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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.vb
Imports System
Imports System.Web
Imports
System.Drawing
Imports System.IO
Imports
System.Drawing.Imaging
Public Class Thumbnail
Inherits
System.Web.UI.Page
Protected WithEvents Label1 As
System.Web.UI.WebControls.Label
Protected 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 Sub
Private 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 Region
Private Sub
Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs)
Handles MyBase.Load
Label1.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
Sub
Private Sub Button1_Click(ByVal sender As Object, ByVal e As
System.EventArgs) Handles Button1.Click
Dim MyFileColl As
HttpFileCollection = HttpContext.Current.Request.Files
Dim MyPostedFile
As HttpPostedFile = MyFileColl.Item(0)
If
LCase(MyPostedFile.ContentType.ToString()).IndexOf("image") ＜ 0
Then
Response.Write("无效的图形格式。")
Exit Sub
End
If
GetThumbNail(MyPostedFile.FileName, 100, 100,
MyPostedFile.ContentType.ToString(),_
False,
MyPostedFile.InputStream)
End Sub
Private Function
GetImageType(ByVal strContentType) As
System.Drawing.Imaging.ImageFormat
Select Case
(strContentType.ToString().ToLower())
Case
"image/pjpeg"
GetImageType =
System.Drawing.Imaging.ImageFormat.Jpeg
Case
"image/gif"
GetImageType =
System.Drawing.Imaging.ImageFormat.Gif
Case "image/bmp"
GetImageType
= System.Drawing.Imaging.ImageFormat.Bmp
Case
"image/tiff"
GetImageType =
System.Drawing.Imaging.ImageFormat.Tiff
Case
"image/x-icon"
GetImageType =
System.Drawing.Imaging.ImageFormat.Icon
Case
"image/x-png"
GetImageType =
System.Drawing.Imaging.ImageFormat.Png
Case
"image/x-emf"
GetImageType =
System.Drawing.Imaging.ImageFormat.Emf
Case
"image/x-exif"
GetImageType =
System.Drawing.Imaging.ImageFormat.Exif
Case
"image/x-wmf"
GetImageType =
System.Drawing.Imaging.ImageFormat.Wmf
Case Else
GetImageType =
System.Drawing.Imaging.ImageFormat.MemoryBmp
End Select
End
Function
Private Sub GetThumbNail(ByVal strFileName, ByVal iWidth,
ByVal iheight, ByVal strContentType, _
ByVal blnGetFromFile, ByVal
ImgStream)
Dim oImg As Image
If blnGetFromFile Then
oImg =
oImg.FromFile(strFileName)
Else
oImg =
oImg.FromStream(ImgStream)
End If
oImg =
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 =
strContentType
Dim 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
Sub
End Class
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