在 ASP.NET 和 C# 中重复回发表单后的列表

我有一些代码使用 ASP.NET 和 C# 从文件夹中检索文件，我使用 CheckBoxList 显示它们，因为用户将能够选择其中一个文件，然后最后使用按钮，用户将能够通过电子邮件发送该所选项目。

我

遇到的问题是，在选择项目并发送电子邮件后，页面重新加载并且项目重复，我不确定为什么或如何更正。任何帮助将不胜感激。

代码如下：

if (File.Exists(wavFile))
                    {

                        ListItemCollection itemCollection = CheckBoxList2.Items;
                        itemCollection.Add(new ListItem(wavFile));
                        itemCollection.Add(new ListItem("<asp:Panel ID='"Panel1'" runat='"server'"><object id='"MediaPlayer'" width='"100'" height='"42'" classid='"CLSID:22D6F312-B0F6-11D0-94AB-0080C74C7E95'" standby='"Loading Windows Media Player components...'"" +
                                          "type='"application/x-oleobject'"><param name='"FileName'" value='"" + wavFile + "'"><param name='AUTOPLAY' value='0'>" +
                                          "<embed type='"application/x-mplayer2'" src='"" + wavFile + "'" pluginspage='"http://www.microsoft.com/Windows/MediaPlayer/'" name='"MediaPlayer'" uimode='"none'" width='"300'" height='"42'">" +
                                          "</embed></object></asp:Panel><br/><br/>"));

}

然后电子邮件由带有以下代码的按钮控制：

protected void btnSend_Click1(object sender, EventArgs e)
    {
        try
        {
            MailMessage mail = new MailMessage();
            mail.To.Add("email@email.com");
            mail.From = new MailAddress("email@email.com");
            mail.Subject = claimNumber.Text;
            mail.Body = "This is a test of the email again.";
            System.Net.Mail.Attachment attachment;
            attachment = new System.Net.Mail.Attachment(CheckBoxList2.SelectedValue);
            mail.Attachments.Add(attachment);
            mail.IsBodyHtml = true;
            SmtpClient smtp = new SmtpClient();
            smtp.Host = "smtp.email.com"; //Or Your SMTP Server Address
            smtp.Credentials = new System.Net.NetworkCredential
            ("email@email.com", "pa$$w0rd");
            smtp.EnableSsl = true;
            smtp.Send(mail);
            this.labelSuccessIndex.Text = "<br/><strong>The file has been emailed.</strong>";
        }
        catch (Exception ex)
        {
            labelError.Text = ex.Message;
        }
    }

if (!Page.IsPostBack)
{
    if (File.Exists(wavFile))
    {
        // Your code here
    }
}

if (File.Exists(wavFile)) 

if(!Page.IsPostback) { if (File.Exists(wavFile))... }