why button postback in update panel

Question

I have asp.net button control within update panel. I don't want it to post back but its do post back please suggest me why its post back

<form id="Form1" runat="server">
     <asp:ScriptManager ID="ScriptManager1" runat="server">
     </asp:ScriptManager>
     <asp:FileUpload ID="fuVideo" runat="server" />
     <asp:UpdatePanel ID="UpdatePanel1" runat="server">
         <ContentTemplate>
              <asp:Button ID="btnUploadVideo" UseSubmitBehavior="false" Text="Use selected image" OnClick="btnUploadVideo_Click" CssClass="button close_button hi" runat="server" ClientIDMode="Static" />
         </ContentTemplate>
     <Triggers>
           <asp:PostBackTrigger ControlID="btnUploadVideo" />
     </Triggers>
     </asp:UpdatePanel>
</form>

Answer 1

You can cover your entire controls inside update panel and set trigger..

<form id="Form1" runat="server">
  <asp:ScriptManager ID="ScriptManager1" runat="server">
  </asp:ScriptManager>
  <asp:UpdatePanel ID="UpdatePanel1" runat="server">
  <ContentTemplate>
      <asp:FileUpload ID="fuVideo" runat="server" />

              <asp:Button ID="btnUploadVideo" UseSubmitBehavior="false" Text="Use selected image" OnClick="btnUploadVideo_Click" CssClass="button close_button hi" runat="server" ClientIDMode="Static" />
   </ContentTemplate>
   <Triggers>
           <asp:AsyncPostBackTrigger ControlID="btnUploadVideo" />
   </Triggers>
   </asp:UpdatePanel>
</form>

Note :- Use AsyncPostBackTrigger not PostBackTrigger ...