Text box getting cleared because of update panel

Question

I've have one table, in that table within one I've one and within that , I've update panel whose update mode is set to conditional. Within this update panel I've another table. The table contains 3 text boxes as: old password, new password and confirm password. On the textChanged event of the old password I am checking the user entered value with the value in db. But when the function completes its execution all the 3 text boxes looses its values regardless of whether I update the update panel or not. I don't know why it clears text boxes. I want to prevent text boxes from getting cleared. I tried to get the text box text in string variable and again assign it to text boxes (both in text box text changed event and in page load event under isPostBack condition) but its too, not working.

asp code:

.
.
.
<tr>
    <td colspan="3">
       <div>
           <asp:UpdatePanel ID="updPnlChngPwd" runat="server" UpdateMode="Conditional">
              <ContentTemplate>
                <table style="width:100%">
                  <tr>
                    <td>
                        Old Password
                    </td>
                    <td>:</td>
                    <td>
                        <asp:TextBox ID="txtOldPwd" runat="server" Height="21px" MaxLength="50" TextMode="Password" Width="60%" ontextchanged="txtOldPwd_TextChanged" 
                            AutoPostBack="True"></asp:TextBox>
                    </td>
                  </tr>
                  <tr>
                    <td></td>
                    <td></td>
                    <td>
                        <asp:Label ID="lblWrongOldPwd" runat="server" Text="Wrong Old Password" ForeColor="Red" Visible="False"></asp:Label>
                    </td>
                  </tr>
                  <tr>
                    <td>
                        Password
                    </td>
                    <td>:</td>
                    <td></td>
                  </tr>
                  <tr>
                    <td></td>
                    <td>:</td>
                    <td>
                        <asp:TextBox ID="txtSuppRePwd" runat="server" Height="21px" MaxLength="50" TextMode="Password" Width="60%"></asp:TextBox>
                    </td>
                  </tr>
                  <tr>
                    <td></td>
                    <td>
                      <asp:Button ID="btnUpdPwd" runat="server" Text="Change Password" onclick="btnUpdPwd_Click"/></td>
                    <td>
                    </td>
                  </tr>
                </table>
              </ContentTemplate>
            </asp:UpdatePanel>
         </div>
      <td>
  </tr>
    .
    .
    .

C# code for tetxt box textChanged event:

protected void txtOldPwd_TextChanged(object sender, EventArgs e)
        {
            DataTable dtOldPwd = Obj.DBAccess("select Pwd from Customer where Cust_Id = " + Convert.ToInt32(Session["SuppID"]) + " and Supp_Pwd = '" + txtOldPwd.Text + "'");
            if (dtOldPwd.Rows.Count == 1)
            {
                lblWrongOldPwd.Visible = false;
            }
            else
            {
                lblWrongOldPwd.Visible = true;
                updPnlChngPwd.Update();
            }
        }

Now I am not able to understand what exactly wrong I am doing, does having update panel inside the table causing problem?

Answer 1

     <td>
 <asp:TextBox ID="txtSuppRePwd" runat="server" Height="21px" MaxLength="50" TextMode="Password" Width="60%"></asp:TextBox>
 </td>

You have TextMode set to password which will not save your textbox value . However you will get your textbox value as string on textchange event

 protected void txtbx_TextChanged(object sender, EventArgs e)
        {
            string txtValue = txtbx.Text;
            ViewState["xyz"]= txtValue;   
        }

and you have to save this value in ViewState to use it for btnClick event .

  OR 

You can also set textbox attribute at Page_Load event which is a very bad practice to do like this

protected void Page_Load(object sender, EventArgs e)
 {
      txtbx.Attributes.Add("value", txtbx.Text);