asp.net ajax實現無重新整理驗證碼

1、首先是在後台驗證碼的aspx檔案的Page_Load中的事件代碼：

using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Web.UI; using System.Web.UI.WebControls; using System.Drawing; namespace 學生線上考試系統 { public partial class AjaxAutoCode : System.Web.UI.Page { //驗證數字 public string authcode = string.Empty; protected void Page_Load(object sender, EventArgs e) { #region 第一種產生驗證碼的方法 Random random = new Random(); authcode = random.Next(1111, 9999).ToString(); //構造圖片 Bitmap image = new Bitmap(authcode.Length * 12, 25); //建立畫布 Graphics g = Graphics.FromImage(image); try { g.Clear(Color.White); for (int i = 0; i < 25; i++) { int x1 = random.Next(image.Width); int x2 = random.Next(image.Width); int y1 = random.Next(image.Height); int y2 = random.Next(image.Height); //連結兩點的線條 g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2); } Font font = new Font("Arial", 12, FontStyle.Bold | FontStyle.Italic); System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush( new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkBlue, 1.2f, true); g.DrawString(authcode, font, brush, 2, 2); //畫圖片的前景噪點 for (int i = 0; i < 100; i++) { int x = random.Next(image.Width); int y = random.Next(image.Height); image.SetPixel(x, y, Color.FromArgb(random.Next())); } g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1); System.IO.MemoryStream ms = new System.IO.MemoryStream(); image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif); ms.WriteTo(this.Response.OutputStream); ms.Close(); this.Response.ContentType = "image/gif"; } finally { image.Dispose(); g.Dispose(); } #endregion } } }

2、其次在顯示驗證碼的頁面定義一個JS函數

function fGetCode() { document.getElementById("getcode").src="Default2.aspx?"+Math.random(); }

3.再編輯前台頁面aspx,下面是前台頁面的程式碼片段

<label>驗證碼</label> <asp:TextBox ID="txt_checkCode" runat="server" Width="178px"></asp:TextBox> <img src="Default2.aspx" alt="看不清楚？" id="getcode"/> <a href="javascript:fGetCode()">更換驗證碼</a>