Lists, Loops,

1
Chapter
5

• Lists, Loops,
• Validation, and More

2
Introduction

• This chapter covers the Visual Basic looping
  statements
• Do While
• Do Until
• For Next
• It also discusses the use of
• List Boxes
• Combo Boxes
• As well as presenting some properties and events
  used for user input validation

3
5.1

• Input Boxes

Input Boxes Provide a Simple Way to Gather Input
Without Placing a Text Box on a Form
4
Format of the InputBox Function
InputBox(Prompt ,Title ,Default ,Xpos
,Ypos)

• Prompt - message to the user (required)
• Title - text for the box's title bar
• Default - default text for user's input
• Xpos - X coordinate for the box's position
• Ypos - Y coordinate for the box's position
• Square brackets around Title and following
  arguments indicate these are optional

5
Sample InputBox Usage

• strUserInput InputBox("Enter the distance.", _
  "Provide a Value", "150")
• If the users clicks OK without entering a value,
  150 will be assigned to strUserInput due to the
  default value

6
Xpos, Ypos, and Twips

• Xpos specifies the distance from the left of the
  screen to the left side of the box
• Ypos, from the top of the screen to the top of
  the box
• Both are specified in twips
• One twip is 1/440th inch

7
5.2

• List Boxes

List Boxes Display a List of Items and Allow the
User to Select an Item From the List
8
ListBox Items Property

• This property holds the entire list of items from
  which the user may choose
• The list values may be established at run time or
  as part of the form design
• To set list values in the form design
• Select the list box in the Design window
• Click on ellipses button for the Items property
• This property is a collection, a list of values
• Type each value on a separate line

9
ListBox Items.Count Property

• This property holds the number of items that are
  stored in the Items property
• Example of use
• The number of items in the list can be assigned
  to an integer variable

If lstEmployees.Items.Count 0
Then MessageBox.Show("The list has no
items!") End If
numEmployees lstEmployees.Items.Count
10
Item Indexing

• The Items property values can be accessed from
  your VB code
• Each item value is given a sequential index
• The first item has an index of 0
• The second item has an index of 1, etc.
• Example

name lstCustomers.Items(2) ' Access the 3rd
item value
11
Index Out of Range Error

• The index of the last item is always
  list.Items.Count-1
• Reference to an index greater than Count-1 or
  less than zero throws an exception
• An exception handler can trap this error
• The variable ex captures the exception thrown

Try strInput lstMonths.Items(n).ToString() Catc
h ex as Exception MessageBox.show(ex.Message) End
Try
12
ListBox SelectIndex Property

• Use the SelectIndex property to retrieve the
  index of an item selected by the user
• If no item is selected, the value is set to -1
  (an invalid index value)
• Can use SelectIndex to determine if an item has
  been selected by comparing to -1
• Example

If lstLocations.SelectedIndex ltgt -1
Then location lstLocations.Items(lstLocations.S
electedIndex) End If
13
ListBox SelectedItem Property

• Instead of using the SelectedIndex property as
  follows
• The SelectedItem property can be used to retrieve
  a selected item value as shown

If lstMonths.SelectedIndex ltgt -1 Then month
lstMonths.Items(lstMonths.SelectedIndex) End If
If lstMonths.SelectedIndex ltgt -1 Then month
lstMonths.SelectedItem.Value) End If
14
ListBox Sorted Property

• Sorted is a boolean property
• If true, causes the values in the Items property
  to be displayed in alphabetical order
• If false, values in the Items property are
  displayed in the order they were added

15
ListBox Items.Add Method

• Items can be added to the end of a ListBox list
  in your VB code using the Add method
• Format is
• ListBox.Items.Add(Item)
• ListBox is the name of the control
• Item is the value to add to the Items property
• Example

lstStudents.Items.Add("Sharon")
16
ListBox Items.Insert Method

• Items can be added at a specific position of a
  ListBox in VB code using the Insert method
• ListBox.Items.Insert(Index, Item)
• Index specifies position where Item is placed
• Index is zero based similar to SelectedIndex
  property
• Items that follow are pushed down
• Example inserting "Jean as the 3rd item

lstStudents.Items.Insert(2, "Jean")
17
ListBox Methods to Remove Items

• ListBox.Items.RemoveAt(Index)
• Removes item at the specified index
• ListBox.Items.Remove(Item)
• Removes item with value specified by Item
• ListBox.Items.Clear()
• Removes all items in the Items property
• Examples

lstStudents.Items.RemoveAt(2) remove 3rd
item lstStudents.Items.Remove(Jean) remove
item Jean lstStudents.Items.Clear() remove all
items
18
Other ListBox Methods

• ListBox.Items.Contains(Item)
• Returns true if Item is found in the collection
• ListBox.Items.IndexOf(Item)
• Returns an integer with the index position of the
  first occurrence of Item in the collection
• Examples
• Tutorial 5-1 provides more examples of ListBox
  controls, methods and properties

blnFound lstMonths.Items.Contains(March) intIn
dex lstMonths.Items.IndexOf(March)