以前，在页面上实现缩略图必须借助第三方组件。现在，有了.NET，就可以很轻松地实现缩略图。下面就是实现缩略图的例子。

　　查看例子

　　代码如下：Thumbnail.aspx

＜%@ Page Language="vb" AutoEventWireup="false" Codebehind="Thumbnail.aspx.vb"Inherits="aspxWeb.Thumbnail" %＞＜!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"＞＜HTML＞＜HEAD＞＜title＞在ASP.NET里轻松实现缩略图＜/title＞＜meta content="Microsoft Visual Studio.NET 7.0" name="GENERATOR"＞＜meta content="Visual Basic 7.0" name="CODE_LANGUAGE"＞＜meta content="JavaScript" name="vs_defaultClientScript"＞＜meta content="http://schemas.microsoft.com/intellisense/ie5" name="vs_targetSchema"＞＜/HEAD＞＜body MS_POSITIONING="GridLayout"＞＜asp:Label id="Label1" runat="server"＞＜/asp:Label＞＜form id="Form1" method="post" runat="server" enctype="multipart/form-data"＞＜INPUT type="file" name="file" width="600"＞＜br＞＜br＞＜asp:Button id="Button1" runat="server"＞＜/asp:Button＞＜/form＞＜/body＞＜/HTML＞后代码：Thumbnail.aspx.vbImports SystemImports System.WebImports System.DrawingImports System.IOImports System.Drawing.ImagingPublic Class ThumbnailInherits System.Web.UI.PageProtected WithEvents Label1 As System.Web.UI.WebControls.LabelProtected WithEvents Button1 As System.Web.UI.WebControls.Button#Region " Web Form Designer Generated Code "'This call is required by the Web Form Designer.＜System.Diagnostics.DebuggerStepThrough()＞ Private Sub InitializeComponent()End SubPrivate Sub Page_Init(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Init'CODEGEN: This method call is required by the Web Form Designer'Do not modify it using the code editor.InitializeComponent()End Sub#End RegionPrivate Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.LoadLabel1.Text = "＜h3＞在ASP.NET里轻松实现缩略图＜/h3＞"Button1.Text = "上载并显示缩略图"End SubPrivate Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.ClickDim MyFileColl As HttpFileCollection = HttpContext.Current.Request.FilesDim MyPostedFile As HttpPostedFile = MyFileColl.Item(0)If LCase(MyPostedFile.ContentType.ToString()).IndexOf("image") ＜ 0 ThenResponse.Write("无效的图形格式。")Exit SubEnd IfGetThumbNail(MyPostedFile.FileName, 100, 100, MyPostedFile.ContentType.ToString(),_False, MyPostedFile.InputStream)End SubPrivate Function GetImageType(ByVal strContentType) As System.Drawing.Imaging.ImageFormatSelect Case (strContentType.ToString().ToLower())Case "image/pjpeg"GetImageType = System.Drawing.Imaging.ImageFormat.JpegCase "image/gif"GetImageType = System.Drawing.Imaging.ImageFormat.GifCase "image/bmp"GetImageType = System.Drawing.Imaging.ImageFormat.BmpCase "image/tiff"GetImageType = System.Drawing.Imaging.ImageFormat.TiffCase "image/x-icon"GetImageType = System.Drawing.Imaging.ImageFormat.IconCase "image/x-png"GetImageType = System.Drawing.Imaging.ImageFormat.PngCase "image/x-emf"GetImageType = System.Drawing.Imaging.ImageFormat.EmfCase "image/x-exif"GetImageType = System.Drawing.Imaging.ImageFormat.ExifCase "image/x-wmf"GetImageType = System.Drawing.Imaging.ImageFormat.WmfCase ElseGetImageType = System.Drawing.Imaging.ImageFormat.MemoryBmpEnd SelectEnd FunctionPrivate Sub GetThumbNail(ByVal strFileName, ByVal iWidth, ByVal iheight, ByVal strContentType, _ByVal blnGetFromFile, ByVal ImgStream)Dim oImg As ImageIf blnGetFromFile ThenoImg = oImg.FromFile(strFileName)ElseoImg = oImg.FromStream(ImgStream)End IfoImg = oImg.GetThumbnailImage(iWidth, iheight, Nothing, (New IntPtr()).Zero)Dim strGuid As String = (New Guid()).NewGuid().ToString().ToUpper()Dim strFileExt As String = strFileName.Substring(strFileName.LastIndexOf("."))'保存到本地'oImg.Save(Server.MapPath("images") + "" + strGuid + strFileExt, GetImageType(strContentType))'直接输出url文件'Response.Redirect("images/" + strGuid + strFileExt)'以下显示在屏幕上Response.ContentType = strContentTypeDim MemStream As New MemoryStream()' 注意：这里如果直接用 oImg.Save(Response.OutputStream, GetImageType(strContentType))' 对不同的格式可能会出错，比如Png格式。oImg.Save(MemStream, GetImageType(strContentType))MemStream.WriteTo(Response.OutputStream)End SubEnd Class