Visual Basic.NET How to Program (PDF)

Chapter 13 Graphical User Interfaces Concepts: Part 2 539
ListBox
properties, methods
and events Description / Delegate and Event Arguments
MultiColumn Indicates whether the ListBox can break a list into multiple columns.
Multiple columns eliminate vertical scrollbars from the display.
SelectedIndex Returns the index of the selected item. If the user selects multiple
items, this property arbitrarily returns one of the selected indices; if no
items have been selected, the property returns -1.
SelectedIndices Returns a collection containing the indices for all selected items.
SelectedItem Returns a reference to the selected item (if multiple items are selected,
it returns the item with the lowest index number).
SelectedItems Returns a collection of the selected item(s).
SelectionMode Determines the number of items that can be selected, and the means
through which multiple items can be selected. Values None, One,
MultiSimple (multiple selection allowed) or MultiExtended
(multiple selection allowed using a combination of arrow keys or
mouse clicks and Shift and Control keys).
Sorted Indicates whether items are sorted alphabetically. Setting this property’s
value to True sorts the items. The default value is False.
Common Method
GetSelected Takes an index as an argument, and returns True if the corresponding
item is selected.
Common Event (Delegate EventHandler, event arguments EventArgs)
SelectedIndex-
Changed
Generated when selected index changes. This is the default event when
the control is double-clicked in the designer.
Fig. 13.10 ListBox properties, methods and events (part 2 of 2).
The SelectionMode property determines the number of items that can be selected.
This property has the possible values None, One, MultiSimple and MultiExtended
(from the SelectionMode enumeration)—the differences among these settings are
explained in Fig. 13.10. The SelectedIndexChanged event occurs when the user
selects a new item.
Both the ListBox and CheckedListBox have properties Items, SelectedItem
and SelectedIndex. Property Items returns all the list items as a collection.
Collections are a common way of exposing lists of Objects in the .NET framework. Many
.NET GUI components (e.g., ListBoxes) use collections to expose lists of internal objects
(e.g., items contained within a ListBox). We discuss collections further in Chapter 23, Data
Structures and Collections. Property SelectedItem returns the ListBox’s currently
selected item. If the user can select multiple items, use collection SelectedItems to return
all the selected items as a collection. Property SelectedIndex returns the index of the
selected item—if there could be more than one, use property SelectedIndices. If no
items are selected, property SelectedIndex returns -1. Method GetSelected takes
an index and returns True if the corresponding item is selected.