Bound and Unbound Controls In Access
You’ve probably heard the terms bound and unbound when creating forms in
Access. Any kind of control that you place on a form—a textbox, an option
button, an image control, and others— can be bound to a record.
When the control is bound, it’s value changes each time you move to a new
record. When you move the record showing Harry Jones’ information, you see
Harry’s address, phone number and maybe his picture. When you move to Sam
Smith’s information, the controls that show address, phone number and picture
change—they are bound to individual records in the database table. There may be
another control that you don’t take notice of, however. Imagine your company
logo in the top left corner of the form. Does it change every time you advance
to a new employee’s information? No—that control is unbound.
Let’s take another example where a bound and an unbound control work
together. Our bookstore has an inventory database so that customers can search
our store by title, author, or subject. In addition to presenting the customer
with text information, we’d like to show a floor plan of our store with a “You
Are Here” box and the location of the book in question. Next to that, we want to
show the cover of the book. See the graphic below. You can download the example
database from our website in uncompressed format (4M)
or if you have WinZip, you can download the compressed
file (833K).
(click to see a larger picture)
In this example, the floor plan is an unbound graphic. Our floor plan does
not change depending on which book the customer is currently viewing—that only
happens at Hogwarts’ library! The graphic of the book cover does change from
record to record—it is a bound graphic.
Not to confuse matters, but there is one ‘hybrid’ graphic in this example.
The red X moves each time the record changes… is it bound or unbound? Even
though it moves, the X does not change! The X graphic is unbound.
We use Visual Basic to reset the position of the X each time the record changes,
but the content of the graphic is always the same. If a book does not have
location information, the X vanishes, but it comes back on the next title that
has location information.
Graphics are an easy example to use for bound and unbound fields, but don’t
think they are the only controls that can be either bound or unbound. If you
want to display all of the books in inventory in a drop-down list so that a
customer can ‘jump’ to the title they’re interested in, that drop-down list is
also unbound. The list of books available does not change depending on which
title the customer is currently viewing! Any control that is stable as you move
through your database is unbound, the ones that constantly update the
information in them are bound.