You can bind the grid whenever you like.
The method is DataBind()

thanks

Actually, I have a usercontrol, and in all pages of my application, i have that usercontrol

I have a grid in say webform1.aspx, which i want to get populated when that page loads from the login page.

I am trying to do that from the usercontrol, suppliying the input data for it.

Also i am trying to bind it, when some values in the usercontrol is chaged.

eg: test.ascx
page_load(....)
bindgrid(input1, input2)

button1_click(.....)
input1 = new changed value
input2 = new changed value
bindgrid(input1, input2)

sub bindgrid(byval input1 as string, byval input2 as string)
.......
end sub

But on runing the application, from login page to webform, nothing displayed,
when i change some values, and hits the button, an excepton comes object reference not set

This is the real situation now, and without solving this, I cannot go further, unless if someone helps me to figure it out

The first thing I would do is set up a test page using only the datagrid. Get it data bound and working normally.
Once that is set, then I'd add the code for the user control, and see if even putting it on the page caused an error.

If it's still all good, then I'd pop the login page to hit the test page.
Is there an error now?

Baby steps and test pages are great troubleshooting tools.

If you need more help, you need to post real code and the real error, or I can only make guesses at what might be going on.

Your user control may not be saving state as you expect if you're getting an object expected error.