一个关于asp.net的问题

Question

 image.aspx.cs文件内容 

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; 
using System.Drawing.Design; 
using System.Drawing; 
public partial class imagecode : System.Web.UI.Page 
{ 
protected void Page_Load(object sender, EventArgs e) 
{ 
this.CreateCheckCodeImage(RndNum()); 

} 

private string RndNum() 
{ 
int number; 
char code; 
string checkCode = String.Empty; 

System.Random random = new Random(); 

for (int i = 0; i < 4; i++) 
{ 
number = random.Next(); 
if (number % 2 == 0) 
code = (char)('0' + (char)(number % 10)); 
else 
code = (char)('A' + (char)(number % 26)); 
checkCode += code.ToString(); 
} 
Response.Cookies.Add(new HttpCookie("yzmcode", checkCode)); 
return checkCode; 
} 
private void CreateCheckCodeImage(string checkCode) 
{ 
if (checkCode == null || checkCode.Trim() == String.Empty) 
return; 
System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), 22); 
Graphics g = Graphics.FromImage(image); 
try 
{ 
//生成随机生成器 
Random random = new Random(); 
//清空图片背景色 
g.Clear(Color.White); 
//画图片的背景噪音线 
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); 
g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2); 
} 

Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic)); 
System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true); 
g.DrawString(checkCode, font, brush, 2, 2); 
//画图片的前景噪音点 
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())); 
} 
//画图片的边框线 
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); 
Response.ClearContent(); 
Response.ContentType = "image/Gif"; 
Response.BinaryWrite(ms.ToArray()); 
} 
finally 
{ 
g.Dispose(); 
image.Dispose(); 
} 
} 

} 
//验证码使用页login.aspx中的代码 
<asp:ImageButton ID="yzm" runat="server" ImageUrl="imagecode.aspx" /> 
<asp:LinkButton ID="ChangeCode" runat="server" Text="看不清楚？换一个验证码" OnClick="ChangeCode_Click" /> 
<asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="Button" /></div> 
//ogin.aspx.cs中的代码 
添加 
//啥代码也不用写 点击“看不清楚？换一个验证码”以后就可以刷新验证码 
protected void ChangeCode_Click(object sender, EventArgs e) 
{ 
} 
//提交按钮代码这里是通过cookies来验证的 
protected void Button1_Click(object sender, EventArgs e) 
{ 
if (String.Compare(Request.Cookies["yzmcode"].Value, a.Text, true) != 0) 
{ 
Response.Write("<script>alert('验证码错误!')</script>"); 
} 
else 
{ Response.Write("<script>alert('验证吗正确!!!')</script>"); } 
}





我想知道为什么ChangeCode_Click里面不写代码也能刷新验证码

Answer 1

     <script>
        function refreshImg() {
            var img = document.getElementById('<%=yzm.ClientID%>');
            img.src = 'imagecode.aspx?'+new Date().getTime()
        }
    </script>
    <asp:ImageButton ID="yzm" runat="server" ImageUrl="imagecode.aspx" /> 
<asp:LinkButton ID="ChangeCode" runat="server" Text="看不清楚？换一个验证码" OnClick="ChangeCode_Click" OnClientClick="refreshImg()"  />