开始日期从   到   
开始日期从</span> <input id ="txt_BeginDate" type ="text" runat ="server"  onfocus="SetDateTime(this);"  /><span>到</span> <input id ="txt_EndDate" type ="text" runat ="server"  onfocus="SetDateTime(this);"  />
改为 7天前到现在 怎么改
 string sdate = (txt_BeginDate.Value == "" ? DateTime.Now.ToShortDateString() : txt_BeginDate.Value);
        string edate = (txt_EndDate.Value == "" ? DateTime.Now.ToShortDateString() : txt_EndDate.Value);