When the control is bound, its 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.
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 total 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.