 A ListBox control displays a list of items and allows the user to select one or more  Drag from Toolbox to create this control on a form

 The Items property holds an entire list of values from which the user may choose  The list of 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 ◦ View properties & click the Items ellipsis button ◦ This property is a collection, a list of values ◦ Type each value on a separate line

 This property returns an integer with the number of entries stored in the Items property  Example of use:  The number of entries 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

 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

 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() Catch ex as Exception MessageBox.show(ex.Message) End Try

 The SelectIndex property returns an integer with the index of the 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 <> -1 Then location = lstLocations.Items(lstLocations.SelectedIndex) End If

 Instead of using the SelectedIndex property as follows:  The SelectedItem property can be used to retrieve the value of a selected item as follows: If lstMonths.SelectedIndex <> -1 Then month = lstMonths.Items(lstMonths.SelectedIndex) End If If lstMonths.SelectedIndex <> -1 Then month = lstMonths.SelectedItem.ToString) End If

 Sorted is a boolean property  When set to true, values in the Items property are displayed in alphabetical order  When set to false, values in the Items property are displayed in the order they were added

 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 a string value to add to the Items property  Example: lstStudents.Items.Add("Sharon")

 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 3 rd item lstStudents.Items.Insert(2, "Jean")

 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 3 rd item lstStudents.Items.Remove(“Jean”)‘remove item Jean lstStudents.Items.Clear()‘remove all items

 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: blnFound = lstMonths.Items.Contains(“March”) intIndex = lstMonths.Items.IndexOf(“March”)

Slide  The ListBox has a Multicolumn property ◦ Boolean property with default value of false ◦ If set to true, entries can appear side by side  Below, ColumnWidth is set to 30  Note the appearance of a horizontal scroll bar in this case

Slide  A form of ListBox with the list box properties and methods already discussed  One item at a time may be selected but many items in a Checked List Box can be checked  The CheckOnClick property determines how items may be checked ◦ False - user clicks item once to select it, again to check it ◦ True - user clicks item only once to both select it and check it

Slide  The GetItemChecked method returns true if the item at Index has been checked CheckedListBox.GetItemChecked(Index) Dim i as Integer Dim intCheckedCities as Integer = 0 For i = 0 to clbCities.Items.Count – 1 If clbCities.GetItemChecked(i) = True Then intCheckedCities += 1 End If Next i MessageBox.Show(“You checked “ & _ intCheckedCities.Tostring() & “ cities.”)

Slide  Both display a list of items to the user  Both have Items, Items.Count, SelectedIndex, SelectedItem, and Sorted properties  Both have Items.Add, Items.Clear, Items.Remove, and Items.RemoveAt methods  These properties and methods work the same with combo boxes and list boxes

Slide  A combo box also functions like a text box  The user may enter text into a combo box  Or the user may select the text from a series of list box type choices

Slide  If restricting the user to select items listed ◦ If empty space – use ListBox ◦ If limited space – use drop-down list ComboBox  If allowing user to select an item listed or enter an entirely new item ◦ If empty space – use simple ComboBox ◦ If limited space – use drop-down ComboBox

 When you code, you need to anticipate what the user is going to do with your code and what ways they can crash it  Some languages have error messages that you can capture ◦ Once captured you can display to the user an error message

Slide  Numbers are checked to ensure they are within a range of possible values ◦ For example, there are 168 hours in a week ◦ A person can’t work more than 168 hours a week  Values are checked for their “reasonableness” ◦ A person might possibly work 168 hours in a week ◦ However, this is highly improbable  Items selected from a menu or a set of choices are checked to ensure these options are available  Variables are checked for values that might cause problems, such as division by zero

 Empty input ◦ User hits enter before entering data  How would we test for this?  Incorrect Datatype ◦ User enters in a string for a number, etc.  Comparison against a list of acceptable values ◦ State abbreviations ◦ Zip codes

 String length ◦ State abreviation = 2 character strings ◦ How would we test for this?  Numbers in a reasonable range ◦ Hourly wages, salary amounts, # of hours  Dates in reasonable ranges ◦ There is no February 30 th  Time measurements checked