图片上传生成缩略图，并使用JQuery 实现鼠标移动到缩略图显示相应的大图的例子！

代码

<head runat="server">
<script type="text/javascript" src="script/jquery-1.3.2-vsdoc2.js"></script>

    <link href="css/btn.css"  type="text/css" rel="Stylesheet" />
    <title></title>

</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:FileUpload ID="FileUp" runat="server" CssClass="green1" />
        <asp:Button ID="btnUp" runat="server" Text="上传" CssClass="green1"
            onclick="btnUp_Click" /><br />
        <asp:Panel ID="Panel1" runat="server" >
       </asp:Panel>
            <asp:Image ID="ImShow" runat="server" ImageUrl="Images/3f76deb8623b1.jpg" Width="300px"  />
    </div>
       <script  type="text/javascript">


           var $ur = $("#ImShow").attr("src")

           $("image[src*='ico']").hover(function() {
               var $url =$(this).attr("src");
               $("#ImShow").attr("src", $url);
           }, function() {
               $("#ImShow").attr("src", $ur);

           });



    </script>
    </form>
</body>
</html>

代码

  public void QueryIco()
        {

            string path = Server.MapPath("~/Images");
            DirectoryInfo dirinfo = new DirectoryInfo(Server.MapPath("~/ico"));
            FileInfo[] files=dirinfo.GetFiles("*.jpg");
            foreach (FileInfo file in files)
            {

                System.Web.UI.WebControls.Image im = new System.Web.UI.WebControls.Image();
                im.ImageUrl = "ico/"+file.Name;
                this.Panel1.Controls.Add(im);
                if (Panel1.Controls.Count % 4==0)
                {

                    //使Panel中动态换行
                    this.Panel1.Controls.Add(new LiteralControl("<BR>"));
                }


            }

        }

        protected void btnUp_Click(object sender, EventArgs e)
        {
            //得到上传的路径
            string path = Server.MapPath("Images/");
           //得到应用程序虚拟路径
           // string path1 = ApplicationPath + "/Images/";
            string path2=Server.MapPath("~/ico/");
            string type = System.IO.Path.GetExtension(FileUp.FileName).ToLower();
             if(FileUp.HasFile)
             {
                 if (type != ".jpg")
                {
                    Response.Write("<script>alert('文件类型不正确！')</script>");
                }
                else
                {

                        string filename = this.FileUp.FileName;
                        if (FileUp.PostedFile.ContentLength > 1024 *2*1024)
                        {
                            Response.Write("<script>alert('文件不能大于2M！')</script>");
                        }
                        else
                        {
                            FileUp.SaveAs(path+FileUp.FileName);
                            this.ImShow.ImageUrl = "Images/" + FileUp.FileName;
                            MakeSmallImg(FileUp.PostedFile.InputStream, path2 + filename, 100, 200);

                         //   Response.Write("<script>alert('"+path1+"！')</script>");
                            QueryIco();

                        }

                }
             }

        }

        // 按模版比例生成缩略图（以流的方式获取源文件）
        //生成缩略图函数
        //顺序参数：源图文件流、缩略图存放地址、模版宽、模版高
        //注：缩略图大小控制在模版区域内
        public static void MakeSmallImg(System.IO.Stream fromFileStream, string fileSaveUrl, System.Double templateWidth, System.Double templateHeight)
        {
            //从文件取得图片对象，并使用流中嵌入的颜色管理信息
            System.Drawing.Image myImage = System.Drawing.Image.FromStream(fromFileStream, true);


            //缩略图宽、高
            System.Double newWidth = myImage.Width, newHeight = myImage.Height;
            //宽大于模版的横图
            if (myImage.Width > myImage.Height || myImage.Width == myImage.Height)
            {
                if (myImage.Width > templateWidth)
                {
                    //宽按模版，高按比例缩放
                    newWidth = templateWidth;
                    newHeight = myImage.Height * (newWidth / myImage.Width);
                }
            }
            //高大于模版的竖图
            else
            {
                if (myImage.Height > templateHeight)
                {
                    //高按模版，宽按比例缩放
                    newHeight = templateHeight;
                    newWidth = myImage.Width * (newHeight / myImage.Height);
                }
            }

            //取得图片大小
            System.Drawing.Size mySize = new Size((int)newWidth, (int)newHeight);
            //新建一个bmp图片
            System.Drawing.Image bitmap = new System.Drawing.Bitmap(mySize.Width, mySize.Height);
            //新建一个画板

            System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap);
            //设置高质量插值法
            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
            //设置高质量,低速度呈现平滑程度
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
            //清空一下画布
            g.Clear(Color.White);

            //在指定位置画图
            g.DrawImage(myImage, new System.Drawing.Rectangle(0, 0, bitmap.Width, bitmap.Height),
            new System.Drawing.Rectangle(0, 0, myImage.Width, myImage.Height),
            System.Drawing.GraphicsUnit.Pixel);

            ///文字水印
            //System.Drawing.Graphics G=System.Drawing.Graphics.FromImage(bitmap);
            //System.Drawing.Font f=new Font("宋体",10);
            //System.Drawing.Brush b=new SolidBrush(Color.Black);
            //G.DrawString("myohmine",f,b,10,10);
            //G.Dispose();

            ///图片水印
            //System.Drawing.Image copyImage = System.Drawing.Image.FromFile(System.Web.HttpContext.Current.Server.MapPath("pic/1.gif"));
            //Graphics a = Graphics.FromImage(bitmap);
            //a.DrawImage(copyImage, new Rectangle(bitmap.Width-copyImage.Width,bitmap.Height-copyImage.Height,copyImage.Width, copyImage.Height),0,0, copyImage.Width, copyImage.Height, GraphicsUnit.Pixel);

            //copyImage.Dispose();
            //a.Dispose();
            //copyImage.Dispose();

            //保存缩略图
            bitmap.Save(fileSaveUrl, System.Drawing.Imaging.ImageFormat.Jpeg);

            g.Dispose();
            myImage.Dispose();
            bitmap.Dispose();
        }

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原文地址：https://www.cnblogs.com/coderwar/p/1729058.html