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Chapter 12. Working with List and Combo Boxes > Considering Callback Functions

Considering Callback Functions

A value list control is easy to create, but it has one limitation you should know about. When you set the control’s Row Source Type property to Value List, the Row Source property—the actual list of items—is limited to 2,045 characters or less. Most of the time, this limit will probably be adequate, but when it isn’t, you need another solution such as a callback function to populate the list.

For Access to display a list box, certain parameters about that list box must be known first. For instance, Access must know how many rows and columns of data are in the control. The callback function passes these values to Access. A callback function is similar to any other function, but the difference is that you reference the function in the control’s Row Source Type property. In addition, the callback function uses DAO, so you must reference that library for this populating method to work. That library is already referenced in the sample database, TimeTrack.mdb.


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