在ASP.NET里轻松实现缩略图

最新推荐文章于 2015-01-22 21:21:17 发布

转载最新推荐文章于 2015-01-22 21:21:17 发布 · 1k 阅读

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#asp.net #string #object #asp #generator #server

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本文介绍了一种在ASP.NET中创建图片缩略图的方法。通过上传图片，利用.NET内置功能生成指定尺寸的缩略图，并直接输出到浏览器展示。

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。

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>

Thumbnail.aspx.vb

Imports System
Imports System.Web
Imports System.Drawing
Imports System.IO
Imports System.Drawing.Imaging

Public Class Thumbnail 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

Web Form Designer Generated Code

  Private Sub Page_Load()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()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()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()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

using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
using System.IO;
using System.Drawing.Imaging;

namespace eMeng.Exam
... {
/**//// <summary>
/// Thumbnail 的摘要说明。
/// </summary>
public class Thumbnail : System.Web.UI.Page
...{
    protected System.Web.UI.WebControls.Label Label1;
    protected System.Web.UI.WebControls.Button Button1;

    private void Page_Load(object sender, System.EventArgs e)
    ...{
        // 在此处放置用户代码以初始化页面
        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";

    }

    Web 窗体设计器生成的代码

    private void Button1_Click(object sender, System.EventArgs e)
    ...{
        HttpFileCollection MyFileColl = HttpContext.Current.Request.Files;
        HttpPostedFile MyPostedFile = MyFileColl[0];

        if (MyPostedFile.ContentType.ToString().ToLower().IndexOf("image") < 0)
        ...{
            Response.Write("无效的图形格式。");
            return;
        }
        GetThumbNail(MyPostedFile.FileName, 100, 100,
            MyPostedFile.ContentType.ToString(), false, MyPostedFile.InputStream);
    }
    private System.Drawing.Imaging.ImageFormat GetImageType(object strContentType)
    ...{
        if ((strContentType.ToString().ToLower()) == "image/pjpeg")
        ...{
            return System.Drawing.Imaging.ImageFormat.Jpeg;
        }
        else if ((strContentType.ToString().ToLower()) == "image/gif")
        ...{
            return System.Drawing.Imaging.ImageFormat.Gif;
        }
        else if ((strContentType.ToString().ToLower()) == "image/bmp")
        ...{
            return System.Drawing.Imaging.ImageFormat.Bmp;
        }
        else if ((strContentType.ToString().ToLower()) == "image/tiff")
        ...{
            return System.Drawing.Imaging.ImageFormat.Tiff;
        }
        else if ((strContentType.ToString().ToLower()) == "image/x-icon")
        ...{
            return System.Drawing.Imaging.ImageFormat.Icon;
        }
        else if ((strContentType.ToString().ToLower()) == "image/x-png")
        ...{
            return System.Drawing.Imaging.ImageFormat.Png;
        }
        else if ((strContentType.ToString().ToLower()) == "image/x-emf")
        ...{
            return System.Drawing.Imaging.ImageFormat.Emf;
        }
        else if ((strContentType.ToString().ToLower()) == "image/x-exif")
        ...{
            return System.Drawing.Imaging.ImageFormat.Exif;
        }
        else if ((strContentType.ToString().ToLower()) == "image/x-wmf")
        ...{
            return System.Drawing.Imaging.ImageFormat.Wmf;
        }
        else
        ...{
            return System.Drawing.Imaging.ImageFormat.MemoryBmp;
        }
    }

    private void GetThumbNail(string strFileName, int iWidth, int iheight,
        string strContentType, bool blnGetFromFile, System.IO.Stream ImgStream)
    ...{
        System.Drawing.Image oImg;

        if (blnGetFromFile)
        ...{
            oImg = System.Drawing.Image.FromFile(strFileName);
        }
        else
        ...{
            oImg = System.Drawing.Image.FromStream(ImgStream);
        }
        oImg = oImg.GetThumbnailImage(iWidth, iheight, null, IntPtr.Zero);
        string strGuid = System.Guid.NewGuid().ToString().ToUpper();
        string strFileExt = strFileName.Substring(strFileName.LastIndexOf("."));
        Response.ContentType = strContentType;
        MemoryStream MemStream = new MemoryStream();
        oImg.Save(MemStream, GetImageType(strContentType));
        MemStream.WriteTo(Response.OutputStream);
    }

}
}

点击查看演示。该代码在vs.2003中调试成功!