FileUpload上傳圖片前實現圖片預覽功能(附演示動畫)

2024-07-10 13:23:10

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FileUpload上傳圖片前實現圖片預覽功能(附演示動畫)

在專案中，創建aspx頁面，拉上FileUpload控件一個Image，將用來預覽上傳時的圖片。

復制代碼代碼如下:

View Code
<%@ 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 runat="server">
<div>
<table>
<tr>
<td>
<fieldset>
<legend>選擇圖片</legend>
<asp:FileUpload runat="server" />
</fieldset>
</td>
<td>
<fieldset>
<legend>預覽</legend>
<asp:Image runat="server" Visible="false" />
</fieldset>
</td>
</tr>
</table>
</div>
</form>
</body>
</html>

在Page_Init事件中，為FileUpload控件，注冊onchange客戶端事件。

復制代碼代碼如下:

protected void Page_Init(object sender, EventArgs e)
{
this.FileUpload1.Attributes.Add("onchange", Page.ClientScript.GetPostBackEventReference(this.FileUpload1, "onchange"));
}

接下來，Insus.NET一個axd處理文檔，其實ImageProcessFactory.cs只是一個普能的類別，只實作了IHttpHandler接口。

復制代碼代碼如下:

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;
}
}
}
}

為能能應到axd文檔，需要在Web.Config中配置一下。

復制代碼代碼如下:

View Code
<configuration>
<system.web>
<httpHandlers>
<add verb="*" path="PreviewImage.axd" type="Insus.NET.ImageProcessFactory"/>
</httpHandlers>
</system.web>
</configuration>

Ok，我們回到aspx.cs頁面中，要在page_Load中，怎監控FileUpload控件是否有值變化：

復制代碼代碼如下:

View Code
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中有一個方法OnchangeHandle(xxx,xxx):

復制代碼代碼如下:

View Code
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" ;
}
}