要实现功能，上传图片时可以预览，因还有别的文字，所以并不只上传图片，实现与别的文字一起保存，当然上来先上传图片，然后把路径和别的文字一起写入数据库；同时为图片生成缩略图，现只写上传图片方法，文字在ajax里直接传参数就可以了，若要上传多图，修改一下就可以了。

借鉴了网上资料，自己写了一下，并不需要再新加页面，只在一个页面里就OK啦。

JS代码：

//ajax保存数据，后台方法里实现此方法 function SaveData() { filename = document.getElementById("idFile").value; result =test_test_aspx.SaveData(filename).value; if (result) { alert("保存成功！"); } return false; } //实现预览功能 function DrawImage(ImgD) { var preW = 118; var preH = 118; var image = new Image(); image.src = ImgD.src; if (image.width > 0 && image.height > 0) { flag = true; if (image.width / image.height >= preW/ preH) { if (image.width > preW) { ImgD.width = preW; ImgD.height = (image.height * preW) / image.width; } else { ImgD.width = image.width; ImgD.height = image.height; } ImgD.alt = image.width + "x" + image.height; } else { if (image.height > preH) { ImgD.height = preH; ImgD.width = (image.width * preH) / image.height; } else { ImgD.width = image.width; ImgD.height = image.height; } ImgD.alt = image.width + "x" + image.height; } } } //当idFile内容改变时 function FileChange(Value) { flag = false; document.getElementById("showImg").style.display = "none"; document.getElementById("idImg").width = 10; document.getElementById("idImg").height = 10; document.getElementById("idImg").alt = ""; document.getElementById("idImg").src = Value; }

以下为前台代码：

<div> <div><label>图片:</label></div> <div> <input id="idFile" name="pic" type="file" runat="server" onchange="FileChange(this.value);" /> </div> </div> <div> <div><label>预览:</label></div> <div> <img id="idImg" height="0" width="0" src="" alt="" onload="DrawImage(this);" /> //实现预览 <img id="showImg" width="118" height="118" alt="" runat="server"/> //加这个主要是为了实现查看时显示图片，因为上面的（idImg）加上runat="server"报错，如有好的方法可以留言 </div> </div>

以下为AJAX方法：

[Ajax.AjaxMethod()] public bool SaveData(string fileNamePath) { string serverFileName = ""; string sThumbFile = ""; string sSavePath = "~/Files/"; int intThumbWidth = 118; int intThumbHeight = 118; string sThumbExtension = "thumb_"; try { //获取要保存的文件信息 FileInfo file = new FileInfo(fileNamePath); //获得文件扩展名 string fileNameExt = file.Extension; //验证合法的文件 if (CheckFileExt(fileNameExt)) { //生成将要保存的随机文件名 string fileName = GetFileName() + fileNameExt; //检查保存的路径 是否有/结尾 if (sSavePath.EndsWith("/") == false) sSavePath = sSavePath + "/"; //按日期归类保存 string datePath = DateTime.Now.ToString("yyyyMM") + "/" + DateTime.Now.ToString("dd") + "/"; if (true) { sSavePath += datePath; } //获得要保存的文件路径 serverFileName = sSavePath + fileName; //物理完整路径 string toFileFullPath = HttpContext.Current.Server.MapPath(sSavePath); //检查是否有该路径 没有就创建 if (!Directory.Exists(toFileFullPath)) { Directory.CreateDirectory(toFileFullPath); } //将要保存的完整文件名 string toFile = toFileFullPath + fileName; ///创建WebClient实例 WebClient myWebClient = new WebClient(); //设定windows网络安全认证 myWebClient.Credentials = CredentialCache.DefaultCredentials; //要上传的文件 FileStream fs = new FileStream(fileNamePath, FileMode.Open, FileAccess.Read); //FileStream fs = OpenFile(); BinaryReader r = new BinaryReader(fs); //使用UploadFile方法可以用下面的格式 //myWebClient.UploadFile(toFile, "PUT",fileNamePath); byte[] postArray = r.ReadBytes((int)fs.Length); Stream postStream = myWebClient.OpenWrite(toFile, "PUT"); if (postStream.CanWrite) { postStream.Write(postArray, 0, postArray.Length); } postStream.Close(); //以上为原图 try { //原图加载 using (System.Drawing.Image sourceImage = System.Drawing.Image.FromFile(System.Web.HttpContext.Current.Server.MapPath(serverFileName))) { //原图宽度和高度 int width = sourceImage.Width; int height = sourceImage.Height; int smallWidth; int smallHeight; //获取第一张绘制图的大小,(比较 原图的宽/缩略图的宽 和 原图的高/缩略图的高) if (((decimal)width) / height <= ((decimal)intThumbWidth) / intThumbHeight) { smallWidth = intThumbWidth; smallHeight = intThumbWidth * height / width; } else { smallWidth = intThumbHeight * width / height; smallHeight = intThumbHeight; } //判断缩略图在当前文件夹下是否同名称文件存在 int file_append = 0; sThumbFile = sThumbExtension + System.IO.Path.GetFileNameWithoutExtension(fileName) + fileNameExt; while (System.IO.File.Exists(System.Web.HttpContext.Current.Server.MapPath(sSavePath + sThumbFile))) { file_append++; sThumbFile = sThumbExtension + System.IO.Path.GetFileNameWithoutExtension(fileName) + file_append.ToString() + fileNameExt; } //缩略图保存的绝对路径 string smallImagePath = System.Web.HttpContext.Current.Server.MapPath(sSavePath) + sThumbFile; //新建一个图板,以最小等比例压缩大小绘制原图 using (System.Drawing.Image bitmap = new System.Drawing.Bitmap(smallWidth, smallHeight)) { //绘制中间图 using (System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap)) { //高清,平滑 g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High; g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality; g.Clear(Color.Black); g.DrawImage( sourceImage, new System.Drawing.Rectangle(0, 0, smallWidth, smallHeight), new System.Drawing.Rectangle(0, 0, width, height), System.Drawing.GraphicsUnit.Pixel ); } //新建一个图板,以缩略图大小绘制中间图 using (System.Drawing.Image bitmap1 = new System.Drawing.Bitmap(intThumbWidth, intThumbHeight)) { //绘制缩略图 using (System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap1)) { //高清,平滑 g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High; g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality; g.Clear(Color.Black); int lwidth = (smallWidth - intThumbWidth) / 2; int bheight = (smallHeight - intThumbHeight) / 2; g.DrawImage(bitmap, new Rectangle(0, 0, intThumbWidth, intThumbHeight), lwidth, bheight, intThumbWidth,intThumbHeight, GraphicsUnit.Pixel); g.Dispose(); bitmap1.Save(smallImagePath, System.Drawing.Imaging.ImageFormat.Jpeg); return true; } } } } } catch { //出错则删除 System.IO.File.Delete(System.Web.HttpContext.Current.Server.MapPath(serverFileName)); return false; } } else { return false; } } catch (Exception e) { return false; } } /// <summary> /// 检查是否为合法的上传文件 /// </summary> /// <param name="_fileExt"></param> /// <returns></returns> private bool CheckFileExt(string _fileExt) { string[] allowExt = new string[] { ".gif", ".jpg", ".jpeg" }; for (int i = 0; i < allowExt.Length; i++) { if (allowExt[i] == _fileExt) { return true; } } return false; } //生成随机数文件名 public static string GetFileName() { Random rd = new Random(); StringBuilder serial = new StringBuilder(); serial.Append(DateTime.Now.ToString("yyyyMMddHHmmssff")); serial.Append(rd.Next(0, 999999).ToString()); return serial.ToString(); }

以上就是小编为大家带来的AJAX实现图片预览与上传及生成缩略图的方法的全部内容了，希望对大家有所帮助，多多支持查字典教程网~