Combo boxes are data entry interface objects used when you want to provide users with the option of selecting an item from a list, OR typing in an entry.

There are times when it is advisable to control the values that a user might enter. Lists are a common data entry object used for this purpose. Lists insure that the user enters a correct value enhancing data integrity and enabling efficient searches and sorts.

The benefits of choosing items from a list are that typos are eliminated, thus any item entered is correctly spelled, and all entries are valid.

For example, if a user wished to enter a value in an Invoice record for "purchase order" in a Payment Method field, they might enter "Purchase Order", or PO", or "P.O." By using a choice list, all users will enter the same value: "Purchase Order". The benefit of this is that if the user wants to do a Query to find all invoices paid by purchase order, the following single criteria search can be done:

Query([Invoices];[Invoice]PaymentMethod ="Purchase Order").

Since the value entered for purchase order will be "Purchase Order", we can be sure that the Query will return all the appropriate records.

Without a choice list, the following multi-criteria search would have to be done:

Query([Invoices];[Invoice]PaymentMethod="Purchase Order";*)

Query([Invoices];|;[Invoice]PaymentMethod ="PO";*)

Query([Invoices];|;[Invoice]PaymentMethod ="P.O.")

4th Dimension provides several ways to implement choice lists:

· 4D's built in choice lists:

· Drop-down lists / Pop-up menus

· Combo boxes



Let's consider each of these options.

4D's built-in choice lists:

4D's built-in choice lists are the easiest to implement because no coding is needed.

However, 4D's built-in choice lists sometimes have a behavior that is NOT what the user needs. That is, the list will pop-up every time the user tabs into the field. Sometimes users wish to be able to tab through the fields without having the choice list pop-up, and they experience this behavior as an interruption in the data entry process.

Field before a 4D built in choice list is displayed:

Field with a 4D built in choice list displayed:

Drop-down lists / Pop-up menus:

These lists are also easy to implement, but not as easy as the built-in choice lists because their implementation requires that some code be written.

When using drop-down lists / pop-up menus, the user is restricted to the items on the menu. There are times where this is exactly the implementation that is needed, and drop-down lists / pop-up menus are a good solution.

However, in some situations a drop-down list / pop-up menu is not desirable because it requires the use of the mouse; the change of data entry mode from keyboard to mouse is experienced as an interruption in the data entry process.

Drop-down list / pop-up menu object before the user clicks on the object with the mouse.

Drop-down list / pop-up menu object after the user clicks on the object with the mouse.

Combo boxes:

Combo boxes are also easy to implement, but again, their implementation requires that some code be written.

Combo boxes solve the user objection to 4D's built-in choice lists popping-up when tabbing through the fields, by enabling the user to tab through the field without the list popping-up. Additionally, combo boxes provide users with the choice of selecting an item from a list, OR typing an entry. When this type of interface is needed, combo boxes are the tool to be used.

Combo box without menu displayed:

Combo box with menu displayed: