender, EventArgs e)
 {
  if (FileUpload1.FileName.Trim() != "")
  {
  string extension = Path.GetExtension(FileUpload1.FileName);//先获取文件的后缀
  string fileName = DateTime.Now.Year.ToString() + DateTime.Now.Month.ToString() + DateTime.Now.Minute.ToString();//以当前的日期，以年月分的格式为上传的图片重命名
  string path = Server.MapPath(".")+"\\images\\"+fileName + extension;
  FileUpload1.PostedFile.SaveAs(path);//将图片保存在指定路径下
  Bitmap img = new Bitmap(path);//新建一个Bitmap对象并以此为画板
  Graphics g = Graphics.FromImage(img);
  g.DrawString("Hello Olive!", new Font("宋体", 30), Brushes.GreenYellow, new PointF(20,20) );//将"Hello Olive"书写在图片的（20,20）处
  g.Dispose();
  newPath = Server.MapPath(".") + "\\images\\" + fileName + "_New" + extension;
  img.Save(newPath);//将加有文字的图片重新命名并保存，并删除原来的图片
  img.Dispose();
  if (File.Exists(path))
  {
   File.Delete(path);
  }
  touxiangpath="~/images/" + fileName + "_New" + extension;
  }
  else
  {
  Response.Write("<script>alert('请先选择要上传的文件！')</script>");
  }
 }

public static void CutImg(string oPath, string nPaht, int w, int h,string mode)
 {
  Image oimg = Image.FromFile(oPath);
  int nToWidth = w;
  int nToHeight = h;
  int x = 0;
  int y = 0;
  int oWidth = oimg.Width;
  int oHeight = oimg.Height;
  switch (mode)
  {
  case "HW"://按照指定的宽高进行缩放，可能变形
   break;
  case "W"://指定宽度，高按比例缩放
   nToHeight = oWidth * oHeight / nToWidth;
   break;
  case "H"://指定高度，宽按比例缩放
   nToWidth=oWidth*oHeight/nToHeight;
   break;
  case "CUT"://按照指定的宽、高缩放
   if ((oimg.Width / oimg.Height) > (nToWidth / nToHeight))
   {
   oHeight = oimg.Height;
   oWidth = oimg.Height * nToWidth / nToHeight;
   y = 0;
   x = (oimg.Width - oWidth) / 2;
   }
   else
   {
   oWidth = oimg.Width;
   oHeight = oimg.Width * nToHeight / nToWidth;
   x = 0;
   y = (oimg.Height - oHeight) / 2;
   }
   break;
  default: break;
  }
  //新建一个BMP图片
  Image bitmap = new Bitmap(nToWidth, nToHeight);
  //新建一个画板
  Graphics gp = Graphics.FromImage(bitmap);
  gp.InterpolationMode = InterpolationMode.High;
  gp.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
  //清空画布，并以背景色为透明色填充
  gp.Clear(Color.Transparent);
  gp.DrawImage(oimg, new Rectangle(0, 0, nToWidth, nToHeight), new Rectangle(x, y, oWidth, oHeight), GraphicsUnit.Pixel);//绘制出新的略缩图
  try
  {
  bitmap.Save(nPaht, System.Drawing.Imaging.ImageFormat.Jpeg);
  }
  catch(Exception e)
  {
  throw e;
  }
  finally
  {
  oimg.Dispose();
  bitmap.Dispose();
  }
 }

 protected void btnupload_Click(object sender, EventArgs e)
 {
  if (FileUpload1.FileName.Trim() != "")
  {
   //.......
   //.......前边都省略了代码是一样的
   if (File.Exists(path))
  {
   File.Delete(path);
  }
  string p = Server.MapPath(".") + "\\images\\";
  touxiangpath="~/images/" + fileName + "_New" + extension;
  TouXiang.ImageUrl = touxiangpath;
  CutImage.CutImg(newPath, p+"olive.jpg", 100, 200, "CUT");//调用缩放图片的类CutImage的CutImg函数，这里直接保存为了“olive.jpg"是为了方便下面的引用显示，也可保存为其他的名称和格式。
   luesuotu.ImageUrl = "~/images/olive.jpg";
  } 
  else
  {
  Response.Write("<script>alert('请先选择要上传的文件！')</script>");
  }
 }