title: Required Field Validator gets run on post back trigger
body: <p>I have a dropdown list on my aspx page on which I have a RequiredFieldValidator applied over it. DropDown code is: </p>
  
  <pre><code>&lt;asp:DropDownList ID="ddlglCategoryId" runat="server" CssClass="textEntry2" 
                                              AutoPostBack="true" ValidationGroup="Save" DataSourceID="dtsglCategoryId" DataTextField="LookupItem"
                                              DataValueField="Id" AppendDataBoundItems="true"&gt;
                                              &lt;asp:ListItem Text="All" Selected="True" Value="0"&gt;&lt;/asp:ListItem&gt;
                                          &lt;/asp:DropDownList&gt;
  </code></pre>
  
  <p>RequiredFieldValidator code is:</p>
  
  <pre><code>&lt;asp:RequiredFieldValidator ID="rfvddlglCategoryId" InitialValue="0" runat="server"
                                              ErrorMessage="Please select category" CssClass="Validations" ControlToValidate="ddlglCategoryId"
                                              ValidationGroup="Save" Display="Dynamic" SetFocusOnError="true"&gt;
                                          &lt;/asp:RequiredFieldValidator&gt;
  </code></pre>
  
  <p>I have a post back trigger as well on my aspx page and when I change the category from the dropdown, page posts back and a grid on my page gets updated. But due to post back, the validator message appears and then disappears. I want this to appear only when "All" is selected from dropdown and user clicks save button.</p>
  
  <p>Any guidelines?</p>
  
  <p>Trigger:</p>
  
  <pre><code>&lt;/ContentTemplate&gt;
      &lt;Triggers&gt;
          &lt;%--&lt;asp:AsyncPostBackTrigger ControlID="lbFileName" /&gt;--%&gt;
          &lt;asp:PostBackTrigger ControlID="btnFileUploadSave" /&gt;
      &lt;/Triggers&gt;
  &lt;/asp:UpdatePanel&gt;
  </code></pre>
  
  <p>Button:</p>
  
  <pre><code>&lt;asp:ImageButton ID="btnFileUploadSave" runat="server" ValidationGroup="Save"
                                                                          ImageUrl="~/App_Themes/Default/images/update.png" ToolTip="Save"  
                                                                          Height="18px" onclick="btnFileUploadSave_Click"/&gt;
  </code></pre>