asp.net - DropDownList and Update Panel -

i develop address control, contains 2 dropdownlists (for cities , countries) , several textboxes. second dropdownlist datasource depends on first dropdownlist datasource.

<fieldset>  <legend><%=title%></legend>   <asp:updatepanel id="updatepanel1" runat="server">     <contenttemplate>         <div>             <label for="<%=ddlcountry.clientid %>">country</label>             <asp:dropdownlist runat="server" id="ddlcountry"                datatextfield="name" datavaluefield="id"                datasource="<%#facade.addresses.getcountries() %>"               autopostback="true"                onselectedindexchanged="ddlcountry_selectedindexchanged"             />         </div>         <div>             <label for="<%=ddlcity.clientid %>">city</label>             <asp:dropdownlist runat="server" id="ddlcity"                  datatextfield="name"   datavaluefield="name" />         </div>     </contenttemplate>     <triggers>         <asp:asyncpostbacktrigger controlid="ddlcountry" eventname="selectedindexchanged" />     </triggers> </asp:updatepanel> <div>     <label for="<%=txtstreet.clientid %>">street</label>     <uc:textbox id="txtstreet" text="<%#address.street %>" runat="server" /> </div> <div>     <label for="<%=txtblock.clientid %>">block</label>     <uc:textbox id="txtblock" text="<%#address.block %>" runat="server" /> </div> <div> </fieldset>  

code behind

protected void page_init(object sender, eventargs e)   {      ddlcountry.databind();      if (!ispostback)        {          ddlcity.datasource = facade.addresses.getcities(countryid);          ddlcity.databind();       }  }  protected void ddlcountry_selectedindexchanged(object sender, eventargs e)   {      ddlcity.datasource = facade.addresses.getcities(countryid);      ddlcity.databind();  } 

it works good. if other control on page causes postback, when selectedvalue in ddlcity sets first (default) value.

how avoid it?

move code on page_init page_load , put inside !ispostback

protected void page_load(object sender, eventargs e) {     if (!ispostback)     {         ddlcountry.databind();         ddlcity.datasource = facade.addresses.getcities(countryid);         ddlcity.databind();     } }