CLX Reference
TCustomComboBox::OnHighlighted

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Occurs when a new item in the list becomes current.

typedef void __fastcall (__closure *TComboBoxHighlighEvent)(TObject* Sender, int Index);
__property TComboBoxHighlightEvent OnHighlighted = {read=FOnHighlighted write=
FOnHighlighted};

Description

Write an OnHighlighted event handler to respond when the highlighted item in the list changes. For example, you can use OnHighlighted to update a status bar that provides information about the current item.

Sender is the combo box whose current item just changed.

Index is the index of the item that is now highlighted.

Note:    OnHighlighted reflects changes to the current item in the list that are not necessarily selected (that is, the text property has not yet changed.) For example, OnHighlighted occurs several times as the user cursors though the drop-down list. To respond only when an item is selected, use the OnSelect event instead.