When is it time to check Page.IsValid property?

Oleg Kolpashchikov · August 13th, 2013, 07:12 PM

I thought that I knew the answer to this question: after Page.Validate() method has run, which normally would be after controls' postback event handlers (MSDN)

Similar examples are in the book:
page 210, page 215, page 220

Code:

protected void Button1_Click(object sender, EventArgs e)
{
   if (Page.IsValid)
   {  Label1.Text = "Valid entry!"; }
}

However, at MCTS test I saw question that offered the following options:
PreInit, Init, PreLoad, Load
All 4 options seem to be wrong.
It is possible to use "Load", if I run Page.Validate()-method myself in Page_Load handler, but otherwise even that is too early.

Am I missing something? I have re-read the chapter 6 on validation and several MSDN pages, but I could find HOW any of these options can be a correct answer.