上传图片生成等比例缩略图

ImageThumbnail.cs
using System;
using System.IO;
using System.Drawing;
using System.Drawing.Imaging;

public class ImageThumbnail
{
    public Image ResourceImage;
    private int ImageWidth;
    private int ImageHeight;
    public string ErrorMessage;

    public ImageThumbnail(string ImageFileName)
    {
        ResourceImage = Image.FromFile(ImageFileName);
        ErrorMessage = "";
    }

    public bool ThumbnailCallback()
    {
        return false;
    }

    // 方法1，按大小
    public bool ReducedImage(int Width, int Height, string targetFilePath)
    {
        try
        {
            Image ReducedImage;
            Image.GetThumbnailImageAbort callb = new Image.GetThumbnailImageAbort(ThumbnailCallback);
            ReducedImage = ResourceImage.GetThumbnailImage(Width, Height, callb, IntPtr.Zero);
            ReducedImage.Save(@targetFilePath, ImageFormat.Jpeg);
            ReducedImage.Dispose();
            return true;
        }
        catch (Exception e)
        {
            ErrorMessage = e.Message;
            return false;
        }
    }

    // 方法2，按百分比  缩小60% Percent为0.6 targetFilePath为目标路径
    public bool ReducedImage(double Percent, string targetFilePath)
    {
        try
        {
            Image ReducedImage;
            Image.GetThumbnailImageAbort callb = new Image.GetThumbnailImageAbort(ThumbnailCallback);
            ImageWidth = Convert.ToInt32(ResourceImage.Width * Percent);
            ImageHeight = (ResourceImage.Height)*ImageWidth/ ResourceImage.Width;//等比例缩放
            ReducedImage = ResourceImage.GetThumbnailImage(ImageWidth, ImageHeight, callb, IntPtr.Zero);
            ReducedImage.Save(@targetFilePath, ImageFormat.Jpeg);
            ReducedImage.Dispose();
            return true;
        }
        catch (Exception e)
        {
            ErrorMessage = e.Message;
            return false;
        }
    }

}

后台代码：
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
public partial class _Default : System.Web.UI.Page
{

    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void bt_upload_Click(object sender, EventArgs e)
    {
        try
        {
            if (FileUpload1.PostedFile.FileName == "")
            {
                this.lb_info.Text = "请选择文件！";
            }
            else
            {
                string filepath = FileUpload1.PostedFile.FileName;
                string filename = filepath.Substring(filepath.LastIndexOf("\\") + 1);
                string serverpath1 = Server.MapPath("images/") + filename;
                string serverpath2 = Server.MapPath("images/") + System.DateTime.Now.ToString("yyy-MM-dd-hh-mm-ss") + Session.SessionID + filename;
                FileUpload1.PostedFile.SaveAs(serverpath1);
                ImageThumbnail img = new ImageThumbnail(filepath);
                img.ReducedImage(0.4, serverpath2);//0.4表示缩小40%
                this.lb_info.Text = "上传成功！";
            }
        }
        catch (Exception error)
        {
            this.lb_info.Text = "上传发生错误！原因：" + error.ToString();
        }
    }

}

本文来自CSDN博客，转载请标明出处：http://blog.csdn.net/21aspnet/archive/2007/04/01/1548696.aspx

类 ImageThumbnail确实存在问题，生成缩略图都无法删除图片，报资源被占用，通过网上查资料显示要Dispose();，可这个类没有这个方法，于是自己加了一个类

public void DisImage()
    {
        ResourceImage.Dispose();
    }

还有文中在使用类的时候也存在问题

ImageThumbnail img = new ImageThumbnail(filepath);
应该引用的是服务器上的地址，也就是

ImageThumbnail img = new ImageThumbnail(serverpath1);

以下是自己的使用代码

string FileName = FilesSave(FileUpload1, "../AdFile/");

protected static string FilesSave(FileUpload hifile, string RelativePath)
    {
        string filepath = hifile.PostedFile.FileName;
        string GetFileName = "";
        if (filepath != string.Empty)
        {
            //if (IsAllowedExtension(hifile) == true)
            //{
                Random rand = new Random();
                string filename = System.DateTime.Now.ToString("yyyMMddhhmmss") + System.Web.HttpContext.Current.Session.SessionID + filepath.Substring(filepath.LastIndexOf("."));
                string serverpath1 = System.Web.HttpContext.Current.Server.MapPath(RelativePath) + filename;
                string serverpath2 = System.Web.HttpContext.Current.Server.MapPath(RelativePath) + "b_" + filename;
                hifile.PostedFile.SaveAs(serverpath1);    

                ImageThumbnail img = new ImageThumbnail(serverpath1);
                img.ReducedImage(0.4, serverpath2); //0.4表示缩小40%
                img.DisImage();
               
                GetFileName = "b_" + filename;
            //}
        }
        return GetFileName;
    }