如何避免验证触发后返回时被解雇

具有ASPX页面。当用户单击（ ）添加电话号码时，它应该检查并查看是否输入了以前的号码。如果有的话，则只能动态添加另一个文本框以添加另一个电话号码等。但是，它不会在（ ）的印刷机上触发验证触发器，因为它允许该页面执行回发，尽管没有输入任何内容就像该页面进行后背时一样，它会触发我在其他控件上的验证和相应的错误消息。如何避免这种情况？

aspx

    <tr><td class="labels">Tel. No. (XXX-XXXX) </td>
    <td class="tb">
    <asp:TextBox ID="PN1" runat="server" width="120px"></asp:TextBox>
    <asp:ImageButton ID="ImageButtonAdd1" runat="server" ImageUrl="~/Styles/Images/add.jpg" 
     Height="16px" Width="23px"  AlternateText="Add another Phone Number" 
     CausesValidation="False"  Onclick="TelNum2_Click" />
    <asp:RegularExpressionValidator ID="RegularExpressionValidatorPN" runat="server" 
     ErrorMessage="Please enter a VALID Phone Number in the format XXX-XXXX" ControlToValidate="PN1" Display="Dynamic" Font-Italic="True" ForeColor="#FF3300" Font-Bold="True" ValidationExpression="d{3}-d{4}"></asp:RegularExpressionValidator></tr>


  <tr id="phoneNum2" runat="server"><td class="labels"> Tel. No 2. (XXX-XXXX)</td>
  <td class="tb"><asp:TextBox ID="PN2" runat="server" Width="120px"></asp:TextBox>
  <asp:ImageButton ID="ImageButtonAdd2" runat="server" ImageUrl="~/Styles/Images/add.jpg" 
   Height="16px" Width="23px" AlternateText="Add another Phone Number" CausesValidation="False" 
   Onclick="TelNum3" />
  <asp:RegularExpressionValidator ID="RegularExpressionValidatorPN2" runat="server"
   ErrorMessage="Please enter a VALID Phone Number in the format XXX-XXXX" 
   ControlToValidate="PN2" Display="Dynamic" Font-Italic="True" ForeColor="#FF3300" Font-
   Bold="True" ValidationExpression="d{3}-d{4}"></asp:RegularExpressionValidator></td></tr>
   <tr id="phoneNum3" runat="server"><td class="labels"> Tel. No 3. (XXX-XXXX)</td>
   <td class="tb"><asp:TextBox ID="PN3" runat="server" Width="120px"></asp:TextBox>
   <asp:RegularExpressionValidator ID="RegularExpressionValidatorPN3" runat="server" 
    ErrorMessage="Please enter a VALID Phone Number in the format XXX-XXXX" 
    ControlToValidate="PN3" Display="Dynamic" Font-Italic="True" ForeColor="#FF3300" Font-
    Bold="True" ValidationExpression="d{3}-d{4}"></asp:RegularExpressionValidator></td></tr>

cs

     protected void Page_Load(object sender, EventArgs e)
    {
        UpdatePanel1.Visible = true;
        BtnNew.Visible = true;
        BtnDelete.Visible = false;    
        BtnUpdate.Visible = false;
        BtnSave.Visible = false; 
        BtnCancel.Visible = false;
        pubvar.DisableAllControls(Page);
        if (!Page.IsPostBack)
        {
            processAgentData.Visible = false; //area in which textboxes are displayed
            phoneNum2.Visible = false;
            phoneNum3.Visible = false;
        }
        else
        {
            processAgentData.Visible = true;
        }

    }

   protected void TelNum2_Click(object sender, ImageClickEventArgs e)
    {
        try
        {
            if (PN1.Text.Trim().Length > 0)
            {
                phoneNum2.Visible = true;
            }
            else
            {
                phoneNum2.Visible = false;
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine("{0} Exception caught.", ex);
        }
    }
    protected void TelNum3(object sender, EventArgs e)
    {
        try
        {
            if (PN2.Text.Trim().Length > 0)
            {
                phoneNum3.Visible = true;
            }
            else
            {
                phoneNum3.Visible = false;
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine("{0} Exception caught.", ex);
        }
    }