When is the Datagrid filled with the data

[nawal]

Hi to you all

I developed a web page (asp.net) using vb (VS 2008)

What I did is I draged a datagrid control into the page and I configured a Data Source from the dialog appeared
I put in the sql query and it went all succesfully
The query is reading a text box value and retrieving the result accordingly

All the code was generated in the default.aspx page

and basically the page is functioning correctly

When I load the page and enter a value in the text box, the datagrid is displaying properly
If there is a data retrived, with the data
If there is not, it would display empty

But what I dont understand is How the datagrid is displayed ?

There is no a button click event handler
and there is no a text box text changed event handler

but when I enter a value in the text box and click enter, the datagrid displays !!

My 2nd question is that how can I test the datagrid when it's filled with the data if it has a data or not?
If there is no data retrieved, I would like to set a lable saying : No data available for the entered value.

Waiting for your reply
Thanks