PRB: List Boxes and Combo Boxes Lose Item Properties (136588)

SYMPTOMS

When the RowSource property of a ComboBox or ListBox control is set to a value other than 0-None and there are many items in the list, properties of individual items are lost when you scroll down the list. For example, if you select several items from the list, scroll down the list, and then scroll up the list, the selected items might not be highlighted anymore.

CAUSE

This behavior is due to architectural limitations in the manager that handles the lists. When the RowSource is non-zero, the list manager creates 60 items internally and recycles them. This improves performance for lists that have a large number of items. For example, if a list is populated with a million-row table, Visual FoxPro does not have to take the speed and memory penalty associated with creating a million list items. Because they are recycled, properties set on the items are lost during operations such as scrolling. This behavior does not occur in Visual FoxPro 5.0.

RESOLUTION

Populate the controls with the AddItem and RemoveItem methods. These methods create non-recyclable items that are guaranteed to retain their properties.

MORE INFORMATION

Steps to Reproduce Behavior

Place a List box control on a form and add the \VFP\SAMPLES\DATA\Customer table to the Data Environment.

Change the properties of the list box as follows: RowSourceType = 6 RowSource = "customer.contact" MultiSelect = .T.

Run the form and click an item in the list box. Press and hold down the SHIFT key and then press the DOWN ARROW key to select another item in the list box. Now, scroll down the list box to the last item and then scroll back up to the top of the list box. Note that the items are no longer selected.