TextMode="Password" 添加默认字符

<asp:TextBox ID="User_Password" runat="server" TextMode="Password" CssClass="Myinput" MaxLength="16" onfocus="if(value=='......') {value=''}" onblur="if(value=='') {value='......'}"></asp:TextBox>  添加默认字符
User_Password.Attributes.Add("Value", "......");