The page load will allways fire before any of the the events caused by
button pushes etc. It is a programatic requirement to be able to do things
at this time before other events load.

Hi, Jason.

re:
!> I found whenever I click the Button control Btn1, then the Page_Load event will be called first.

That's because you're POSTing the page when you click the button.

Please review the ASP.NET Page Lifecycle ...

http://msdn2.microsoft.com/en-us/library/ms178472(VS.80).aspx

re:
!> I am wondering why in the aspx web form, whenever we click any controls, they all call the Page_Load event?

Do you have autopostback set to "true" ?

Juan T. Llibre, asp.net MVP
asp.net faq : http://asp.net.do/faq/
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======================================

The default behavior of a button control is to generate a postback. Other
controls can be set to generate a postback with their events (such as
TextChanged for textbox). A postback is nothing more than a form posting to
itself.

Page_Load always runs when a page is loaded, whether it is a postback or
not. Then, for any other events such as a button click, their event handler
code is run.
-- Peter
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In addition to the other responses, you can use the IsPostBack property of
the Page object to determine whether your code within the Page_xxx events
runs or not...

if (!IsPostBack)
{
   // run when the page first loads
}
else
{
   // run when the page posts back to itself
}