Visual Basic.NET How to Program (PDF)

Chapter 13 Graphical User Interfaces Concepts: Part 2 545
22
23 ' obtain reference of selected item
24 Dim item As String = chklstInput.SelectedItem
25
26 ' if item checked add to listbox
27 ' otherwise remove from listbox
28 If e.NewValue = CheckState.Checked Then
29 lstDisplay.Items.Add(item)
30 Else
31 lstDisplay.Items.Remove(item)
32 End If
33
34 End Sub ' chklstInput_ItemCheck
35
36 End Class ' FrmCheckedListBox
Fig. 13.14 CheckedListBox and ListBox used in a program to display a user
selection (part 2 of 2).
13.5 ComboBoxes
The ComboBox control combines TextBox features with a drop-down list. A drop-down
list is a GUI component that contains a list from which a value can be selected. It usually
appears as a text box with a down arrow to its right. By default, the user can enter text into
the text box or click the down arrow to display a list of predefined items. If a user chooses
an element from this list, that element is displayed in the text box. If the list contains more
elements than can be displayed in the drop-down list, a scrollbar appears. The maximum
number of items that a drop-down list can display at one time is set by property MaxDrop-
DownItems. Figure 13.15 shows a sample ComboBox in three different states.
As with the ListBox control, the programmer can add objects to collection Items
programmatically, using methods Add and AddRange, or visually, with the String Collection
Editor. Figure 13.16 lists common properties and events of class ComboBox.