Forms Data Controls :: Set Text Property Of TextBox In DetailsView To Query String Value?

I'm tyring to write a simple DetailsView only used for inserting new records that will pre-fill a textbox with a query string value. Here's the DetailsView:

[code]....

All I want to do is set VenueID_FK.Text to = the "VenueID" querry string. I also want the user to be able to see the VenueID number as they are filling out GridView1.

I know this is probably a simple thing, but I am very new to asp.net. I thought I could handle this in the page load event, but when I try something like this

TextBox VenueID_FK = (TextBox)DetailsView1.FindControl("VenueID_FK");

And then follow by setting the Text property programitically. I've accomplished something similar to this on a different page using a FormView, but only for ReadOnly mode and it was handled in the databound event on that page.

I get the error "The name 'DetailsView1' doesn't exist in the current context." when trying to do the above mentioned. When trying the same line in the databound event here, I get the same error.