ASP.NET的FileUpload控件默認(rèn)是不支持服務(wù)端的onchange事件的，此時(shí)可以用一種變通的方法來(lái)實(shí)現(xiàn)這一功能。
這就需要借用客戶端的onchange事件，調(diào)用__doPostBack方法來(lái)用LinkButton的OnClick事件模擬一個(gè)事件觸發(fā)的過(guò)程，具體代碼如下：

客戶端：

<asp:FileUpload ID="fuPhoto" onchange="javascript:__doPostBack('lbUploadPhoto','')" runat="server" ToolTip="選擇圖片" /><asp:LinkButton ID="lbUploadPhoto" runat="server" OnClick="lbUploadPhoto_Click"></asp:LinkButton>

后臺(tái)代碼：

//自動(dòng)上傳事件protected void lbUploadPhoto_Click(object sender, EventArgs e){fileUpload();}//從控件上傳文件public void fileUpload(){if (fuPhoto.PostedFile != null && fuPhoto.PostedFile.ContentLength > 0){string ext = System.IO.Path.GetExtension(fuPhoto.PostedFile.FileName).ToLower();if (ext != ".jpg" && ext != ".jepg" && ext != ".bmp" && ext != ".gif"){return;}string filename = "Image_" + DateTime.Now.ToString("yyyyMMddHHmmss") + ext;string path = "./UploadPhoto/" + filename;fuPhoto.PostedFile.SaveAs(Server.MapPath(path));Response.Redirect("ImageCut.aspx?Picurl=" + Server.UrlEncode(path));}else{//do some thing;}}