FileUpload上传图片前首先预览一下
看看效果：
在专案中，创建aspx页面，拉上FileUpload控件一个Image，将用来预览上传时的图片。
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default2.aspx.cs" Inherits="Default2" %>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<div>
<table>
<tr>
<td style="vertical-align: top; width: 10%;">
<fieldset>
<legend>选择图片</legend>
<asp:FileUpload ID="FileUpload1" runat="server" />
</fieldset>
</td>
<td style="vertical-align: top; width: 90%;">
<fieldset>
<legend>预览</legend>
<asp:Image ID="Image1" runat="server" Visible="false" />
</fieldset>
</td>
</tr>
</table>
</div>
</form>
</body>
</html>
在Page_Init事件中，为FileUpload控件，注册onchange客户端事件。
protected void Page_Init(object sender, EventArgs e)
{
this.FileUpload1.Attributes.Add("onchange", Page.ClientScript.GetPostBackEventReference(this.FileUpload1, "onchange"));
}
接下来，Insus.NET创建一个axd处理文档，其实ImageProcessFactory.cs只是一个普通的类别，只实作了IHttpHandler接口。
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ImageProcessFactory.cs using System; using System.Collections.Generic; using System.Drawing; using System.Drawing.Drawing2D; using System.Drawing.Imaging; using System.IO; using System.Linq; using System.Web; using System.Web.SessionState; /// <summary> /// Summary description for ImageProcessFactory /// </summary> namespace Insus.NET { public class ImageProcessFactory : IHttpHandler,IRequiresSessionState { public ImageProcessFactory() { // // TODO: Add constructor logic here // } public void ProcessRequest(HttpContext context) { //Checking whether the UploadBytes session variable have anything else not doing anything if ((context.Session["UploadBytes"]) != null) { byte[] buffer = (byte[])(context.Session["UploadBytes"]); context.Response.BinaryWrite(buffer); } } public bool IsReusable { get { return false; } } } }
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为能应用到axd文档，需要在Web.Config中配置一下。
<configuration>
<system.web>
<httpHandlers>
<add verb="*" path="PreviewImage.axd" type="Insus.NET.ImageProcessFactory"/>
</httpHandlers>
</system.web>
</configuration>
Ok，我们回到aspx.cs页面中，要在page_Load中，怎监控FileUpload控件是否有值变化：
protected void Page_Load(object sender, EventArgs e)
{
if (IsPostBack)
{
var ctrl = Request.Params[Page.postEventSourceID];
var args = Request.Params[Page.postEventArgumentID];
OnchangeHandle(ctrl, args);
}
}
在Page_Load中有一个方法OnchangeHandle(xxx,xxx):
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private void OnchangeHandle(string ctrl, string args) { if (ctrl == this.FileUpload1.UniqueID && args == "onchange") { this.Image1.Visible = true; Session["UploadBytes"] = this.FileUpload1.FileBytes; this.Image1.ImageUrl = "~/PreviewImage.axd" ; } }
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